What Is java.lang.Class Class

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∟What Is java.lang.Class Class

This section describes what is java.lang.Class class - A built-in class that represent instances of all data types used in a Java application in the JVM.

What Is java.lang.Class Class? java.lang.Class is a built-in class that represent instances of all data types used in a Java application in the JVM. Instances of classes, interfaces, enumerations, annotations, arrays, primitives and void are all represented Class objects.

To access the Class object of a data type, you can use the class literal - the name of a class, interface, array, or primitive type followed by a `.' and the token "class". For example:

Class c = String.class;
Class c = Iterable.class;
Class c = byte[].class;
Class c = int.class;
Class c = void.class;

The Class class offers a set of methods to help to determine if the given Class object represents a specific group of data type:

boolean isAnnotation() - Returns true if this Class object represents an annotation type.
boolean isArray() - Determines if this Class object represents an array class.
boolean isEnum() - Returns true if and only if this class was declared as an enum in the source code.
boolean isInterface() - Determines if the specified Class object represents an interface type.
boolean isPrimitive() - Determines if the specified Class object represents a primitive type.

Here is tutorial example program showing you how to use the class literal and these isXXX() methods:

/* ClassDataType.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
class ClassDataType {
   public static void main(String[] a) {
      java.io.PrintStream out = System.out;
      Class c = null;

      c = String.class;
      out.println(c.getName()+" isLocalClass: "+c.isLocalClass());

      c = java.util.Iterator.class;
      out.println(c.getName()+" isInterface: "+c.isInterface());

      c = Thread.State.class;
      out.println(c.getName()+" isEnum: "+c.isEnum());

      c = Override.class;
      out.println(c.getName()+" isAnnotation: "+c.isAnnotation());

      c = byte[].class;
      out.println(c.getName()+" isArray: "+c.isArray());

      c = String[].class;
      out.println(c.getName()+" isArray: "+c.isArray());

      c = int.class;
      out.println(c.getName()+" isPrimitive: "+c.isPrimitive());

      c = void.class;
      out.println(c.getName()+" isPrimitive: "+c.isPrimitive());
   }
}

When executed, I got this result:

herong> java ClassDataType

java.lang.String isLocalClass: false
java.util.Iterator isInterface: true
java.lang.Thread$State isEnum: true
java.lang.Override isAnnotation: true
[B isArray: true
[Ljava.lang.String; isArray: true
int isPrimitive: true
void isPrimitive: true