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POType-safe varargs method that initialises a Map
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  1. POType-safe varargs method that initialises a Map
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    copied!<p>I'm wanting to write a method that I can use to initialise a Map. First cut:</p> <pre><code>Map map(Object ... o) {for (int i = 0; i &lt; o.length; i+=2){result.put(o[i], o[i+1])}} </code></pre> <p>Simple, but not type-safe. Using generics, maybe something like:</p> <pre><code>&lt;TKey, TValue&gt; HashMap&lt;TKey, TValue&gt; map(TKey ... keys, TValue ... values) </code></pre> <p>but that syntax isn't supported. So eventually I come to this:</p> <pre><code>public static &lt;TKey, TValue, TMap extends Map&lt;? super TKey, ? super TValue&gt;&gt; TMap map(TMap map, Pair&lt;? extends TKey, ? extends TValue&gt; ... pairs) { for (Pair&lt;? extends TKey, ? extends TValue&gt; pair: pairs) { map.put(pair.getKey(), pair.getValue()); } return map; } public static &lt;TKey, TValue&gt; HashMap&lt;? super TKey, ? super TValue&gt; map(Pair&lt;? extends TKey, ? extends TValue&gt; ... pairs) { return map(new HashMap&lt;TKey, TValue&gt;(), pairs); } public static &lt;TKey, TValue&gt; Pair&lt;TKey, TValue&gt; pair(TKey key, TValue value) { return new Pair&lt;TKey, TValue&gt;(key, value); } public static final class Pair&lt;TKey, TValue&gt; { private final TKey key; private final TValue value; Pair(TKey key, TValue value) {this.key = key; this.value = value; } public TKey getKey() {return key;} public TValue getValue() {return value;} } </code></pre> <p>But when I try it out, I need to cast it:</p> <pre><code>private static final Map&lt;? extends Class&lt;? extends Serializable&gt;, ? super TypeHandler&lt;? extends Serializable &gt; &gt; validCodeTypes = /* (Map&lt;? extends Class&lt;? extends Serializable&gt;, ? super TypeHandler&lt;? extends Serializable &gt;&gt;) */ map( pair(Integer.class, new IntHandler()), pair(Integer.TYPE, new IntHandler()), pair(Character.class, new CharHandler()), pair(Character.TYPE, new CharHandler()), pair(String.class, new StringHandler()) ); private interface TypeHandler&lt;TType extends Serializable&gt; {} private static class CharHandler implements TypeHandler&lt;Character&gt; {} private static class IntHandler implements TypeHandler&lt;Integer&gt; {} private static class StringHandler implements TypeHandler&lt;String&gt; {} </code></pre> <p>Can anyone tell me how to code my map() methods so that it is entirely general yet doesn't need to be casted?</p>
 

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