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    <p>If your code has "key = null;" right before the test of instanceof, then the Exception will necessarily be thrown. </p> <p>The reason being that the instancof operator checks the reference of the type of object being pointed to and not how it is declared to be.</p> <p>You can try with this simple example and remove the comments accordingly to see the difference:</p> <pre><code>public static void main(String[] args) { //Object obj = new Integer(9); Object obj = null; if (!(obj instanceof Integer)) System.out.println("Not Integer."); else System.out.println("Is Integer"); } </code></pre> <p>Also, you can find out more details here:</p> <p><a href="http://download.oracle.com/javase/tutorial/java/nutsandbolts/op2.html" rel="nofollow">http://download.oracle.com/javase/tutorial/java/nutsandbolts/op2.html</a></p> <p>Hope it helps :)</p> <hr> <p>Full blown example of Java Generics:</p> <pre><code>class GenTest&lt;Key extends Integer, Value&gt;{ Key key; Value val; GenTest(Key key, Value val){ this.key = key; this.val = val; System.out.println("Key: " + key + " Value: " + val); } } public class GenericRecap { public static void main(String[] args) { //Object obj = new Integer(9); Object obj = null; if (!(obj instanceof Integer)) System.out.println("Not Integer."); else System.out.println("Is Integer"); new GenTest&lt;Integer, String&gt;(9, "nine"); //new GenTest&lt;String, String&gt;("funny", "nine"); // In-Error } } </code></pre> <p>Also note that by having 'Key extends Integer', an exception will be thrown during Runtime if you pass that does not subclass Integer. Furthermore, if you're using and IDE that checks for it, it'll be flag as 'Type not within bound' of the GenTest Class.</p> <p>Floats and Integer all inherit from Number. Thus you can 'extend Number' and then check for 'instanceof Integer' or 'instanceof Float' depending on how you want to use it in your code.</p> <p>Hope it helps :) Cheers!</p>
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    1. POJava: Check if a generic is an int
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    1. COOk. But if I don't initialize it to null, the compiler says that I have to initialize it. And I can't assign it any value because it's a generic! How can I do this check then?
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    2. COassigning values has nothing to do with it being `Generic`, I don't think you understand what `Generic` does
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    3. COI see your point. I assigned it null just because the IDE forced me to do it. If that approach is not valid at all in your opinion, what's the proper way to check if the Generic that has been passed is an int?
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