HashSet does not seem to realize that two objects are the same.

You need to override the Object#hashCode() method in the Move class to let it return the same hashCode() value for the state of the Move instance. Don't forget to override Object#equals() as well.

See also:

  • Overriding equals and hashCode in Java

Hint: if you're using an IDE like Eclipse, you can also just autogenerate them. Rightclick somewhere the Move class, choose Source > Generate hashCode() and equals(). Here is how it look like then:

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + move1;
    result = prime * result + move2;
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Move other = (Move) obj;
    if (move1 != other.move1)
        return false;
    if (move2 != other.move2)
        return false;
    return true;
}

You have to override equals() and hashCode().

This may be an option.

import static java.lang.System.out;
public class Move {
    private int move1;
    private int move2;

    Move(int m1, int m2) {
        move1 = m1;
        move2 = m2;
    }

    public String toString() {
         return String.valueOf(move1)+" "+String.valueOf(move2);
    }

    public int hashCode() {
        return move1 * 31 + move2 * 31;
    }
    public boolean equals( Object other ) {
        if( this == other ) { return true; }
        if( other instanceof Move ) {
            Move m2 = ( Move ) other;
            return this.move1 == m2.move1 && this.move2 == m2.move2;
        }
        return false;
    }

    public static void main( String  [] args ) {
        out.println( new Move(2,3).equals( new Move(2,3)));
        out.println( new Move(1,1).hashCode() == new Move(1,1).hashCode()  );
    }
}

You have to define if the order of the move is relevant ( 1,2 isequals to 2,1 or not )

For more information:

What issues should be considered when overriding equals and hashCode in Java?


HashSet will determine equality based on calling hashCode() and equals(). You have not implemented these, so you'll inherite them from Object. The hashCode and equals methods of Object is just based on whether the references are equal.

That's why if(move1.hashCode()==new Move(t,s).hashCode()) is false. move1 is a different instance than the instance created by calling new Move(t,s).hashCode()

You'll need to implement hashCode and equals in your Move class.

e.g.(though perhaps non-optimal, and you might want a null safe equals - have your IDE generate them if it can)

public int hashCode() {
    return move1 ^ move2 +;
}

public boolean equals(Object o) {
  if(!other instanceof Move) 
      return false;

  Move other = (Move)o;

  return other.move1 == move1 && other.move2 == move2;
}

Tags:

Java

Hashset

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