Stack array using pop and push

Question

I have a problem with 2 classes that I have created for a program the uses the stack  The first problem that I get is that when I try to run the program I get a run time error   Its kind of a difficult thing to ask because it doing several things  It asks for user input to add numbers to the stack and checking if the stack is full or empty  I also may need help to copy the array      Exception in thread  main  java lang ArrayIndexOutOfBoundsException    -1       at IntegerStack push IntegerStack java 24        at Lab15 main Lab15 java 38    This is the main class that runs the program   import java util Scanner    public class Lab15        public static void main String   args                System out println        Playing with an Integer Stack                  final int SIZE   5          IntegerStack myStack   new IntegerStack SIZE           Scanner scan   new Scanner System in              Pushing integers onto the stack         System out println  Please enter an integer to push onto the stack - OR -  q  to Quit            while scan hasNextInt                          int i   scan nextInt                myStack push i               System out println  Pushed    i                        Pop a couple of entries from the stack         System out println  Lets pop 2 elements from the stack            int count   0          while  myStack isEmpty    amp  amp  count lt 2                        System out println  Popped   myStack pop                 count                       scan next      Clearing the Scanner to get it ready for  further input             Push a few more integers onto the stack         System out println  Push in a few more elements - OR - enter q to quit            while scan hasNextInt                          int i   scan nextInt                myStack push i               System out println  Pushed    i                      System out println   nThe final contentes of the stack are             while  myStack isEmpty                          System out println  Popped   myStack pop                           This is the class that is adding the numbers to the stack which is what has the problems  This is where I may need help copying the array  At the end    import java util Arrays   public class IntegerStack        private int stack         private int top        public IntegerStack int SIZE                 stack   new int  SIZE           top   -1             public void push int i                 if  top    stack length                        extendStack                       stack top   i          top               public int pop                  top --          return stack top              public int peek                 return stack top              public boolean isEmpty                  if   top    -1                         return true                       private void extendStack                 int    copy   Arrays copyOf stack  stack length             Any help or direction will be appreciated

User · Answer

Stack Implementation in Java

  class stack
  {  private int top;
     private int[] element;
      stack()
      {element=new int[10];
      top=-1;
      }
      void push(int item)
      {top++;
      if(top==9)
          System.out.println("Overflow");
      else
              {
               top++;
      element[top]=item;

      }

      void pop()
      {if(top==-1)
          System.out.println("Underflow");
      else  
      top--;
      }
      void display()
      {
          System.out.println("\nTop="+top+"\nElement="+element[top]);
      }

      public static void main(String args[])
      {
        stack s1=new stack();
        s1.push(10);
        s1.display();
        s1.push(20);
        s1.display();
        s1.push(30);
        s1.display();
        s1.pop();
        s1.display();
      }

  }

Output



Top=0
Element=10

Top=1
Element=20

Top=2
Element=30

Top=1
Element=20

User · Answer

Because you initialized the top variable to -1 in your constructor  you need to increment the top variable in your push   method before you access the array  Note that I ve changed the assignment to use   top   public void push int i         if  top    stack length                extendStack               stack   top   i      That will fix the ArrayIndexOutOfBoundsException you posted about  I can see other issues in your code  but since this is a homework assignment I ll leave those as  an exercise for the reader

User · Answer

Better solution for your Stack implementation   import java util List  import java util ArrayList  public class IntegerStack          private List lt Integer gt  stack       public IntegerStack int SIZE                 stack   new ArrayList lt Integer gt  SIZE              public void push int i                 stack add 0 i                public int pop                    if  stack isEmpty                int i  stack get 0              stack remove 0              return i            else             return -1    Or any invalid value                        public int peek                  if  stack isEmpty                return stack get 0             else             return -1    Or any invalid value                         public boolean isEmpty                  stack isEmpty                 If you have to use Array    Here are problems in your code and possible solutions  import java util Arrays  public class IntegerStack         private int stack         private int top        public IntegerStack int SIZE            stack   new int  SIZE       top   -1     top should be 0  If you keep it as -1  problems will arise when SIZE is passed as 0          In your push method -1  0 will be false and your code will try to add the invalid element to Stack             Solution top 0            public void push int i         if  top    stack length                extendStack                  stack top   i          top        public int pop          top --     here you are reducing the top before giving the Object back       Solution        if  isEmpty           int value   stack top          top --       return value         else        return -1    OR invalid value                 return stack top      public int peek         return stack top      Problem when stack is empty or size is 0       Solution         if  isEmpty              return stack top           else           return -1    Or any invalid value                       public boolean isEmpty          if   top    -1      problem    we changed top to 0 above so here it need to check if its 0 and there should be no semicolon after the if statement       Solution if top  0                   return true           private void extendStack          int    copy   Arrays copyOf stack  stack length      The second parameter in Arrays copyOf has no changes  so there will be no change in array length      Solution       stack Arrays copyOf stack  stack length 1

User · Answer

public class Stack        int   arr       int MAX SIZE       int top   public Stack int n       MAX SIZE   n      arr   new int MAX SIZE       top 0         public boolean isEmpty            if top   0              return true        else         return false        public boolean push int ele        if top lt MAX SIZE           arr top    ele          top            return true            else          System out println  Stack is full            return false          public void show        for int element arr           System out print element               public int size        return top       public int peek            if  isEmpty                 int peekTest   arr top-1               return peekTest                           else         System out println  Stack is empty           return 0          public int pop        if isEmpty             System out println  Stack is Emmpty            return 0            else          int element   arr --top           return element

User · Answer

Here is an example of implementing stack in java  Array Based implementation    public class MyStack extends Throwable               private static final long serialVersionUID   -4433344892390700337L   protected static int top   -1  protected static int capacity  protected static int size   public int stackDatas     null   public MyStack        stackDatas   new int 10       capacity   stackDatas length     public static int size         if top  lt  0           size   top   1          return size            size   top 1      return size      public void push int data       if capacity    size             System out println  no memory         else          stackDatas   top    data           public boolean topData        if top  lt  0           return true       else          System out println stackDatas top            return false           public void pop        if top  lt  0           System out println  stack is empty         else          int temp   stackDatas top           stackDatas   ArrayUtils remove stackDatas  top--           System out println  poped data--- gt    temp            public String toString        String result             if top lt 0           return            else        for int i   0  i lt  size    i             result   result   stackDatas i                         return result substring 0  result lastIndexOf                    calling MyStack       public class CallingMyStack    public static MyStack ms   public static void main String   args         ms   new MyStack        ms push 1       ms push 2       ms push 3       ms push 4       ms push 5       ms push 6       ms push 7       ms push 8       ms push 9       ms push 10       System out println  size    MyStack size         System out println  List--- gt    ms       System out println  ----------        ms pop        ms pop        ms pop        ms pop        System out println  List--- gt    ms       System out println  size    MyStack size             output   size  10 List--- gt   1 2 3 4 5 6 7 8 9 10  ---------- poped data--- gt  10 poped data--- gt  9 poped data--- gt  8 poped data--- gt  7 List--- gt   1 2 3 4 5 6  size  6

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