Java Reflection API

Java Reflection API is a process of modifying or retrieve metadata of a class at run time.

The java.lang.Class class provides methods that can be used to get metadata and change the run time behavior of a class.

The java.lang and java.lang.reflect packages are providing classes for java reflection.

The Java Reflection API is using mainly as follows.

1. IDE Development (Example: Eclipse, Myeclipse, Netbeans etc…)
2. Testing Tools
3. Debugger Tools

How to create Object of java.lang.Class?

• Java.lang.Class provides methods to get metadata at a class runtime.
• Java.lang.Class provides methods to change the runtime behavior of the class.

There are 3 ways to create the Instance of the Class class

1. forName() method of Class class
2. getClass() method of Object class
3. the .class syntax

forName() method of Class class

• It is used to load the Class dynamically
• It retruns instance of the Class
• It should be used, if we know the fully qaulified class name
• It can not be used for primitive types

Example :

package com.samples;

public class NTutorial{

}

package com.samples;

public class Tutorial{

public static void main(String args[]) throws ClassNotFoundException{

Class c=Class.forName("com.samples.NTutorial");

System.out.println("Class name:"+c.getName());

}

}

Output

Class name:com.samples.NTutorial

getClass() method of Object class

• It returns the instance of Class class.
• It should be used if you know the type.
• It can be used with primitives.

Example :

package com.samples;

public class NTutorial{

}

package com.samples;

public class Tutorial{

public void display(Object obj){

Class cls=obj.getClass();

System.out.println("Class Name:"+cls.getName());

}

public static void main(String args[]) {

NTutorial nt=new NTutorial();

Tutorial t=new Tutorial();

t.display(nt);

}
}

Output

Class Name: NTutorial

the .class syntax

• It can be used like appending “.class” to type as follows in the example
• It can be used for primitive data type also.

Example :

public class Tutorial{

public static void main(String args[]) {

Class c1=boolean.class;

Class c2=int.class;

Class c3=char.class;

Class c4=double.class;

Class c5=Tutorial.class;

System.out.println(c1.getName());

System.out.println(c2.getName());

System.out.println(c3.getName());

System.out.println(c4.getName());

System.out.println(c5.getName());

 

}
}

Output

boolean
int
char
double
Tutorial