Printing Even and Odd using two Threads in Java

Question

I tried the code below  I took this piece of code from some other post which is correct as per the author  But when I try running  it doesn t give me the exact result    This is mainly to print even and odd values in sequence   public class PrintEvenOddTester          public static void main String     args           Printer print   new Printer false           Thread t1   new Thread new TaskEvenOdd print            Thread t2   new Thread new TaskEvenOdd print            t1 start            t2 start                 class TaskEvenOdd implements Runnable        int number 1      Printer print       TaskEvenOdd Printer print           this print   print              Override     public void run              System out println  Run method            while number lt 10                if number 2    0                   System out println  Number is     number                   print printEven number                   number  2                            else                   System out println  Number is     number                   print printOdd number                   number  2                                           class Printer        boolean isOdd       Printer boolean isOdd           this isOdd   isOdd             synchronized void printEven int number             while isOdd               try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println  Even   number           isOdd   true          notifyAll               synchronized void printOdd int number            while  isOdd               try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println  Odd   number           isOdd   false          notifyAll               Can someone help me in fixing this   EDIT Expected result  Odd 1 Even 2 Odd 3 Even 4 Odd 5 Even 6 Odd 7 Even 8 Odd 9

User · Answer

class PrintNumberTask implements Runnable   Integer count  Object lock   PrintNumberTask int i  Object object        this count   i      this lock   object      Override public void run         while  count  lt   10            synchronized  lock                if  count   2    0                    System out println count                   count                    lock notify                    try                       lock wait                      catch  InterruptedException e                        e printStackTrace                                    else                   System out println count                   count                    lock notify                    try                       lock wait                      catch  InterruptedException e                        e printStackTrace

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public class Solution     static class NumberGenerator        private static volatile boolean printEvenNumber   false         public  void printEvenNumber int i             synchronized  this                 if  printEvenNumber                     try                        wait                       catch  InterruptedException e                         e printStackTrace                                                   System out println i                printEvenNumber    printEvenNumber               notify                            public  void printOddNumber int i                 synchronized  this                    if printEvenNumber                        try                           wait                          catch  InterruptedException e                            e printStackTrace                                                             System out println i                   printEvenNumber    printEvenNumber                  notify                             static  class OddNumberGenerator implements Runnable      private NumberGenerator numberGenerator       public OddNumberGenerator NumberGenerator numberGenerator            this numberGenerator   numberGenerator              Override     public void run             for int i    1  i  lt 100  i   i   2                numberGenerator printOddNumber i                      static class EvenNumberGenerator implements Runnable       private NumberGenerator numberGenerator       public EvenNumberGenerator NumberGenerator numberGenerator            this numberGenerator   numberGenerator              Override     public void run             for  int i   2  i  lt   100  i    i   2               numberGenerator printEvenNumber i                       public static void main String   args        NumberGenerator ng   new NumberGenerator        OddNumberGenerator oddNumberGenerator   new OddNumberGenerator ng       EvenNumberGenerator evenNumberGenerator   new EvenNumberGenerator ng       new Thread oddNumberGenerator  start        new Thread evenNumberGenerator  start

User · Answer

Simple solution     package com code threads   public class PrintOddEven extends Thread        private Object lock      static volatile int count   1       PrintOddEven Object lock            this lock   lock              Override     public void run              while count  lt   10                if  count   2    0                    synchronized lock                       System out println  Even -     count                         count                      try                           lock wait                          catch  InterruptedException e                            e printStackTrace                                                          else                   synchronized lock                       System out println  Odd -     count                         count                      lock notify                                                         public static void main String   args            Object obj   new Object            PrintOddEven even   new PrintOddEven obj           PrintOddEven odd   new PrintOddEven obj            even start            odd start

User · Answer

You can use the following code to get the output with creating two anonymous thread classes   package practice   class Display       boolean isEven   false       synchronized public void printEven int number  throws InterruptedException           while  isEven              wait            System out println  Even       number           isEven   true          notify               synchronized public void printOdd int number  throws InterruptedException           while   isEven              wait            System out println  Odd       number           isEven   false          notify             public class OddEven        public static void main String   args               TODO Auto-generated method stub         final Display disp   new Display              new Thread                 public void run                     int num   0                  for  int i   num  i  lt   10  i    2                        try                           disp printEven i                         catch  InterruptedException e                               TODO Auto-generated catch block                         e printStackTrace                                                                    start             new Thread                 public void run                     int num   1                  for  int i   num  i  lt   10  i    2                        try                           disp printOdd i                         catch  InterruptedException e                               TODO Auto-generated catch block                         e printStackTrace                                                                    start

