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copied!<p><strong>@Override</strong></p> <p>@Override was introduced in Java 5 (and extended a little bit in Java 6). It's only informative. It says "I'm suppose to override something that already exist in parent class or interface.</p> <p>IDE's like Eclipse can warn you in case there's no such parent method (by example if you mispell the name). In that case your method will not be invoked (because of the mispelling).</p> <p>But don't worry too much about it.</p> <p><strong>Abstract class vs interface</strong></p> <p>An abstract class allows you define a basic functionality leaving undefined parts. An interface doesn't allow you to implement anything. You can program everything except the part that really changes in each case. So when you need it, you inherit and implement the missing part.</p> <p><strong>Override two methods</strong></p> <p>Yes. In Java you can override all methods not explicity declared as final in parent class. It's ok. If you want to make it unmodifiable you can declare it final. By example, if you want to declare an ordering you could:</p> <pre><code>public abstract class Ordering<X> { abstract boolean isLower(X a, X b); abstract boolean isEquals(X a, X b); final boolean isGreater(X a, X b) { return !isLower(a, b) && !isEquals(a, b); } } </code></pre> <p>Of course it may have sense to override isGreater to implement it another more efficient way (imagine it's costly to compare). But there are scenarios when you want to provide basic already implemented functionality (and then's when abstract classes are better than interfaces) or when you want to force some implementation (then's when final keyword show useful).</p>

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