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copied!<p>If you are coming from Java, it can sound strange at first (it was the same for me), but actually now I find it's more regular syntax then Java's, where I need to explicitly say whether I want to <code>implement</code> or <code>extend</code> other class/interface. But I think it's more question of the personal taste. </p> <p>It does not actually matter whether you are saying <code>extends</code> or <code>implements</code>. They both represent the same kind of relationship between two things: <strong>is a</strong> (in contrast to delegation and composition, which represent <strong>has a</strong> relationship). Here, for instance, you can find some more information about it:</p> <p><a href="http://www.javacamp.org/moreclasses/oop/oop5.html" rel="nofollow">http://www.javacamp.org/moreclasses/oop/oop5.html</a></p> <p>Just try to replace <code>extends</code>, <code>implements</code>, <code>with</code> with <code>is a</code> and it becomes more clear. </p> <p>In Scala you also have other variations of <code>is a</code> relation. For example <strong>self types</strong>:</p> <pre><code>trait Bar { self: Foo => // ... } </code></pre> <p>With this you are saying, that <code>Bar</code> does not extends/implements <code>Foo</code> directly, but all other classes, that want to extend <code>Bar</code> should also extend <code>Foo</code>. </p> <p><strong>Self types</strong> can allow interesting things. For example two classes/traits that depend on each other:</p> <pre><code>class Bar extends Foo { def sayHello(name: String) = println("Hello, " + name) greet() } trait Foo { this: Bar => def greet() = sayHello("User") } new Bar() // prints: Hello, User </code></pre>

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