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Thread: Problem with equality check with HashSet

  1. #1
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    Question Problem with equality check with HashSet

    below is my java program. Please tell me why i am getting the size of hashset as 2 instead of 1 as i have overridden the equals and hashcode method.


    import java.util.HashSet;
    import java.util.Set;


    public class EqualityCheck {
    String first = new String();
    String second = new String();
    /**
    * @param args
    */
    public static void main(String[] args) {
    // TODO Auto-generated method stub

    EqualityCheck t1 = new EqualityCheck();
    t1.first = "megha";
    t1.second = "jain";

    EqualityCheck t2 = new EqualityCheck();
    t2.first = "j megha";
    t2.second = "jain";

    if(t1.equals(t2)){
    System.out.println("t1 and t2 are equal");
    System.out.println("t1 hashcode"+t1.hashCode());
    System.out.println("t2 hashcode"+t2.hashCode());
    }
    Set<EqualityCheck> set1 = new HashSet<EqualityCheck>();
    set1.add(t1);
    set1.add(t2);
    set1.add(t1);
    System.out.println("set "+set1.toString()+"size = "+set1.size());

    }

    public boolean equals(EqualityCheck t){
    System.out.println("inside equals method");
    return true;
    }

    public int hashCode(){
    System.out.println("inside hashcode method");
    return 1111;
    }

    }

    this is the output i am getting while running this in eclipse.

    inside equals method
    t1 and t2 are equal
    inside hashcode method
    t1 hashcode1111
    inside hashcode method
    t2 hashcode1111
    inside hashcode method
    inside hashcode method
    inside hashcode method
    inside hashcode method
    inside hashcode method
    set [EqualityCheck@457, EqualityCheck@457]size = 2


  2. #2
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    Default Re: Problem with equality check with HashSet

    The exact signature to override the equals method is as below:

    public boolean equals(Object obj){}

  3. #3
    Super Moderator Norm's Avatar
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    Default Re: Problem with equality check with HashSet

    Use the @Override statement to verify correct coding:
    Your code as is with the @Override added gives this compile error:

    EqualityCheck.java:35: method does not override or implement a method from a supertype

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