Java Reflection API | Java.lang.Class

ref: http://www.studytonight.com/java/reflection-api

Reflection API

reflection means ability of a software to analyze itself. In java, Reflection API provides facility to analyze and change runtime behavior of a class, at runtime

For Example, using reflection at the runtime you can determine what method or modifiers a class supports

 

What is reflect package ?

java.lang.reflect package encapsulates serveral important interface and classes. These classes and interface define methods which are used for reflection

 

 class　　　　　　　　　　　　description

----------------------------------------------------------------------------------------------------------

Array　　　　　　　　　　　　allow you to dynamically created and manipulate arrays

Constructor　　　　　　　　　gives info abt constructor of a class

Field　　　　　　　　　　　　  provides info abt field

Method　　　　　　　　　　　 procide info abt method

Modifier　　　　　　　　　　　provide info abt class and member access modifier

Proxy　　　　　　　　　　　　 supports dynamic proxy classes

 

java.lang.Class is another important class used in Reflection API

 

 

Uses of Reflection

1. Developing IDE
2. Debugging and Test tools

3. Loading drivers and providing dynamic info

 

Disadvantages of Reflection

1. Low performance

2. Security risk

3. Violation of OOPs concept

 

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Reflection Class

 

java.lang.Class 

Class is a final class injava.lang package which extends Object class. Instance of this class 

represents classes and interfaces in a running java application. It is used to analyze and change dynamic behavior of a class at runtime

 

Some Important Methods of java.lang.Class class

This class defines several methods using which we can get info about methods, constructors, modifiers and members of a class at runtime

forName()　　　　

1. this method takes fully qualified name of classes or nterfaces as its argument and return instance 

   of the class associated with it. 

2. static Class<?> forName(String className)

class Student{}
class Test
{
 public static void main(String args[])
 {
  Class c = Class.forName("Student");
  System.out.println(c.getName());
 }
}
output: Student

getConstructors() and getDeclaredConstructors()

1. getConstructors() returns array of Constructors object that represent all the public constructors of the invoking object. This method only returns public constructor. getDeclaredConstructors() will return all constructors

Constructor< ?>[] getConstructors();
Constructor< ?>[] getDeclaredConstructors();

Example using getConstructors() and getDeclaredConstructors() method

Class c = Class.forName("Student");
  Constructor< Student>[] ct = c.getConstructors();
  for(int i=0; i< ct.length; i++)
    { System.out.println(ct[i]); }
  Constructor< Student>[] cdt = c.getDeclaredConstructors();
  for(int i=0;i< cdt.length;i++)
    { System.out.println(cdt[i]);}

output:

  public Student()
  public Student()
  Student(java.lang.String)

getMethods() and getDeclaredMethods()

getFields() and getDeclaredFields()

Example using getFields() and getDeclaredFields() method