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Here is the working code to print odd even no alternatively using wait and notify mechanism  I have restrict the limit of numbers to print 1 to 50   public class NotifyTest       Object ob new Object          public static void main String   args           TODO Auto-generated method stub     NotifyTest nt new NotifyTest         even e new even nt ob            odd o new odd nt ob        Thread t1 new Thread e       Thread t2 new Thread o        t1 start             t2 start                 class even implements Runnable       Object lock              int i 2       public even Object ob                this lock ob                     Override     public void run            TODO Auto-generated method stub               while i lt  50                        synchronized  lock                               try                   lock wait                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                               System out println  Even Thread Name-- gt  gt     Thread currentThread   getName      Value-- gt  gt     i               i i 2                                                      class odd implements Runnable        Object lock      int i 1           public odd Object ob                this lock ob              Override     public void run                TODO Auto-generated method stub         while i lt  49                        synchronized  lock                               System out println  Odd Thread Name-- gt  gt     Thread currentThread   getName      Value-- gt  gt     i               i i 2                            lock notify                              try                   Thread sleep 1000                 catch  Exception e                       TODO Auto-generated catch block                 e printStackTrace

User · Answer

1- The number is initialized with 1 and isOdd flag is set to false   set isOdd to true  2-  Increment should be by 1  not by 2  i e  number  1

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This can be acheived using Lock and Condition    import java util concurrent locks Condition  import java util concurrent locks Lock  import java util concurrent locks ReentrantLock   public class EvenOddThreads        public static void main String   args  throws InterruptedException           Printer p   new Printer            Thread oddThread   new Thread new PrintThread p false   Odd               Thread evenThread   new Thread new PrintThread p true   Even              oddThread start            evenThread start              class PrintThread implements Runnable      Printer p      boolean isEven   false       PrintThread Printer p  boolean isEven           this p   p          this isEven   isEven              Override     public void run             int i    isEven  true    2   1          while i  lt  10                if isEven                   p printEven i                else                  p printOdd i                             i i 2                     class Printer       boolean isEven   true      Lock lock   new ReentrantLock        Condition condEven   lock newCondition        Condition condOdd   lock newCondition         public void printEven int no           lock lock            while isEven  true               try                   condEven await                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                                    System out println Thread currentThread   getName    no           isEven   true          condOdd signalAll            lock unlock               public void printOdd int no           lock lock            while isEven  false               try                   condOdd await                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                                    System out println Thread currentThread   getName    no           isEven   false          condEven signalAll            lock unlock

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public class OddEven implements Runnable       public  int count   0        Override     public void run             try               increment              catch  Exception e                   TODO Auto-generated catch block             e printStackTrace                          synchronized void increment   throws Exception           while true                if count lt 10                    count                    System out println Thread currentThread   getName         count                   notify                    wait                 else                   break                                     public static void main String   args            OddEven n1   new OddEven            Thread r1   new Thread n1           Thread r2   new Thread n1            r1 start            r2 start

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public class EvenOddex    public static class print        int n      boolean isOdd   false       synchronized public void printEven int n             while  isOdd                try                   wait                  catch  InterruptedException ex                    Logger getLogger EvenOddex class getName    log Level SEVERE  null  ex                                     System out print Thread currentThread   getName     n     n             isOdd   true          notify               synchronized public void printOdd int n            while   isOdd                try                   wait                  catch  InterruptedException ex                    Logger getLogger EvenOddex class getName    log Level SEVERE  null  ex                                     System out print Thread currentThread   getName     n     n            isOdd   false          notify                public static class even extends Thread        print po       even print po             this po   po           new Thread this   Even   start                 Override     public void run               for  int j   0  j  lt  10  j                  if   j   2     0                    po printEven j                                     public static class odd extends Thread        print po       odd print po             this po   po          new Thread this   Odd   start                Override     public void run              for  int i   0  i  lt  10  i                   if   i   2     0                    po printOdd i                                     public static void main String args          print po   new print        new even po       new odd po

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public class ThreadEvenOdd     static int cnt 0    public static void main String   args         Thread t1   new Thread new Runnable             Override       public void run             synchronized this              while cnt lt 101                if cnt 2  0                  System out print cnt                     cnt                              notifyAll                                               Thread t2   new Thread new Runnable             Override       public void run             synchronized this              while cnt lt 101                if cnt 2  1                  System out print cnt                     cnt                              notifyAll                                               t1 start        t2 start

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This is easiest solution for this problem    public class OddEven implements Runnable        Override     public void run                TODO Auto-generated method stub          for  int i   1  i  lt   10  i                  synchronized  this                    if  i   2    0  amp  amp  Thread currentThread   getName   equals  t2                          try                           notifyAll                            System out println  Even Thread       i                           wait                          catch  InterruptedException e                               TODO Auto-generated catch block                         e printStackTrace                                            else if  i   2    0                          amp  amp  Thread currentThread   getName   equals  t1                          try                           notifyAll                            System out println  Odd Thread       i                           wait                          catch  InterruptedException e                               TODO Auto-generated catch block                         e printStackTrace                                                                                public static void main String   args             OddEven obj   new OddEven            Thread t1   new Thread obj   t1            Thread t2   new Thread obj   t2            t1 start            t2 start

