How to implement the Java comparable interface

Question

I am not sure how to implement a comparable interface into my abstract class  I have the following example code that I am using to try and get my head around it    public class Animal      public String name      public int yearDiscovered      public String population       public Animal String name  int yearDiscovered  String population           this name   name          this yearDiscovered   yearDiscovered          this population   population         public String toString            String s    Animal name     name   nYear Discovered    yearDiscovered   nPopulation    population          return s            I have a test class that will create objects of type Animal however I want to have a comparable interface inside this class so that older years of discovery rank higher than low  I have no idea on how to go about this though

User · Answer

Use a Comparator         public class AnimalAgeComparator implements Comparator lt Animal gt      Override public int compare Animal a1  Animal a2

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Here s the code to implement java comparable interface      adding implements comparable to class declaration public class Animal implements Comparable lt Animal gt        public String name      public int yearDiscovered      public String population       public Animal String name  int yearDiscovered  String population                this name   name          this yearDiscovered   yearDiscovered          this population   population              public String toString                 String s    Animal name       name     nYear Discovered       yearDiscovered     nPopulation      population          return s              Override     public int compareTo Animal other      compareTo method performs the comparisons                return Integer compare this year discovered  other year discovered

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Emp class needs to implement Comaparable interface so we need to Override its compateTo method    import java util ArrayList  import java util Collections    class Emp implements Comparable lt  Emp  gt        int empid      String name       Emp int empid String name            this empid   empid             this name   name                Override     public String toString            return empid     name              Override     public int compareTo Emp o          if this empid  o empid          return 0                else if this empid  lt  o empid        return 1              else         return -1                     public class JavaApplication1         public static void main String   args         ArrayList lt Emp gt  a  new ArrayList lt Emp gt          a add new Emp 10  Mahadev           a add new Emp 50  Ashish           a add new Emp 40  Amit           Collections sort a         for Emp id a         System out println id

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Possible alternative from the source code of Integer compare method which requires API Version 19 is    public int compareTo Animal other        return Integer valueOf this year discovered  compareTo other year discovered      This alternative does not require you to use API version 19

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You just have to define that Animal implements Comparable lt Animal gt  i e  public class Animal implements Comparable lt Animal gt   And then you have to implement the compareTo Animal other  method that way you like it    Override public int compareTo Animal other        return Integer compare this year discovered  other year discovered       Using this implementation of compareTo  animals with a higher year discovered will get ordered higher  I hope you get the idea of Comparable and compareTo with this example

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You need to    Add implements Comparable lt Animal gt  to the class declaration  and Implement a int compareTo  Animal a   method to perform the comparisons    Like this   public class Animal implements Comparable lt Animal gt       public String name      public int year discovered       public String population        public Animal String name  int year discovered  String population           this name   name          this year discovered   year discovered          this population   population             public String toString         String s    Animal name     name   nYear Discovered    year discovered   nPopulation    population       return s              Override     public int compareTo  final Animal o            return Integer compare this year discovered  o year discovered

User · Answer

This thing can easily be done by implementing a public class that implements  Comparable  This will allow you to use compareTo method which can be used with any other object to which you wish to compare   for example you can implement it in this way   public String compareTo Animal oth         return String compare this population  oth population       I think this might solve your purpose

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Implement Comparable lt Animal gt  interface in your class and provide implementation of int compareTo Animal other  method in your class See This Post

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You would need to implement the interface and define the compareTo   method  For a good tutorial go to - Tutorials point link or  MyKongLink

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While you are in it  I suggest to remember some key facts about compareTo   methods   CompareTo must be in consistent with equals method e g  if two objects are equal via equals     there compareTo   must return zero otherwise if those objects are stored in SortedSet or SortedMap they will not behave properly  CompareTo   must throw NullPointerException if current object get compared to null object as opposed to equals   which return false on such scenario    Read more  http   javarevisited blogspot com 2011 11 how-to-override-compareto-method-in html ixzz4B4EMGha3

[java] How to implement the Java comparable interface?

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