Question

I understand what wrappers are, but from the documentation you seem to be able to get an instance of a Class object of type int. Does this return the wrapper or some sort of Class instance of int? Because it wouldn’t make sense if it did, due to generics and type erasure. Isn’t it true that you can only get Class instances of actual classes not primitives? When they say represent do they mean wrapper of something else?

Here is what the JavaDoc says, and why I’m confused

TYPE

public static final Class TYPE

    The Class instance representing the primitive type int.

    Since:
        JDK1.1

Answer 1

Isn’t it true that you can only get Class instances of actual classes not primitives?

Sort of.

But sometimes you need to have some meta-data for “primitive integer”. For example when looking at the method signature. Then you get a Class[] for the parameters, and you somehow need to differentiate between public void test(Integer x) and public void test(int x).

So to facilitate this, there are special Class instances for the primitive types.

To take this a step further, there is even java.lang.Void.TYPE:

 Class<Void> x = void.class;

Insightful Javadoc:

/**
 * Determines if the specified <code>Class</code> object represents a
 * primitive type.
 *
 * <p> There are nine predefined <code>Class</code> objects to represent
 * the eight primitive types and void.  These are created by the Java
 * Virtual Machine, and have the same names as the primitive types that
 * they represent, namely <code>boolean</code>, <code>byte</code>,
 * <code>char</code>, <code>short</code>, <code>int</code>,
 * <code>long</code>, <code>float</code>, and <code>double</code>.
 *
 * <p> These objects may only be accessed via the following public static
 * final variables, and are the only <code>Class</code> objects for which
 * this method returns <code>true</code>.
 *
 * @return true if and only if this class represents a primitive type
 *
 * @see     java.lang.Boolean#TYPE
 * @see     java.lang.Character#TYPE
 * @see     java.lang.Byte#TYPE
 * @see     java.lang.Short#TYPE
 * @see     java.lang.Integer#TYPE
 * @see     java.lang.Long#TYPE
 * @see     java.lang.Float#TYPE
 * @see     java.lang.Double#TYPE
 * @see     java.lang.Void#TYPE
 * @since JDK1.1
 */
public native boolean isPrimitive();