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Exploring java.lang >
Siva Nookala - 01 Apr 2016
java.lang.Class is a Class extends Object class and implements Serializable, GenericDeclaration, Type, AnnotatedElement. Class represents the classes and interfaces running in a Java application.

Declaration of Class:
The declaration of Class is shown below.
public final class Class<T> extends Object implements Serializable, GenericDeclaration, Type, AnnotatedElement
Here, T represents the type of class modeled by the Class object. For example, the type of String.class is Class<String>. Use Class<?> if the class being modeled is unknown.
Class has no public constructor. Instead Objects of type Class are created automatically by the Java Virtual Machine, when classes are loaded. Gnerally, we obtain a Class object by calling the getClass() method defined by Object class.

Class methods:
MethodDescription
static Class<?>forName(String name)
throws ClassNotFoundException
Returns a class object given its complete name .
Annotations[]getAnnotaions() Obtains all Annotations associated with the invoking object and stores them in an array of Annotations objects.Returns a reference to this array .
String getName()Returns the complete name of the class or interface of the object.
String toString()Returns the string representation of the invoking object or interface.
boolean isInterface()Returns true if the invoking object is an interface . Otherwise,it returns false.

class
class sample
{
    public static void main(String arg[])
    {
        X x = new X();
        Y y = new Y();
        Class<?> clObj; // LINE A
        clObj = x.getClass();
        System.out.println("X is object of class : " + clObj.getClass()); // LINE B
        /*if (clObj.equals(x))
        {
            System.out.println("clObj and x are the references of same class");
        }
        else
        {
            System.out.println("clObj and x are the references of two different classes");
            System.out.println("clObj is a reference of " + clObj.getClass() + " and x is the reference of " + x.getClass());
        }*/
        clObj = y.getClass();
        System.out.println("Y is object of type : " + clObj.getName()); // LINE C
        clObj = clObj.getSuperclass();
        System.out.println("Y's Superclass is  " + clObj.getName()); // LILNE D    
    }
}

class X
{
    int a;
    float b;
}

class Y extends X
{
    double c;

}
OUTPUT

X is object of class : class java.lang.Class
Y is object of type : Y
Y's Superclass is  X

DESCRIPTION

In the above program we have demonstrated the usage of methods getClass, getName and getSuperClass of java.langa.Class. Firstly we have created two objects one for class X and other for class Y. At LINE A we have created a reference clObj of class java.lang.Class and referenced it to java.lang.Class using getClass() and we have printed it at LINE B and at LINE C we are printing the class name of the clObj reference. At LINE D we are referencing clObj to X by using getSuperclass method. and printed it.

THINGS TO TRY
  • After LINE B uncomment the code and see the output.
    The output will be clObj and x are the references of two different classes
    clObj is a reference of class java.lang.Class and x is the reference of class com.java.lang.X
  • Try for the belwo code.
    Integer i = 10;
    System.out.println(i.getClass());
    The output should be class java.lang.Integer
    Remember primitive Java types ( boolean, byte, char, short, int, long, float, and double), and the keyword void are also represented as Class objects.

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