Java – casting Object array to Integer array error

castingjava

What's wrong with the following code?

Object[] a = new Object[1];
Integer b=1;
a[0]=b;
Integer[] c = (Integer[]) a;

The code has the following error at the last line :

Exception in thread "main" java.lang.ClassCastException:
[Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer;

Best Answer

Ross, you can use Arrays.copyof() or Arrays.copyOfRange() too.

Integer[] integerArray = Arrays.copyOf(a, a.length, Integer[].class);
Integer[] integerArray = Arrays.copyOfRange(a, 0, a.length, Integer[].class);

Here the reason to hitting an ClassCastException is you can't treat an array of Integer as an array of Object. Integer[] is a subtype of Object[] but Object[] is not a Integer[].

And the following also will not give an ClassCastException.

Object[] a = new Integer[1];
Integer b=1;
a[0]=b;
Integer[] c = (Integer[]) a;

Related Solutions

C# – Direct casting vs ‘as’ operator

string s = (string)o; // 1

Throws InvalidCastException if o is not a string. Otherwise, assigns o to s, even if o is null.

string s = o as string; // 2

Assigns null to s if o is not a string or if o is null. For this reason, you cannot use it with value types (the operator could never return null in that case). Otherwise, assigns o to s.

string s = o.ToString(); // 3

Causes a NullReferenceException if o is null. Assigns whatever o.ToString() returns to s, no matter what type o is.

Use 1 for most conversions - it's simple and straightforward. I tend to almost never use 2 since if something is not the right type, I usually expect an exception to occur. I have only seen a need for this return-null type of functionality with badly designed libraries which use error codes (e.g. return null = error, instead of using exceptions).

3 is not a cast and is just a method invocation. Use it for when you need the string representation of a non-string object.

Java – Create ArrayList from array

new ArrayList<>(Arrays.asList(array));

Best Answer

Related Solutions

C# – Direct casting vs ‘as’ operator

Java – Create ArrayList from array

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