Accessing Private Members using Java Reflection PRO

Using the Java Reflection API we can access private members from outside the scope of the class they belong to. When the private member is a field we can even change its value and when the private member is a method we can even indirectly invoke it.

The AcceesibleObject class is the base class for Method, Field and Constructor. The AccessibleObject class provides the ability to flag a reflected object and suppress default Java language access control checks. Flagging a reflected object is done by calling the setAccessible method that was defined in the AccessibleObject class. The following code shows that.

package com.abelski.samples;

import java.lang.reflect.*;

public class Demo
{
 public static void main(String[] args) throws
      SecurityException, NoSuchFieldException, NoSuchMethodException, 
      IllegalAccessException, InvocationTargetException, IllegalArgumentException
 {
  Book book = new Book();
  System.out.println(book);
  Class ob = book.getClass();
  Field titleField = ob.getDeclaredField(“title”);
  titleField.setAccessible(true);
  Method multiplePagesMethod = ob.getDeclaredMethod(“multiplePages”,int.class);
  multiplePagesMethod.setAccessible(true);
  titleField.set(book, “GoGoMango”);
  multiplePagesMethod.invoke(book,4);
  System.out.println(book);
 }
}

class Book
{
 private String title = “NoNameTitle”;
 private String author = “NoNameAuthor”;
 private int pages = 100;
 private void multiplePages(int num)
 {
  pages*=num;
 }
 public String toString()
 {
  return title+”:”+author+”:”+pages;
 }
}