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The other question was closed as a duplicate of this one  I think we can safely get rid of  even or odd  problem and use the wait notify construct as follows   public class WaitNotifyDemoEvenOddThreads                  A transfer object  only use with proper client side locking              static final class LastNumber           int num          final int limit           LastNumber int num  int limit                this num   num              this limit   limit                       static final class NumberPrinter implements Runnable           private final LastNumber last          private final int init           NumberPrinter LastNumber last  int init                this last   last              this init   init                      Override         public void run                 int i   init              synchronized  last                    while  i  lt   last limit                        while  last num    i                            try                               last wait                              catch  InterruptedException e                                e printStackTrace                                                                        System out println Thread currentThread   getName       prints      i                       last num   i   1                      i    2                      last notify                                                         public static void main String   args            LastNumber last   new LastNumber 0  10      or 0  1000         NumberPrinter odd   new NumberPrinter last  1           NumberPrinter even   new NumberPrinter last  0           new Thread odd   o   start            new Thread even   e   start

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This code will also work fine   class Thread1 implements Runnable        private static boolean evenFlag   true       public synchronized void run             if  evenFlag    true                printEven              else              printOdd                         public void printEven             for  int i   0  i  lt   10  i    2                System out println i    Thread currentThread                       evenFlag   false             public  void printOdd             for  int i   1  i  lt   11  i    2                System out println i    Thread currentThread                       evenFlag   true           public class OddEvenDemo        public static void main String   args             Thread1 t1   new Thread1            Thread td1   new Thread t1           Thread td2   new Thread t1           td1 start            td2 start

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import java util concurrent Semaphore    public class PrintOddAndEven    private static class OddThread extends Thread       private Semaphore semaphore      private Semaphore otherSemaphore      private int value   1       public  OddThread Semaphore semaphore  Semaphore otherSemaphore            this semaphore   semaphore          this otherSemaphore   otherSemaphore             public void run             while  value  lt   100                try                      Acquire odd semaphore                 semaphore acquire                    System out println   Odd Thread     value         Thread currentThread   getName                    catch  InterruptedException excetion                    excetion printStackTrace                              value   value   2                 Release odd semaphore             otherSemaphore release                        private static class EvenThread extends Thread       private Semaphore semaphore      private Semaphore otherSemaphore       private int value   2       public  EvenThread Semaphore semaphore  Semaphore otherSemaphore            this semaphore   semaphore          this otherSemaphore   otherSemaphore             public void run             while  value  lt   100                try                      Acquire even semaphore                 semaphore acquire                    System out println   Even Thread     value         Thread currentThread   getName                    catch  InterruptedException excetion                    excetion printStackTrace                              value   value   2                 Release odd semaphore             otherSemaphore release                        public static void main String   args          Initialize oddSemaphore with permit 1     Semaphore oddSemaphore   new Semaphore 1         Initialize evenSempahore with permit 0     Semaphore evenSempahore   new Semaphore 0       OddThread oddThread   new OddThread oddSemaphore  evenSempahore       EvenThread evenThread   new EvenThread evenSempahore  oddSemaphore       oddThread start        evenThread start

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Simple Solution below -  package com test   class MyThread implements Runnable        Override     public void run             int i 1          while true                String name Thread currentThread   getName                if name equals  task1    amp  amp  i 2  0                    System out println name        i                   try                       Thread sleep 1000                     catch  InterruptedException e                        e printStackTrace                                   else if name equals  task2    amp  amp  i 2  0                   System out println name        i                   try                       Thread sleep 1000                     catch  InterruptedException e                        e printStackTrace                                                i                          public static void main String   args             MyThread task1 new MyThread            MyThread task2 new MyThread             Thread t1 new Thread task1  task1            Thread t2 new Thread task2  task2             t1 start            t2 start

