how to subtract ArrayList using removeall() in java?

Question

I have array list in java:

List<Correction> Auv=new ArrayList<>();
List<Correction> Produv=new ArrayList<>();

then I want to substract Produv value by Auv, here's an example:

Produv.add(new Correction("a","b"));
Produv.add(new Correction("a","c"));
Produv.add(new Correction("b","d"));
Produv.add(new Correction("b","c"));

Auv.add(new Correction("c","a"));
Auv.add(new Correction("b","c"));

Produv.removeall(Auv);

but nothing subtracted, the array still contain it initial value, is there any way to do this? I try to override equals(), and still got the same result

here the code of my Correction class:

    public class Correction {
    private String node0;
    private String node1;

    public Correction(String node0, String node1) {
        this.node0 = node0;
        this.node1 = node1;
    }

    public void setNode0(String node0){
        this.node0=node0;
    }
    public void setNode1(String node1){
        this.node1=node1;
    }

    public String getNode0(){
        return node0;
    }
    public String getNode1(){
        return node1;
    }

    @Override
    public boolean equals(Object object){
        boolean same = false;

        if (object != null && object instanceof Correction)
        {
            same = this.node0 == ((Correction) object).node1 && this.node1 == ((Correction) object).node1;
        }

        return same;
    }
}

Solved!! it just simply a mistake on overriding equals() method(thank's guys) here my correction:

   @Override
    public boolean equals(Object object){
        boolean same = false;

        if (object != null && object instanceof Correction)
        {
            same = (this.node0 == ((Correction) object).node1 && this.node1 == ((Correction) object).node0)||(this.node0 == ((Correction) object).node0 && this.node1 == ((Correction) object).node1);
        }

        return same;
    }

Should this.node0 be equal to object.node1 or object.node0? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jan 14, 2015 at 19:57
Looks like mostly a simple typo to me. (Besides comparing strings.) However, I'll add that Correction overrides equals but does not override hashCode(), which is poor practice. — markspace
– markspace, Commented Jan 14, 2015 at 19:59

Eran · Accepted Answer · 2015-01-14 20:13:56Z

2

Your equals method looks wrong. It makes more sense to compare this.node0 to ((Correction) object).node0.

I think it should be:

public boolean equals(Object object){
    boolean same = false;

    if (object != null && object instanceof Correction)
    {
        same = this.node0.equals(((Correction) object).node0) && this.node1.equals(((Correction) object).node1);
    }

    return same;
}

Also, is this a typo?

Auv.add("c","a");
Auv.add("b","c");

It should probably be :

Auv.add(new Correction ("c","a"));
Auv.add(new Correction ("b","c"));

edited Jan 14, 2015 at 20:13

answered Jan 14, 2015 at 19:58

Eran

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