Java Reflection is a process of examining or modifying the run time behavior of a class at run time.
The java.lang.Class class provides many methods that can be used to get metadata, examine and change the run time behavior of a class.
The java.lang and java.lang.reflect packages provide classes for java reflection.
Where it is used
The Reflection API is mainly used in:
- IDE (Integrated Development Environment) e.g. Eclipse, MyEclipse, NetBeans etc.
- Debugger
- Test Tools etc.
java.lang.Class class
The java.lang.Class class performs mainly two tasks:
- provides methods to get the metadata of a class at run time.
- provides methods to examine and change the run time behavior of a class.
How to get the object of Class class?
There are 3 ways to get the instance of Class class. They are as follows:
- forName() method of Class class
- getClass() method of Object class
-
the .class syntax
1) forName() method of Class class - is used to load the class dynamically.
- returns the instance of Class class.
- It should be used if you know the fully qualified name of class.This cannot be used for primitive types.
Let's see the simple example of forName() method.
class Simple{}
class Test{
public static void main(String args[]){
Class c=Class.forName("Simple");
System.out.println(c.getName());
}
} 2) getClass() method of Object class
It returns the instance of Class class. It should be used if you know the type. Moreover, it can be used with primitives.
class Simple{}
class Test{
void printName(Object obj){
Class c=obj.getClass();
System.out.println(c.getName());
}
public static void main(String args[]){
Simple s=new Simple();
Test t=new Test();
t.printName(s);
}
} 3) The .class syntax
If a type is available but there is no instance then it is possible to obtain a Class by appending ".class" to the name of the type.It can be used for primitive data type also.
class Test{
public static void main(String args[]){
Class c = boolean.class;
System.out.println(c.getName());
Class c2 = Test.class;
System.out.println(c2.getName());
}
} Determining the class object
Following methods of Class class is used to determine the class object:
- public boolean isInterface(): determines if the specified Class object represents an interface type.
- public boolean isArray(): determines if this Class object represents an array class.
- public boolean isPrimitive(): determines if the specified Class object represents a primitive type.
Let's see the simple example of reflection api to determine the object type.
class Simple{}
interface My{}
class Test{
public static void main(String args[]){
try{
Class c=Class.forName("Simple");
System.out.println(c.isInterface());
Class c2=Class.forName("My");
System.out.println(c2.isInterface());
}catch(Exception e){System.out.println(e);}
}
}