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This is my solution to the problem  I have two classes implementing Runnable  one prints odd sequence and the other prints even  I have an instance of Object  that I use for lock  I initialize the two classes with the same object  There is a synchronized block inside the run method of the two classes  where  inside a loop  each method prints one of the numbers  notifies the other thread  waiting for lock on the same object and then itself waits for the same lock again   The classes     public class PrintEven implements Runnable  private Object lock  public PrintEven Object lock        this lock    lock     Override public void run         synchronized  lock            for  int i   2  i  lt   10  i  2                System out println  EVEN    i               lock notify                try                     if i  10  lock wait                    lock wait 500                 catch  InterruptedException e                    e printStackTrace                                           public class PrintOdd implements Runnable   private Object lock  public PrintOdd Object lock        this lock    lock     Override public void run         synchronized  lock            for  int i   1  i  lt   10  i  2                System out println  ODD    i               lock notify                try                     if i  9  lock wait                    lock wait 500                 catch  InterruptedException e                    e printStackTrace                                       public class PrintEvenOdd   public static void main String   args       Object lock   new Object         Thread thread1    new Thread new PrintOdd lock        Thread thread2    new Thread new PrintEven lock        thread1 start        thread2 start          The upper limit in my example is 10  Once the odd thread prints 9 or the even thread prints 10  then we don t need any of the threads to wait any more  So  we can handle that using one if-block  Or  we can use the overloaded wait long timeout  method for the wait to be timed out  One flaw here though  With this code  we cannot guarantee which thread will start execution first   Another example  using Lock and Condition  import java util concurrent locks Condition  import java util concurrent locks Lock  import java util concurrent locks ReentrantLock   public class LockConditionOddEven    public static void main String   args        Lock lock    new ReentrantLock        Condition evenCondition   lock newCondition        Condition oddCondition   lock newCondition        Thread evenThread    new Thread new EvenPrinter 10  lock  evenCondition  oddCondition        Thread oddThread    new Thread new OddPrinter 10  lock  evenCondition  oddCondition        oddThread start        evenThread start       static class OddPrinter implements Runnable      int i   1      int limit      Lock lock      Condition evenCondition      Condition oddCondition       public OddPrinter int limit            super            this limit   limit             public OddPrinter int limit  Lock lock  Condition evenCondition  Condition oddCondition            super            this limit   limit          this lock   lock          this evenCondition   evenCondition          this oddCondition   oddCondition              Override     public void run             while  i  lt  limit                lock lock                System out println  Odd   i               evenCondition signal                i  2              try                   oddCondition await                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                 finally                   lock unlock                                     static class EvenPrinter implements Runnable      int i   2      int limit      Lock lock      Condition evenCondition      Condition oddCondition       public EvenPrinter int limit            super            this limit   limit              public EvenPrinter int limit  Lock lock  Condition evenCondition  Condition oddCondition            super            this limit   limit          this lock   lock          this evenCondition   evenCondition          this oddCondition   oddCondition               Override     public void run             while  i  lt  limit                lock lock                System out println  Even   i               i  2              oddCondition signal                try                   evenCondition await                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                 finally                   lock unlock

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package example   public class PrintSeqTwoThreads        public static void main String   args            final Object mutex   new Object            Thread t1   new Thread                  Override             public void run                     for  int j   0  j  lt  10                         synchronized  mutex                            System out println Thread currentThread   getName           j                           j   j   2                          mutex notify                            try                               mutex wait                              catch  InterruptedException e                                e printStackTrace                                                                                                       Thread t2   new Thread                  Override             public void run                     for  int j   1  j  lt  10                         synchronized  mutex                            System out println Thread currentThread   getName           j                           j   j   2                          mutex notify                            try                               mutex wait                              catch  InterruptedException e                                e printStackTrace                                                                                                       t1 start            t2 start

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I have done it this way  while printing using two threads we cannot predict the sequence which thread    would get executed first so to overcome this situation we have to synchronize the shared resource in    my case the print function which two threads are trying to access   class Printoddeven       public synchronized void print String msg            try               if msg equals  Even                      for int i 0 i lt  10 i  2                        System out println msg     i                       Thread sleep 2000                       notify                        wait                                    else                   for int i 1 i lt  10 i  2                        System out println msg     i                       Thread sleep 2000                       notify                        wait                                              catch  Exception e                e printStackTrace                        class PrintOdd extends Thread      Printoddeven oddeven      public PrintOdd Printoddeven oddeven           this oddeven oddeven             public void run            oddeven print  ODD             class PrintEven extends Thread      Printoddeven oddeven      public PrintEven Printoddeven oddeven           this oddeven oddeven             public void run            oddeven print  Even               public class mainclass        public static void main String   args            Printoddeven obj   new Printoddeven     only one object           PrintEven t1 new PrintEven obj             PrintOdd t2 new PrintOdd obj             t1 start              t2 start

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Simpler Version in Java 8   public class EvenOddPrinter       static boolean flag   true      public static void main String   args            Runnable odd      - gt                for  int i   1  i  lt   10                     if EvenOddPrinter flag                        System out println i                       i  2                      EvenOddPrinter flag    EvenOddPrinter flag                                                      Runnable even      - gt                for  int i   2  i  lt   10                     if  EvenOddPrinter flag                        System out println i                       i  2                      EvenOddPrinter flag    EvenOddPrinter flag                                                       Thread t1   new Thread odd   Odd             Thread t2   new Thread even   Even             t1 start             t2 start

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public class PrintOddEven   private static class PrinterThread extends Thread        private static int current   0      private static final Object LOCK   new Object         private PrinterThread String name  int number            this name   name          this number   number              Override     public void run             while  true                synchronized  LOCK                    try                       LOCK wait 1000                     catch  InterruptedException e                        e printStackTrace                                       if  current  lt  number                        System out println name     current                     else                       break                                     LOCK notifyAll                                       int number      String name     public static void main String   args        new PrinterThread  thread1      20  start        new PrinterThread  thread2      20  start

