how to delete object with same values from a java list

Question

Say I have an object which has an id: String and name: String field.

If I have an array of these objects, if I use the remove method, since technically the Object pointer is different, the object I want won't get removed.

Ex:

List<ObjectA> newList = new ArrayList<>();
// Objecta1(id: a, name: a)
// Objecta2(id: b, name: b)
// Objecta3(id: b, name: b)
newList.add(objecta1);
newList.add(objecta2);
newList.remove(objecta3); --> will equal false

What is the cleanest way to have remove do this correctly?

I searched around and found that I could use removeIf and do a comparison there. I also could use an Iterator and then compare the fields myself. Just wondering if there is a canonical, clean way of doing it in Java. Thanks.

@Eran -- hey so that's what i was thinking of doing. i was just wondering if that was the cleanest way to structure this? — Shail Patel
– Shail Patel, Commented Jan 26, 2017 at 7:23
Yes, you should use an equals method instead of a custom comparison or something. After all, you're checking if two objects should be considered equal. You should probably override equals anyway; a lot of methods use it. — qxz
– qxz, Commented Jan 26, 2017 at 7:27

Viet · Accepted Answer · 2017-01-26 07:27:25Z

3

Beside the solution override equals, you can do it with java 8:

newList.removeIf(p -> p.getId().equals(objecta3.getId()));

answered Jan 26, 2017 at 7:27

Viet

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xenteros · Accepted Answer · 2017-01-26 07:28:53Z

3

Your object should @Override the equals method.

Add the following to your class:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof ObjectA)) return false;

    ObjectA objectA = (ObjectA) o;

    if (getId() != objectA.getId()) return false;
    return getName() != null ? getName().equals(objectA.getName()) : objectA.getName() == null;

}

@Override
public int hashCode() {
    int result = getId();
    result = 31 * result + (getName() != null ? getName().hashCode() : 0);
    return result;
}

and then:

while(newList.remove(objecta3)){};

edited Jan 26, 2017 at 7:28

answered Jan 26, 2017 at 7:26

xenteros

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