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POIn Java, is it possible to require implementations of an interface to override Object methods?
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copied!<p>Is it possible to require implementations of an interface to override <code>Object</code> methods?</p> <p>For example, if I have an interface that will commonly be used as keys in <code>HashMap</code>s, I may want to require all implementations of that interface to override the <code>hashCode()</code> and <code>equals()</code> methods.</p> <p>However, if I have the following interface...:</p> <pre><code>public interface MyInterface(){ @Override public int hashCode(); @Override public boolean equals(Object o); } </code></pre> <p>...the following implementation compiles:</p> <pre><code>public class MyImplementation(){ } </code></pre> <p>It does not require a method to override <code>hashCode()</code> or <code>equals()</code>, as it inherits these methods from <code>Object</code>.</p> <p>One approach could be to switch to using an abstract class instead of an interface:</p> <pre><code>public abstract class MyAbstractClass(){ @Override public abstract int hashCode(); @Override public abstract boolean equals(Object o); } </code></pre> <p>Then any class that extends this abstract class is required to override <code>hashCode()</code> and <code>equals()</code>:</p> <pre><code>// doesn't compile - requires implementation of hashCode() and equals() public class MyClass extends MyAbstractClass { } // does compile public class MyClass extends MyAbstractClass { @Override public int hashCode(){ // calculate hashcode } @Override public boolean equals(Object o){ // check equality } } </code></pre> <p>My supposition is that the difference between these is that an abstract class is an <code>Object</code>, so it's below <code>Object</code> in the hierarchy, so all extensions are required to meet the contract in the abstract class. Whereas, interfaces are not <code>Object</code>s, so don't sit in the hierarchy, but any implementation of an interface must be an <code>Object</code>, at which point it inherits the <code>Object</code> methods, and thus satisfies the interface 'contract'.</p> <p>However, back to my original question... is there a way to require implementations of an interface to override <code>Object</code> methods?</p>

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