<p>According to the Java Language Specification, there is a contract between <code>equals(Object)</code> and <code>hashCode()</code>:</p>

<blockquote>
If two objects are equal according to the <code>equals(Object)</code> method, then calling the <code>hashCode</code> method on each of the two objects must produce the same integer result.
It is not required that if two objects are unequal according to the <code>equals(java.lang.Object)</code> method, then calling the <code>hashCode</code> method on each of the two objects must produce distinct integer results.
However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.
</blockquote>

<p>In order to comply with this contract, those methods should be either both inherited, or both overridden.</p>

<h2>Noncompliant Code Example</h2>

<pre>
class MyClass {    // Non-Compliant - should also override "hashCode()"

  @Override
  public boolean equals(Object obj) {
    /* ... */
  }

}
</pre>

<h2>Compliant Solution</h2>

<pre>
class MyClass {    // Compliant

  @Override
  public boolean equals(Object obj) {
    /* ... */
  }

  @Override
  public int hashCode() {
    /* ... */
  }

}
</pre>