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    <p>In most cases, you should use the <code>instanceof</code> operator to test whether an object is an array.</p> <p>Generally, you test an object's type before downcasting to a particular type which is known at compile time. For example, perhaps you wrote some code that can work with a <code>Integer[]</code> or an <code>int[]</code>. You'd want to guard your casts with <code>instanceof</code>:</p> <pre><code>if (obj instanceof Integer[]) { Integer[] array = (Integer[]) obj; /* Use the boxed array */ } else if (obj instanceof int[]) { int[] array = (int[]) obj; /* Use the primitive array */ } else ... </code></pre> <p>At the JVM level, the <code>instanceof</code> operator translates to a specific <a href="http://java.sun.com/docs/books/jvms/second_edition/html/Instructions2.doc6.html#instanceof" rel="nofollow noreferrer">"instanceof"</a> byte code, which is optimized in most JVM implementations.</p> <p>In rarer cases, you might be using reflection to traverse an object graph of unknown types. In cases like this, the <code>isArray()</code> method can be helpful because you don't know the component type at compile time; you might, for example, be implementing some sort of serialization mechanism and be able to pass each component of the array to the same serialization method, regardless of type.</p> <p>There are two special cases: null references and references to primitive arrays.</p> <p>A null reference will cause <code>instanceof</code> to result <code>false</code>, while the <code>isArray</code> throws a <code>NullPointerException</code>.</p> <p>Applied to a primitive array, the <code>instanceof</code> yields <code>false</code> unless the component type on the right-hand operand exactly matches the component type. In contrast, <code>isArray()</code> will return <code>true</code> for any component type.</p>
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    1. COYeah, but how much difference is it going to make? That sounds like a micro-optimization to me.
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      1. USMichael Myers
    2. COIt depends on the application, but I'd be surprised to find the difference large enough to be worth going out of your way for. But, since it's the conventional approach, you should have some special reason (like support for primitive arrays) to justify using the awkward, sub-optimal reflection.
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    3. CO`instanceof` won't work with arrays of integral types.
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