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Found the solution  Someone looking for solution to this problem can refer  -   public class PrintEvenOddTester        public static void main String    args            Printer print   new Printer            Thread t1   new Thread new TaskEvenOdd print  10  false            Thread t2   new Thread new TaskEvenOdd print  10  true            t1 start            t2 start              class TaskEvenOdd implements Runnable        private int max      private Printer print      private boolean isEvenNumber       TaskEvenOdd Printer print  int max  boolean isEvenNumber            this print   print          this max   max          this isEvenNumber   isEvenNumber              Override     public void run                System out println  Run method            int number   isEvenNumber    true   2   1          while  number  lt   max                 if  isEvenNumber                      System out println  Even     Thread currentThread   getName                     print printEven number                     number  2                else                     System out println  Odd     Thread currentThread   getName                     print printOdd number                      number  2                            number    2                       class Printer        boolean isOdd   false       synchronized void printEven int number             while  isOdd    false                try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println  Even     number           isOdd   false          notifyAll               synchronized void printOdd int number            while  isOdd    true                try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println  Odd     number           isOdd   true          notifyAll               This gives output like   Odd 1 Even 2 Odd 3 Even 4 Odd 5 Even 6 Odd 7 Even 8 Odd 9 Even 10

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Working solution using single class  package com fursa threads      public class PrintNumbers extends Thread         Object lock       PrintNumbers Object lock             this lock   lock             public static void main String ar              Object obj   new Object               This constructor is required for the identification of wait notify            communication         PrintNumbers odd   new PrintNumbers obj           PrintNumbers even   new PrintNumbers obj           odd setName  Odd            even setName  Even            even start            odd start                 Override     public void run             for int i 0 i lt  100 i                   synchronized  lock                     if  Thread currentThread   getName   equals  Even                           if i   2    0                            System out println Thread currentThread   getName       -    i                           try                               lock wait                              catch  InterruptedException e                                e printStackTrace                                                                                           else if  i   2    0                             lock notify                                                             if  Thread currentThread   getName   equals  Odd                           if i   2    1                            System out println Thread currentThread   getName       -    i                           try                               lock wait                              catch  InterruptedException e                                e printStackTrace                                                                                           else if  i   2    1                             lock notify

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package programs multithreading   public class PrintOddEvenNoInSequence    final int upto  final PrintOddEvenNoInSequence obj  volatile boolean oddFlag evenFlag  public PrintOddEvenNoInSequence int upto       this upto   upto      obj   this      oddFlag   true      evenFlag   false    void printInSequence         Thread odd   new Thread new Runnable              Override         public void run                 for int i   1  i  lt   upto  i   i   2                   synchronized  obj                        while  oddFlag                           try                               obj wait                              catch  InterruptedException e                                   TODO Auto-generated catch block                             e printStackTrace                                                                        System out println  Odd   i                       oddFlag   false                      evenFlag   true                      obj notify                                                           Thread even   new Thread new Runnable              Override         public void run                 for int i   2  i  lt   upto  i   i   2                   synchronized  obj                        while  evenFlag                           try                               obj wait                              catch  InterruptedException e                                   TODO Auto-generated catch block                             e printStackTrace                                                                        System out println  Even   i                       oddFlag   true                      evenFlag   false                      obj notify                                                           odd start        even start       public static void main String   args        new PrintOddEvenNoInSequence 100  printInSequence

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I could not understand most of the codes that were here so I wrote myself one  maybe it helps someone like me   NOTE  This does not use separate print even and odd method  One method print   does it all   public class test        private static int START INT   1      private static int STOP INT   10      private static String THREAD 1    Thread A       private static String THREAD 2    Thread B        public static void main String   args            SynchronizedRepository syncRep   new SynchronizedRepository START INT STOP INT           Runnable r1   new EvenOddWorker THREAD 1 syncRep           Runnable r2   new EvenOddWorker THREAD 2 syncRep           Thread t1   new Thread r1  THREAD 1           Thread t2   new Thread r2  THREAD 2           t1 start            t2 start                 public class SynchronizedRepository       private volatile int number      private volatile boolean isSlotEven      private int startNumber      private int stopNumber       public SynchronizedRepository int startNumber  int stopNumber            super            this number   startNumber          this isSlotEven   startNumber 2  0          this startNumber   startNumber          this stopNumber   stopNumber              public synchronized void print String threadName            try               for int i startNumber  i lt  stopNumber 2  i                     if   isSlotEven  amp  amp  number   2    0                              isSlotEven  amp  amp  number   2    0                        System out println threadName        number                       isSlotEven    isSlotEven                      number                                      notifyAll                    wait                              notifyAll              catch  InterruptedException e                e printStackTrace                           public class EvenOddWorker implements Runnable        private String threadName      private SynchronizedRepository syncRep       public EvenOddWorker String threadName  SynchronizedRepository syncRep            super            this threadName   threadName          this syncRep   syncRep              Override     public void run             syncRep print threadName

