Java Reflection Field Access

We can get or set a field using reflection in two steps.

get the reference of the field.
To read the field's value, call the getXxx() method on the field, where Xxx is the data type of the field.
To set the value of a field, you call the corresponding setXxx() method.

Static and instance fields are accessed the same way.

Example

import java.lang.reflect.Field;
//fromwww.java2s.com
class MyClass {
 public String name = "Unknown";
 public MyClass() {
 }
 public String toString() {
 return "name=" + this.name;
 }
}
public class Main {
 public static void main(String[] args) {
 Class<MyClass> ppClass = MyClass.class;
 try {
 MyClass p = ppClass.newInstance();
 Field name = ppClass.getField("name");
 String nameValue = (String) name.get(p);
 System.out.println("Current name is " + nameValue);
 name.set(p, "abc");
 nameValue = (String) name.get(p);
 System.out.println("New name is " + nameValue);
 } catch (InstantiationException | IllegalAccessException
 | NoSuchFieldException | SecurityException | IllegalArgumentException e) {
 System.out.println(e.getMessage());
 }
 }
}

The code above generates the following result.

Bypassing Accessibility Check

To access non-accessible fields, methods, and constructors of a class using reflection call setAccessible(boolean flag) method from AccessibleObject class.

We need to call this method with a true argument to make that field, method, and constructor accessible.

import java.lang.reflect.Field;
//www.java2s.com
class MyClass {
 private String name = "Unknown";
 public MyClass() {
 }
 public String toString() {
 return "name=" + this.name;
 }
}
public class Main {
 public static void main(String[] args) {
 Class<MyClass> my = MyClass.class;
 try {
 MyClass p = my.newInstance();
 Field nameField = my.getDeclaredField("name");
 nameField.setAccessible(true);
 String nameValue = (String) nameField.get(p);
 System.out.println("Current name is " + nameValue);
 nameField.set(p, "abc");
 nameValue = (String) nameField.get(p);
 System.out.println("New name is " + nameValue);
 } catch (InstantiationException | IllegalAccessException
 | NoSuchFieldException | SecurityException | IllegalArgumentException e) {
 System.out.println(e.getMessage());
 }
 }
}

The code above generates the following result.