使用 Field 直接改變 object value

import java.lang.reflect.Field;

public class Main {

  public static void main(String[] args) throws Exception {
    MyClass o = new MyClass();
    Field field = MyClass.class.getDeclaredField("name");
    field.setAccessible(true);
    field.set(o, "Hello World");
    System.out.println(field.get(o));
  }

}

class MyClass {
  private String name;
}