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    <p>The main difference between Java and C++ is the fact that in Java every function is <code>virtual</code>.</p> <p>Historically when C++ have been developed the fact of placing an abastraction layer between every function call (that is what happens using a virtual method table) wasn't something you did want for every method call because a virtual method invocation is slower.</p> <p>So what happens is that you must specify that a method must be called through <a href="http://en.wikipedia.org/wiki/Dynamic_dispatch" rel="nofollow"><strong>dynamic binding</strong></a>, otherwise the method is chosen during compile time according to the declaration of the variable. This means that if you declare <code>Base *b = new Derived()</code> and you call a method on <code>b</code> which is not virtual then method is chosen at compile time and it will be a <code>Base::method</code>.</p> <p>The motto is <em>you don't pay for what you don't use</em> and that's it.</p> <p>Interfaces in C++ doesn't exist, but you can have a class with just pure virtual functions which behave basically in the same way. Actually you can have two kind of virtual methods:</p> <pre><code>class Base { virtual void method() { //implementation } virtual void pureMethod() = 0; } </code></pre> <p>First <code>method()</code> is virtual and obeys to dynamic binding but it is implemented even in Base class while <code>pureMethod()</code> still obeys to dynamic binding but it's declared as pure virtual so it doesn't have any implementation, thus <code>Base</code> cannot be instantiated as it is and you need to subclass it and override at least the pure virtual method.</p>
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