Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

Calling Private Methods Publicly?

DZone's Guide to

Calling Private Methods Publicly?

· Java Zone ·
Free Resource

Verify, standardize, and correct the Big 4 + more– name, email, phone and global addresses – try our Data Quality APIs now at Melissa Developer Portal!

We Java developers, known 4 access modifiers in Java: private, protected, public, and package. Well, except for the private, the last three, can be called from outside of the class by inheritance, same package or from the instance.

Now, the common question, can private be called publicly (from outside class)? well the answer is NO and YES. No when you use ‘usual’ way to access it, and YES when you ‘hack’ into it using the Reflection API provided by Java itself.

Well okay, now just write the code that we will hack into. I called it as “TheVictim

package com.namex.hack;

public class TheVictim {
	private void hackTest() {
		System.out.println("hackTest called");
	}

	private static void hackTestStatic() {
		System.out.println("hackTestStatic called");
	}

}

Now after that, just follow my code and try to run it. I guarantee that if you followed it right, you will get TheVictim to call both of the hackTest and hackTestStatic. And you can see the output on your screen.

package com.namex.hack;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

public class HackTest {
	public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {

		Class c = TheVictim.class;

		Method[] ms = c.getDeclaredMethods();

		for (Method each : ms) {
			String methodName = each.getName();
			each.setAccessible(true); // this is the key
			if (Modifier.isPrivate(each.getModifiers())) {
				
				if (Modifier.isStatic(each.getModifiers())) {
					// static doesnt require the instance to call it.
					each.invoke(TheVictim.class, new Object[] {});
				} else {
					each.invoke(new TheVictim(), new Object[] {});
				}
			}
		}

	}
}


Output example:

hackTestStatic called
hackTest called

Okay, this tutorial has met its purpose. Now you know the Reflection API of java is very powerful feature of programming language. And it’s all up to you to modify or even extend it for your own purpose. Have fun with Java :)

 

 

 

Developers! Quickly and easily gain access to the tools and information you need! Explore, test and combine our data quality APIs at Melissa Developer Portal – home to tools that save time and boost revenue. 

Topics:

Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}