Deep compare sets in Java

Question

I have two sets in Java that compare Item objects. Is there a method to compare the sets so that Item\'s equals method is invoked and

Answer 1

This is the default behaviour, if it's not what you're seeing then check that you're overriding hashCode as well. See the following code for an example:

public static void main(String[] args) {
    Set items1 = new HashSet();
    items1.add(new Item("item 1"));
    items1.add(new Item("item 2"));

    Set items2 = new HashSet();
    items2.add(new Item("item 1"));
    items2.add(new Item("item 2"));

    System.out.println(items1.equals(items2));
}

private static class Item {
    private String id;

    public Item(String id) {
        this.id = id;
    }

    @Override
    public int hashCode() {
        return id.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        return id.equals(((Item)obj).id);
    }
} 

This outputs:

true