Question

I have a vector of entries. Each entry is an instance of this class:

public class Entry implements Comparable<Entry>{

    private String _key;
    private CustomSet _value;

    [...]

    @Override
    public int compareTo(Entry a) {
        return this._key.compareTo(a._key);
    }
}

The vector is declared as shown below:

Vector<Entry> entries = new Vector<Entry>();

After that, the vector is populated. Then I want to check if certain key is somewhere in the vector. So I do this:

Entry sample = new Entry(key, new CustomSet());
if (entries.contains(sample)) {
    // do something
}

This seems not to work. Why? How can I get it to work?

P.S. CustomSet is another user defined class, irrelevant from my point of view

Answer 1

You have to redefine the equals method in your Entry class, because that’s what contains relies in to determine if an element belongs to a collection, as the docs say:

Returns true if this vector contains the specified element. More
formally, returns true if and only if this vector contains at least
one element e such that (o==null ? e==null : o.equals(e)).

In this case o is contain‘s method parameter.