java playground

MyClass.java

import java.lang.reflect.*;

class MyClass {

    private String privateField = "privateValue";

    public MyClass() {}

    public MyClass(String arg) {
        this.privateField = arg;
    }

    private void privateMethod(String arg) {
        System.out.println("Private Method called with arg: " + arg);
    }

    public String getPrivateField() {
        return privateField;
    }

}

ReflectionExample.java

import java.lang.reflect.*;

public class ReflectionExample {
    public static void main(String[] args) throws Exception {
        Class<?> clazz = MyClass.class;

        // Access private field
        Field field = clazz.getDeclaredField("privateField");
        field.setAccessible(true);
        MyClass obj = new MyClass();
        System.out.println("Initial Field Value: " + field.get(obj));

        field.set(obj, "newPrivateValue");
        System.out.println("Updated Field Value: " + field.get(obj));

        // Access private method
        Method method = clazz.getDeclaredMethod("privateMethod", String.class);
        method.setAccessible(true);
        method.invoke(obj, "testArg");

        // Access private contructor
        Constructor<?> constructor = clazz.getDeclaredConstructor(String.class);
        constructor.setAccessible(true);
        MyClass newObj = (MyClass) constructor.newInstance("newInstanceArg");
        System.out.println("New Object Field Value: " + newObj.getPrivateField());
     }
}