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Following is my implementation using 2 Semaphores     Odd Semaphore with permit 1  Even Semaphore with permit 0  Pass the two Semaphores to both threads as following signature  my  other  - To Odd thread pass in the order  odd  even  To Even thread pass in this order  even  odd  run   method logic is my acquireUninterruptibly   -  Print -  other release   In Even thread as even Sema is 0 it will block   In Odd thread as odd Sema is available  init to 1  this will print 1 and then release even Sema allowing Even thread to run  Even thread runs prints 2 and release odd Sema allowing Odd thread to run   import java util concurrent Semaphore    public class EvenOdd   private final static String ODD    ODD   private final static String EVEN    EVEN   private final static int MAX ITERATIONS   10   public static class EvenOddThread implements Runnable            private String mType      private int  mNum      private Semaphore mMySema      private Semaphore mOtherSema       public EvenOddThread String str  Semaphore mine  Semaphore other            mType   str          mMySema   mine   new Semaphore 1      start out as unlocked         mOtherSema   other   new Semaphore 0           if str equals ODD                 mNum   1                    else               mNum   2                        Override     public void run                           for  int i   0  i  lt  MAX ITERATIONS  i                      mMySema acquireUninterruptibly                    if  mType equals ODD                         System out println  Odd Thread -     mNum                     else                       System out println  Even Thread -     mNum                                     mNum    2                  mOtherSema release                                           public static void main String   args  throws InterruptedException           Semaphore odd   new Semaphore 1           Semaphore even   new Semaphore 0            System out println  Start               System out println             Thread tOdd   new Thread new EvenOddThread ODD                                    odd                                    even            Thread tEven   new Thread new EvenOddThread EVEN                                    even                                    odd             tOdd start            tEven start             tOdd join            tEven join             System out println            System out println  Done                          Following is the output -  Start     Odd Thread - 1 Even Thread - 2 Odd Thread - 3 Even Thread - 4 Odd Thread - 5 Even Thread - 6 Odd Thread - 7 Even Thread - 8 Odd Thread - 9 Even Thread - 10 Odd Thread - 11 Even Thread - 12 Odd Thread - 13 Even Thread - 14 Odd Thread - 15 Even Thread - 16 Odd Thread - 17 Even Thread - 18 Odd Thread - 19 Even Thread - 20  Done

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public class OddAndEvenThreadProblems               private static Integer i   0               public static void main String   args                    new EvenClass   start                    new OddClass   start                                public static class EvenClass extends Thread                    public void run                         while  i  lt  10                            synchronized  i                                if  i   2    0                                     try                                       Thread sleep 1000                                       System out println   EvenClass     i                                       i   i   1                                    catch  Exception e                                        e printStackTrace                                                                                                                                                                  public static class OddClass extends Thread                     Override                 public void run                         while  i  lt  10                            synchronized  i                                if  i   2    1                                    try                                       Thread sleep 1000                                       System out println   OddClass      i                                       i   i   1                                    catch  Exception e                                        e printStackTrace                                                                                                                                                OUTPUT will be  -    EvenClass 0  OddClass  1  EvenClass 2  OddClass  3  EvenClass 4  OddClass  5  EvenClass 6  OddClass  7  EvenClass 8  OddClass  9

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package com example   public class MyClass        static int mycount 0      static Thread t      static Thread t2      public static void main String   arg                t2 new Thread new Runnable                  Override             public void run                     System out print mycount       even  n                    try                       Thread sleep 500                     catch  InterruptedException e                        e printStackTrace                                      if mycount gt 25                      System exit 0                   run                                      t new Thread new Runnable                  Override             public void run                     System out print mycount       odd  n                    try                       Thread sleep 500                     catch  InterruptedException e                        e printStackTrace                                      if mycount gt 26                      System exit 0                   run                                      t start            t2 start

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I think the solutions being provided have unnecessarily added stuff and does not use semaphores to its full potential  Here s what my solution is   package com test threads   import java util concurrent Semaphore   public class EvenOddThreadTest        public static int MAX   100      public static Integer number   new Integer 0          Unlocked state     public Semaphore semaphore   new Semaphore 1       class PrinterThread extends Thread            int start   0          String name           PrinterThread String name  int start                this start   start              this name   name                      Override         public void run                 try                  while start  lt  MAX                          try to acquire the number of semaphore equal to your value                        and if you do not get it then wait for it                  semaphore acquire start                   System out println name           start                      prepare for the next iteration                  start  2                     release one less than what you need to print in the next iteration                     This will release the other thread which is waiting to print the next number                  semaphore release start-1                                   catch InterruptedException e                                       public static void main String args              EvenOddThreadTest test   new EvenOddThreadTest            PrinterThread a   test new PrinterThread  Even  1           PrinterThread b   test new PrinterThread  Odd   2           try               a start                b start              catch  Exception e

