[Snippet for correct implementation of equals() and hashcode()] http://www.javaranch.com/journal/2002/10/equalhash.html

correct_implementation_equal_hashcode.java

public class Test {
    private int num;
    private String data;

    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        
        if ((obj == null) || (obj.getClass() != this.getClass())) {
            return false;
        }
        
        // object must be Test at this point
        Test test = (Test) obj;
        return num == test.num &&
            (data == test.data || (data != null && data.equals(test.data)));
    }

    public int hashCode() {
        int hash = 7;
        hash = 31 * hash + num;
        hash = 31 * hash + (null == data ? 0 : data.hashCode());
        return hash;
    }

    // other methods
}