Why Do I Get a ClassCastException When Casting an Object Array to an Integer Array in Java?

Casting Object Array to Integer Array: A ClassCastException Conundrum

In the realm of Java programming, casting an array of one type to another can often lead to confusion, especially when dealing with arrays of primitives and objects. Let's take a closer look at the following code snippet:

<code class="java">Object[] a = new Object[1];
Integer b = 1;
a[0] = b;
Integer[] c = (Integer[]) a;</code>

When attempting to execute this code, you may encounter a ClassCastException at the last line. Why is this so?

The issue lies in the incompatible types of the arrays. Integer[] is a subtype of Object[], meaning that an array of Integers can be safely assigned to an array of Objects. However, the converse is not true. Object[] cannot be treated as Integer[].

To rectify this issue, you cannot simply cast the Object array to an Integer array. Instead, you can utilize the Arrays.copyOf() or Arrays.copyOfRange() methods to explicitly create a new Integer array with the desired contents.

<code class="java">// Using Arrays.copyOf()
Integer[] integerArray = Arrays.copyOf(a, a.length, Integer[].class);

// Using Arrays.copyOfRange()
Integer[] integerArray = Arrays.copyOfRange(a, 0, a.length, Integer[].class);</code>

Alternatively, you can declare an array of Integers from the outset and assign it to the Object array:

<code class="java">Object[] a = new Integer[1];
Integer b = 1;
a[0] = b;</code>

In this scenario, no ClassCastException will occur.

Thus, to successfully cast an Object array to an Integer array, it's imperative to utilize the appropriate methods or ensure that the Object array contains only Integers.

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