Testing java equals and hashcode methods

Posted on October 24, 2009 by Martin Harris

Write a java test for the equals method! What is the point in wasting time on that?

All good java programmers know the equals and hashcode methods are vitally important. I have seen some unpredictable behavior through bugs in these two methods.

If your about to click away to something more interesting fine, but first read my page with an example equals bug. See if you can spot the problem before I show the solution.

Writing a test for the equals method

Writing a test for equals is so easy its tedious. Which is perhaps why so much code gets written and not tested. First from the javadoc what are the specifications for a good equals and hashcode implementations?

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IDE Generation of equals methods has its moments

Posted on October 24, 2009 by Martin Harris

Generating java bugs in equals methods using an IDE

Its no revelation that Eclipse, Netbeans and others can generate code. Its particularly useful if getters, setters or constructors are required. Implementing an interface is very simple indeed as these IDE will stub out the interface methods. More complex methods though require some thought. Generation of the equals method is such a case.

How to write a good equals method is well documented by Joshua Bloch in Effective Java, Chapter 3 by Joshua Bloch.

Eclipse V Netbeans who generates the best code?

Before we get deeper into the code here are two efforts at generating the equals method for this class:

public class SimpleBean  {
    private final BigDecimal bigDecimal;
    public SimpleBean(BigDecimal bigDecimal) {
        this.bigDecimal = bigDecimal;
    }
}