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copied!<p>From the <a href="http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html" rel="noreferrer">Java Tutorial</a>:</p> <blockquote> <p>Nested classes are divided into two categories: static and non-static. Nested classes that are declared static are simply called static nested classes. Non-static nested classes are called inner classes. </p> </blockquote> <p>Static nested classes are accessed using the enclosing class name:</p> <pre><code>OuterClass.StaticNestedClass </code></pre> <p>For example, to create an object for the static nested class, use this syntax:</p> <pre><code>OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass(); </code></pre> <p>Objects that are instances of an inner class exist within an instance of the outer class. Consider the following classes:</p> <pre><code>class OuterClass { ... class InnerClass { ... } } </code></pre> <p>An instance of InnerClass can exist only within an instance of OuterClass and has direct access to the methods and fields of its enclosing instance.</p> <p>To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:</p> <pre><code>OuterClass.InnerClass innerObject = outerObject.new InnerClass(); </code></pre> <p>see: <a href="http://download.oracle.com/javase/tutorial/java/javaOO/nested.html" rel="noreferrer">Java Tutorial - Nested Classes</a></p> <p>For completeness note that there is also such a thing as an <a href="https://stackoverflow.com/questions/20468856/is-it-true-that-every-inner-class-requires-an-enclosing-instance">inner class <em>without</em> an enclosing instance</a>:</p> <pre><code>class A { int t() { return 1; } static A a = new A() { int t() { return 2; } }; } </code></pre> <p>Here, <code>new A() { ... }</code> is an <em>inner class defined in a static context</em> and does not have an enclosing instance.</p>

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