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import java util concurrent atomic AtomicInteger    public class PrintEvenOddTester         public static void main String     args               Printer print   new Printer false               Thread t1   new Thread new TaskEvenOdd print   Thread1   new AtomicInteger 1                 Thread t2   new Thread new TaskEvenOdd print  Thread2    new AtomicInteger 2                 t1 start                t2 start                 class TaskEvenOdd implements Runnable       Printer print      String name      AtomicInteger number      TaskEvenOdd Printer print  String name  AtomicInteger number           this print   print          this name   name          this number   number              Override     public void run              System out println  Run method            while number get   lt 10                if number get   2    0                   print printEven number get   name                             else                   print printOdd number get   name                             number addAndGet 2                                class Printer       boolean isEven       public Printer             public Printer boolean isEven            this isEven   isEven             synchronized void printEven int number  String name             while   isEven                try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println name    Even     number           isEven   false          notifyAll               synchronized void printOdd int number  String name            while  isEven                try                   wait                  catch  InterruptedException e                    e printStackTrace                                    System out println name    Odd     number           isEven   true          notifyAll

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Please use the following code to print odd and even number in a proper order along with desired messages   package practice    class Test      private static boolean oddFlag   true    int count   1     private void oddPrinter         synchronized  this          while true            try             if count  lt  10                if oddFlag                  Thread sleep 500                 System out println Thread currentThread   getName            count                   oddFlag    oddFlag                notifyAll                              else                 wait                                        else               System out println  Odd Thread finished                notify                break                                catch  InterruptedException e              e printStackTrace                                   private void evenPrinter         synchronized  this          while  true            try             if count  lt  10                if  oddFlag                  Thread sleep 500                 System out println Thread currentThread   getName            count                   oddFlag    oddFlag                notify                              else                 wait                                        else               System out println  Even Thread finished                notify                break                                catch  InterruptedException e              e printStackTrace                                    public static void main String   args  throws InterruptedException      final Test test   new Test         Thread t1   new Thread new Runnable           public void run             test oddPrinter                    Thread 1         Thread t2   new Thread new Runnable           public void run             test evenPrinter                    Thread 2         t1 start        t2 start         t1 join        t2 join         System out println  Main thread finished

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private Object lock   new Object       private volatile boolean isOdd   false        public void generateEvenNumbers int number  throws InterruptedException            synchronized  lock                while  isOdd    false                                 lock wait                              System out println number               isOdd   false              lock notifyAll                         public void generateOddNumbers int number  throws InterruptedException            synchronized  lock                while  isOdd    true                    lock wait                              System out println number               isOdd   true              lock notifyAll

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Simplest Solution     public class OddEvenWithThread       public static void main String a              Thread t1   new Thread new OddEvenRunnable 0    Even Thread            Thread t2   new Thread new OddEvenRunnable 1    Odd Thread             t1 start            t2 start             class OddEvenRunnable implements Runnable       Integer evenflag      static Integer number   1      static Object lock   new Object         OddEvenRunnable Integer evenFlag            this evenflag   evenFlag              Override     public void run             while  number  lt  10                synchronized  lock                    try                       while  number   2    evenflag                            lock wait                                            catch  InterruptedException e                        e printStackTrace                                       System out println Thread currentThread   getName           number                   number                    lock notifyAll

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Class to print odd Even number  public class PrintOddEven implements Runnable        private int max      private int number       public  PrintOddEven int max number int number            max   max number          this number   number              Override     public void run               while number lt  max                        if Thread currentThread   getName   equalsIgnoreCase  odd                                  try                       printOdd                      catch  InterruptedException e                           TODO Auto-generated catch block                     e printStackTrace                                                else                               try                       printEven                      catch  InterruptedException e                           TODO Auto-generated catch block                     e printStackTrace                                                            public synchronized void printOdd   throws InterruptedException                if number 2  0                        wait                       System out println number Thread currentThread   getName             number            notifyAll               public synchronized void printEven   throws InterruptedException                if number 2  0                        wait                       System out println number Thread currentThread   getName             number            notifyAll               Driver Program  public class OddEvenThread        public static void main String   args             PrintOddEven printer   new PrintOddEven 10 1             Thread thread1   new Thread printer  odd            Thread thread2   new Thread  printer  even             thread1 start            thread2 start

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public class Main       public static void main String   args  throws Exception          int N   100          PrintingThread oddNumberThread   new PrintingThread N - 1           PrintingThread evenNumberThread   new PrintingThread N           oddNumberThread start               make sure that even thread only start after odd thread         while   evenNumberThread isAlive                  if oddNumberThread isAlive                      evenNumberThread start                  else                   Thread sleep 100                                     class PrintingThread extends Thread       private static final Object object   new Object       lock for both threads     final int N         N determines whether given thread is even or odd     PrintingThread int N            this N   N              Override     public void run             synchronized  object                int start   N   2    0   2   1     if N is odd start from 1 else start from 0             for  int i   start  i  lt   N  i   i   2                    System out println i                   try                       object notify       will notify waiting thread                     object wait       will make current thread wait                   catch  InterruptedException e                        e printStackTrace

