can anyone plz guide me how to override these two=equals() and hashcode () methods?
i never understand how to implement them.can someone plz give an example to show how to override these two..
plz plz i need help on this topic..
thanks

Hi,

You can not override equals method from java.lang.String class since String class is FINAL class.
But you can override equals() method in any other class since all classes are implicitly inherited from Object class which is NOT FINAL.
Following is sample code stored in "testOverriding.java" file. Here equals method is used to display string instead of comparison.

class newequals
{
   public void equals(String str){
     System.out.println(str);
    }
}

public class testOverriding
{
    public static void main(String[] args){
    newequals test = new newequals();
    test.equals("Test String");
    }
}

----------------
OUTPUT
---------------

Test String

1. public class Test
2. {
3. private int num;
4. private String data;
5.
6. public boolean equals(Object obj)
7. {
8. if(this == obj)
9. return true;
10. if((obj == null) || (obj.getClass() != this.getClass()))
11. return false;
12. // object must be Test at this point
13. Test test = (Test)obj;
14. return num == test.num &&
15. (data == test.data || (data != null && data.equals(test.data)));
16. }
17.
18. public int hashCode()
19. {
20. int hash = 7;
21. hash = 31 * hash + num;
22. hash = 31 * hash + (null == data ? 0 : data.hashCode());
23. return hash;
24. }
25.
26. // other methods
27. }

Here's a link to a tutorial (where the preceeding code was taken from): http://www.geocities.com/technofundo...equalhash.html
See the link above for the complete tutorial.

- A.Kahtava

Sorry !!
for my previous post that was example of Overloading I have modified the code below which represents Overriding for equals() and hashcode()

You can not override equals method from java.lang.String class since String class is FINAL class.
But you can override equals() method in any other class since all classes are implicitly inherited from Object class which is NOT FINAL.
Following is sample code stored in "testOverriding.java" file. Here equals method is used to display string instead of comparison.

class BaseMethods
{
   BaseMethods(){
   System.out.println("Constructor called for Base Methods\n");
   }
}

class OveriddenMethods
{
   public void equals(){
    System.out.println("Equals Overridden\n");
   }

   public int hashCode() {
    System.out.println("Hashcode Overridden\n");
    return 100;
   }
}

public class testOverriding
{
  public static void main(String[] args){
   int returnVal =0;
   String s1 = "abcd";
   String s2 = "abcd";

  System.out.println("Base equals method result = " +s1.equals(s2) + "\n");

  BaseMethods base = new BaseMethods();
  returnVal =base.hashCode();
  System.out.println("returnVal = " + returnVal + "\n");

 // equals() and hashCode methods are Overridden below in OveriddenMethods Class

 OveriddenMethods test=new OveriddenMethods();
   test.equals();
   returnVal = test.hashCode();
   System.out.println("returnVal = " + returnVal + "\n");
  }
}

----------------
OUTPUT
---------------
Base equals method result = true

Constructor called for Base Methods

returnVal = 15655788

Equals Overridden

Hashcode Overridden

returnVal = 100
----------------------------------

Thanks,

ARP