Introduction To Reflection In Java

Introduction

In this article, we discuss reflection in Java. Reflection is the process of determining or modifying the behavior of a class at runtime. Java provides a java.lang.Class class that contains many methods, that help in finding metadata and to change the runtime behavior of a class.

What are the uses of Reflection?

It is mainly used in:

Integrated Development Environments (IDEs), for example, Eclipse, MyEclipse, NetBeans etcetera.
Test Tolls
Debugger etcetera.

This class generally used to performs two tasks

they have a method, that is used to find and changes the runtime behavior of a class.
they provide methods, that get the metadata of a class at runtime.

Some Drawbacks of reflection

Performance overhead
Security Restrictions
Exposure of Internals

Some commonly used public methods of the Class class

String getName()
static Class forName(String className) throws ClassNotFoundException
Object newInstnce() throws InstantiationException, IllegealAccessException
boolean isInterface()
boolean isArray()
boolean isPrimitive()
Class getSuperclass()
Field[] getDeclaredFields() throws SecurityException
Method[] getDeclaredMethods() throws SecurityException
Constructor[] getDeclaredConstrutors() throws SecurityException
Method getDeclaredMethod(String name, Class[] parameterTypes) throws NoSuchMethodException, SecurityException

How to determine the Object of the class at runtime

By using forName() method.
By using getClass() method
By using .class syntax

1. Use of the forName() method

Example

class Reflection {}
class Check {
public static void main(String args[]) throws ClassNotFoundException {
Class cls = Class.forName("Reflection");
System.out.println(cls.getName());
}
}

Output

2. By using the getClass() method

Example

class Reflection {}
class Check {
void printName(Object ob) {
Class cls = ob.getClass();
System.out.println(cls.getName());
}
public static void main(String args[]) {
Reflection ref = new Reflection();
Test tst = new Test();
tst.printName(ref);
}
}

Output

3. By using the .class syntax

Example

class Check {
public static void main(String args[]) {
Class cls1 = Check.class;
System.out.println(cls1.getName());
Class cls = boolean.class;
System.out.println(cls.getName());
}
}

Output