How to determine the primitive type of a primitive variable?

Question

Is there a "typeof" like function in Java that returns the type of a primitive data type (PDT) variable or an expression of operands PDTs?

instanceof seems to work for class types only.

Answer 1

Try the following:

int i = 20; float f = 20.2f; System.out.println(((Object)i).getClass().getName()); System.out.println(((Object)f).getClass().getName()); 

It will print:

java.lang.Integer java.lang.Float 

As for instanceof, you could use its dynamic counterpart Class#isInstance:

Integer.class.isInstance(20);  // true Integer.class.isInstance(20f); // false Integer.class.isInstance("s"); // false 

Answer 2

There's an easy way that doesn't necessitate the implicit boxing, so you won't get confused between primitives and their wrappers. You can't use isInstance for primitive types -- e.g. calling Integer.TYPE.isInstance(5) (Integer.TYPE is equivalent to int.class) will return false as 5 is autoboxed into an Integer before hand.

The easiest way to get what you want (note - it's technically done at compile-time for primitives, but it still requires evaluation of the argument) is via overloading. See my ideone paste.

...  public static Class<Integer> typeof(final int expr) {   return Integer.TYPE; }  public static Class<Long> typeof(final long expr) {   return Long.TYPE; }  ... 

This can be used as follows, for example:

System.out.println(typeof(500 * 3 - 2)); /* int */ System.out.println(typeof(50 % 3L)); /* long */ 

This relies on the compiler's ability to determine the type of the expression and pick the right overload.