An example of using Java Reflection to invoke a private API method

PrivateMethodReflection.java

import java.lang.reflect.Method;
import java.util.Random;

public class PrivateMethodReflection {

	public static void main(String[] args) throws Exception {

		Person person = new Person("Bob");
		System.out.println("Name: " + person.getName());

		// call the private getID method get a reference to the Person class
		Class personClass = person.getClass();
		
		// get a reference to the private method
		Method getIDMethod = personClass.getDeclaredMethod("getID");
		
		// make the private method accessible 
		// (if you skip this step you get a IllegalAccessException)
		getIDMethod.setAccessible(true);
		// getID() method has no parameters so create an empty object 
		// array to pass for params
		Object[] noparams = new Object[] {};
		// invoke the getID method and cast the result to a Long return type
		// since the result is a long
		long id = (Long) getIDMethod.invoke((Object) person, noparams);

		System.out.println("ID: " + id);
	}

	public static class Person {
		private String name;
		private long id;

		public Person(String name) {
			this.name = name;

			Random rnd = new Random();
			id = rnd.nextLong();
		}

		public String getName() {
			return name;
		}

		// ///////// PRIVATE /////////////

		private long getID() {
			return id;
		}
	}

}