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POWhat's the advantage of having public static inner classes of an interface/class?
 

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  1. POWhat's the advantage of having public static inner classes of an interface/class?
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    <p>I've noticed the following code pattern while browsing through some sources of my project's 3rd party libraries:</p> <pre><code>public interface MyInterface { public static class MyClass1 implements MyInterface { ... } public static class MyClass2 implements MyInterface { ... } public static class MyClass3 implements MyInterface { ... } } </code></pre> <p>Or this one:</p> <pre><code>public class MyBaseClass { public static class MyClass1 extends MyBaseClass { ... } public static class MyClass2 extends MyBaseClass { ... } public static class MyClass3 extends MyBaseClass { ... } } </code></pre> <p>Real life examples:</p> <ul> <li>SwingX: <code>org.jdesktop.swingx.decorator.HighlightPredicate</code> (<a href="http://www.koders.com/java/fidEB3B3E97DBA1FAF92BB26EA66E04D92173575899.aspx?s=idef:sort" rel="noreferrer">Source</a>)</li> <li>Substance: <code>org.pushingpixels.substance.api.renderers.SubstanceDefaultTableCellRenderer</code> (<a href="http://www.koders.com/java/fid8C646B2858A9AD08F3718E0CC08B62386C23CC24.aspx" rel="noreferrer">Source</a>)</li> </ul> <p>What's the advantage of having a code structure like this? </p> <p>My first thought was "aggregation", but the same thing could be achieved using plain old packages. So when/why is it better to use public inner classes instead of a package?</p>
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    1. USDaniel Rikowski
    1. USDaniel Rikowski
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    1. COI didn't look at the real life examples you have posted, but one difference is that the inner classes might use private members of the outer class, which is not the case if they were 'siblings' (separate top-level classes)
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      1. USGrzegorz Oledzki
    2. COGood question. Personally I'd recommend avoiding this pattern as it hides away public classes in a location that people don't generally expect to find them, without providing any obvious benefit for the trade-off. But maybe someone else knows what the benefit of this pattern is supposed to be.
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      1. USaroth
    3. CO@Grzegorz, interfaces can't have private members.
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      1. USPéter Török
 

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