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POJava generics (template) specialization possible (overriding template types with specific types)
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  1. POJava generics (template) specialization possible (overriding template types with specific types)
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    copied!<p>I'm wondering what are the options to specialize generic types in Java, i.e. in a templated class to have specific overrides for certain types.</p> <p>In my case I was a generic class (of type T) to return null usually, but return "" (the empty string), when T is the String type, or 0 (zero) when its the Integer type, etc.</p> <p>Merely providing a type-specific overload of a method produces a "method is ambiguous" error:</p> <p>e.g.:</p> <pre><code>public class Hacking { public static void main(String[] args) { Bar&lt;Integer&gt; barInt = new Bar&lt;Integer&gt;(); Bar&lt;String&gt; barString = new Bar&lt;String&gt;(); // OK, returns null System.out.println(barInt.get(new Integer(4))); // ERROR: The method get(String) is ambiguous for the type Bar&lt;String&gt; System.out.println(barString.get(new String("foo"))); } public static class Bar&lt;T&gt; { public T get(T x) { return null; } public String get(String x) { return ""; } } } </code></pre> <p>Is the only option to subclass the generic class with a specific type (see StringBar in the following example? </p> <pre><code> public static void main(String[] args) { Bar&lt;Integer&gt; barInt = new Bar&lt;Integer&gt;(); StringBar barString2 = new StringBar(); // OK, returns null System.out.println(barInt.get()); // OK, returns "" System.out.println(barString2.get()); } public static class Bar&lt;T&gt; { public T get() { return null; } } public static class StringBar extends Bar&lt;String&gt; { public String get() { return ""; } } } </code></pre> <p>Is this is the only way, it's a bit of a pain to have to create a subclass for every type I want to specialize instead of an overload of get() in the Bar class.</p> <p>I'm guessing I could check the instanceof in the Bar.get() method, e.g. T get(T t) { if (t instanceof String) return ""; if (t instanceof Integer) return 0; else return null; }</p> <p>However I've been taught to avoid instanceof and use polymorphism when possible.</p>
 

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