JAVA EE: Java Reflection in details and how to get the metadata information of the class

Wednesday, 8 November 2017

Java Reflection in details and how to get the metadata information of the class | Reflection in java

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Java Reflection in details and how to get the metadata information of the class | Reflection in java

Display.java

class Display
{
    private String str;

    public Display()
    {
        str = "Welcome";
    }

    public void method1()
    {
        System.out.println("Inside method1,The string is " + str);
    }

    public void method2(int n)
    {
        System.out.println("\nInside method2,The number is " + n);
    }

    private void method3()
    {
        System.out.println("Private method invoked");
    }
}

ReflectionDemo.java

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

/*
 * A simple Java program to demonstrate the use of reflection.
 */
public class ReflectionDemo
{
    public static void main(String[] args) throws Exception
    {
        /*
         * Creating object whose property is to be checked
         */
        Display displayObj = new Display();

        /*
         * Creating class object from the object using getclass method
         */
        Class<? extends Display> classObj = displayObj.getClass();
        System.out.println("The name of class is " + classObj.getName());

        /*
         * Getting the constructor of the class through the object of the class
         */
        Constructor<? extends Display> constructor = classObj.getConstructor();
        System.out.println("The name of constructor is " + constructor.getName());

        System.out.println("\nThe public methods of class are : ");

        /*
         * Getting methods of the class through the object of the class by using
         * getMethods
         */
        Method[] methodArray = classObj.getMethods();

        /*
         * Printing method names
         */
        for (Method method : methodArray)
        {
            System.out.println(method.getName());
        }

        /*
         * Creates object of desired method by providing the method name and
         * parameter class as arguments to the getDeclaredMethod
         */
        Method method2Obj = classObj.getDeclaredMethod("method2", int.class);

        /*
         * invokes the method at runtime
         */
        method2Obj.invoke(displayObj, 19);

        /*
         * Creates object of the desired field by providing the name of field as
         * argument to the getDeclaredField method
         */
        Field field = classObj.getDeclaredField("str");

        /*
         * Allows the object to access the field irrespective of the access
         * specifier used with the field
         */
        field.setAccessible(true);

        /*
         * Takes object and the new value to be assigned to the field as
         * arguments
         */
        field.set(displayObj, "JAVA");

        /*
         * Creates object of desired method by providing the method name as
         * argument to the getDeclaredMethod
         */
        Method method1Obj = classObj.getDeclaredMethod("method1");

        /*
         * invokes the method at runtime
         */
        method1Obj.invoke(displayObj);

        /*
         * Creates object of the desired method by providing the name of method
         * as argument to the getDeclaredMethod method
         */
        Method method3Obj = classObj.getDeclaredMethod("method3");

        /*
         *  Allows the object to access the method irrespective
         *  of the access specifier used with the method
         */
        method3Obj.setAccessible(true);

        /*
         *  invokes the method at runtime
         */
        method3Obj.invoke(displayObj);
    }

}

Output

The name of class is Display
The name of constructor is Display

The public methods of class are : 
method2
method1
wait
wait
wait
equals
toString
hashCode
getClass
notify
notifyAll

Inside method2,The number is 19
Inside method1,The string is JAVA
Private method invoked