How to change private variable in Java

Picture simple class

src/com/oop/Person.java

package com.oop;

public class Person {
    private String name;
    private String phone;

    public Person(String name, String phone) {
        this.name = name;
        this.phone = phone;
    }

    public String getName() {
        return name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
}

There are two private fields - name and phone. Name can be only set using constructor. We cannot modify the private variable in classic way. This can be done using reflection.

src/com/run/Run.java

package com.run;

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

public class Run {
    public static void main(String[] args) {
        try {
            Class c1 = Class.forName("com.oop.Person");
            Object p1 = c1.getConstructor(String.class, String.class).newInstance("John", "3242342");
            Method m1 = c1.getDeclaredMethod("getName");

            Object result = m1.invoke(p1);
            System.out.println(result);

            Field nameField = c1.getDeclaredField("name");
            nameField.setAccessible(true);
            nameField.set(p1,"Derrek");

            result = m1.invoke(p1);
            System.out.println(result);

        } catch (Exception e) {
            System.out.println("Exception: " + e.toString());
        }
    }
}

Using getDeclaredField instead getField let us access private and protected variables. Setting accessible flag allows us to modify it. Finally the output looks like:

John
Derrek