How to use class literals?

Java language supports dynamic loading of classes (e.g., What does Class.forname("x") method do?). For example, you can use:

   Class c = Class.forName("java.lang.String");

to retrieve a Class object representing the class java.lang.String, which is a special class used to represent classes. There is one Class object for each loaded class known to the Java runtime system.

The class literal is another way to produce the reference to the Class object. For example:

public class literal {
      public static void main(String args[])
      {
         Class c = java.lang.String.class;
         Class c2 = double.class;
         Class c3 = Double.TYPE;
         
         System.out.println(c);
         System.out.println(c2);
         System.out.println(c3);
      }
    }

The class must be known at compile time otherwise a compile error is generated. The output of this program is:

   class java.lang.String
   double
   double

c in the program represents the loaded class java.lang.String, while c2 and c3 represent the primitive data type double. Double is a wrapper class for double, and TYPE a special member within the class that represents its underlying primitive type.

According to specification, Class literals work with regular classes as well as interfaces, arrays, and primitive types. In addition, there is a standard field called TYPE that exists for each of the primitive wrapper classes. The TYPE field produces a reference to the Class object for the associated primitive type (see Inner Classes Specification), such that:

 
        boolean.class   ==   Boolean.TYPE
        char.class      ==   Character.TYPE
        byte.class      ==   Byte.TYPE
        short.class     ==   Short.TYPE
        int.class       ==   Integer.TYPE
        long.class      ==   Long.TYPE
        float.class     ==   Float.TYPE
        double.class    ==   Double.TYPE
        void.class      ==   Void.TYPE

You cannot use a variable with .class. For example:

class Program {
  public static void main(String[] args) {
    int i = 5;
    String s = "Hello";
    
    System.out.println(i.class);  // compile error
    System.out.println(s.class);  // compile error
  }
}

References

15.8.2 Class Literals
Inner Classes Specification

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