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package pkgscjp   public class OddPrint implements Runnable        public static boolean flag   true       public void run             for  int i   1  i  lt   99                 if  flag                    System out println i                   flag   false                  i   i   2                                     package pkgscjp   public class EvenPrint implements Runnable       public void run             for  int i   2  i  lt   100                 if   OddPrint flag                    System out println i                   OddPrint flag   true                  i   i   2                                     package pkgscjp   public class NaturalNumberThreadMain       public static void main String args              EvenPrint ep   new EvenPrint            OddPrint op   new OddPrint            Thread te   new Thread ep           Thread to   new Thread op           to start            te start

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See the Clean implementation  public class PrintOddEvenByTwoThreads       static int number   1      static Thread odd      static Thread even      static int max   10       static class OddThread extends Thread            Override         public void run                 while  number  lt   max                    if  number   2    1                        System out println Thread currentThread          number                       else                        synchronized  odd                            synchronized  even                                even notify                                                      try                               wait                              catch  InterruptedException e                                e printStackTrace                                                                                                         static class EvenThread extends Thread            Override         public void run                 while  number  lt   max                    if  number   2    0                        System out println Thread currentThread          number                       else                        synchronized  even                            synchronized  odd                                odd notify                                                      try                               wait                              catch  InterruptedException e                                e printStackTrace                                                                                                         public static void main String   args  throws InterruptedException           odd   new OddThread            even   new EvenThread            odd start            even start

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public class Multi extends Thread        public static int a      static a 1       public void run              for int i 1 i lt 5 i               System out println  Thread Id    this getId      Value   a             try Thread sleep 500   catch InterruptedException e  System out println e                           public static void main String args              Multi t1 new Multi             Multi t2 new Multi             t1 start            t2 start

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Here is the code which I made it work through a single class  package com learn thread   public class PrintNumbers extends Thread   volatile static int i   1  Object lock   PrintNumbers Object lock        this lock   lock     public static void main String ar          Object obj   new Object           This constructor is required for the identification of wait notify        communication     PrintNumbers odd   new PrintNumbers obj       PrintNumbers even   new PrintNumbers obj       odd setName  Odd        even setName  Even        odd start        even start        Override public void run         while  i  lt   10            if  i   2    0  amp  amp  Thread currentThread   getName   equals  Even                  synchronized  lock                    System out println Thread currentThread   getName       -                             i                   i                    try                       lock wait                      catch  InterruptedException e                        e printStackTrace                                                      if  i   2    1  amp  amp  Thread currentThread   getName   equals  Odd                  synchronized  lock                    System out println Thread currentThread   getName       -                             i                   i                    lock notify                                                     Output   Odd - 1 Even - 2 Odd - 3 Even - 4 Odd - 5 Even - 6 Odd - 7 Even - 8 Odd - 9 Even - 10 Odd - 11

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Use this following very simple JAVA 8 Runnable Class feature  public class MultiThreadExample    static AtomicInteger atomicNumber   new AtomicInteger 1    public static void main String   args        Runnable print      - gt            while  atomicNumber get    lt  10                synchronized  atomicNumber                    if   atomicNumber get     2    0   amp  amp   Even  equals Thread currentThread   getName                           System out println  Even          atomicNumber getAndIncrement                       else if   atomicNumber get     2    0   amp  amp   Odd  equals Thread currentThread   getName                           System out println  Odd          atomicNumber getAndIncrement                                                           Thread t1   new Thread print       t1 setName  Even        t1 start        Thread t2   new Thread print       t2 setName  Odd        t2 start

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The same can be done with Lock interface   import java util concurrent locks Condition  import java util concurrent locks Lock  import java util concurrent locks ReentrantLock   public class NumberPrinter implements Runnable       private Lock lock      private Condition condition      private String type      private static boolean oddTurn   true       public NumberPrinter String type  Lock lock  Condition condition            this type   type          this lock   lock          this condition   condition             public void run             int i   type equals  odd     1   2          while  i  lt   10                if  type equals  odd                    printOdd i               if  type equals  even                    printEven i               i   i   2                       private void printOdd int i               synchronized  lock            lock lock            while   oddTurn                try                      lock wait                    condition await                  catch  InterruptedException e                    e printStackTrace                                    System out println type         i           oddTurn   false             lock notifyAll            condition signalAll            lock unlock                         private void printEven int i               synchronized  lock            lock lock            while  oddTurn                try                      lock wait                    condition await                  catch  InterruptedException e                    e printStackTrace                                    System out println type         i           oddTurn   true             lock notifyAll            condition signalAll            lock unlock                         public static void main String   args            Lock lock   new ReentrantLock            Condition condition   lock newCondition            Thread odd   new Thread new NumberPrinter  odd   lock  condition            Thread even   new Thread new NumberPrinter  even   lock  condition            odd start            even start

[java] Printing Even and Odd using two Threads in Java

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