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    <p>Your second example does not result in a compiler warning in my eclipse, nor can I think of a reason why it should. It is therefore my preferred solution.</p> <p>The reason unchecked warnings exist is that ignoring them can cause <em>heap pollution</em>:</p> <p>Ordinary casts are checked, i.e. they result in a <code>ClassCastException</code> if the value is not compatible with the desired type. Unchecked casts do not guarantee that, i.e. they can succeed even if the value is not of the proper type. This can result in a variable holding a value that is not a subtype of its declared type, a condition the Java spec <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.12.2" rel="nofollow">calls</a> "heap pollution". To ensure integrity of the runtime type system, the Java compiler will insert ordinary casts whenever a variable of generic type is used. In the presence of heap pollution, these casts can fail.</p> <p>For instance, the program:</p> <pre><code>static void appendTo(List list) { list.add(1); // unchecked warning } static void printLengths(List&lt;String&gt; strings) { for (String s : strings) { // throws ClassCastException System.out.println(s.length()); } } public static void main(String[] args) throws Exception { List&lt;String&gt; strings = new ArrayList&lt;&gt;(); strings.add("hello"); appendTo(strings); printLengths(strings); } </code></pre> <p>throws a <code>ClassCastException</code> at a line that does not contain a cast in the source code. This is likely to severely confuse most programmers.</p> <p>That is why I recommend to use checked casts whenever possible, either with a non-generic cast, or (in generic code) a reflective cast:</p> <pre><code>class Habitat&lt;T&gt; { private final Class&lt;T&gt; clazz; private List&lt;T&gt; inhabitants; void add(Object o) { inhabitants.add(clazz.cast(o)); } } </code></pre>
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    1. POWhy not simply disable unchecked warnings?
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    1. USPaul Bellora
    1. USmeriton
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    1. COI'm not dealing with a typed list in the example, I have made that more obvious now. My second example does provoke the compiler warning, the third one not. But what did we gain in the third example besides making the compiler happy? Why not simply disable the warning in the compiler settings and keep the code like in my second example?
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      1. USJens Bannmann
    2. COYou're right, the examples don't actually provoke a warning. I will rephrase the question.
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      1. USJens Bannmann
 

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