Set private field value with reflection

Question

I have 2 classes: Father and Child

public class Father implements Serializable, JSONInterface {      private String a_field;      //setter and getter here  }  public class Child extends Father {     //empty class } 

With reflection I want to set a_field in Child class:

Class<?> clazz = Class.forName("Child"); Object cc = clazz.newInstance();  Field f1 = cc.getClass().getField("a_field"); f1.set(cc, "reflecting on life"); String str1 = (String) f1.get(cc.getClass()); System.out.println("field: " + str1); 

but I have an exception:

Exception in thread "main" java.lang.NoSuchFieldException: a_field

But if I try:

Child child = new Child(); child.setA_field("123"); 

it works.

Using setter method I have same problem:

method = cc.getClass().getMethod("setA_field"); method.invoke(cc, new Object[] { "aaaaaaaaaaaaaa" }); 

Answer 1

To access a private field you need to set Field::setAccessible to true. You can pull the field off the super class. This code works:

Class<?> clazz = Child.class; Object cc = clazz.newInstance();  Field f1 = cc.getClass().getSuperclass().getDeclaredField("a_field"); f1.setAccessible(true); f1.set(cc, "reflecting on life"); String str1 = (String) f1.get(cc); System.out.println("field: " + str1);