If we would like to access Private Field and method using Reflection we just got to call setAccessible(true) on the sector or method object which you would like to access. Class.getDeclaredField(String fieldName) or Class.getDeclaredFields() are often wont to get private fields. Whereas Class.getDeclaredMethod(String methodName, Class<?>… parameterTypes) or Class.getDeclaredMethods() are often wont to get private methods.

Below program might not work on online IDEs like, compile and run the below program on offline IDEs only.

1. Accessing private Field

// Access Private Field Using Reflection in Java
import java.lang.reflect.Field;

// Student class declaration
class Student {

	// private fields
	private String name;
	private int age;

	// Constructor
	public Student(String name, int age)
	{
		this.name = name;
		this.age = age;
	}

	// Getters and setters
	public String getName() { return name; }

	public void setName(String name) { this.name = name; }

	private int getAge() { return age; }

	public void setAge(int age) { this.age = age; }

	// Override toString method to get required
	// output at terminal
	@Override public String toString()
	{
		return "Employee [name=" + name + ", age=" + age
			+ "]";
	}
}

// Program will throw an exception on online IDE
// Compile and run the program on offline IDE
class GFG {

	public static void main(String[] args)
	{
		try {

			// Student object created
			Student e = new Student("Kapil", 23);

			// Create Field object
			Field privateField
				= Student.class.getDeclaredField("name");

			// Set the accessibility as true
			privateField.setAccessible(true);

			// Store the value of private field in variable
			String name = (String)privateField.get(e);

			// Print the value
			System.out.println("Name of Student:" + name);
		}
		catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output:

Name of Student:Kapil

2. Accessing private Method

// Access Private Method Using Reflection in Java
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

// Student class declaration
class Student {

	// Private fields
	private String name;
	private int age;

	// Constructor
	public Student(String name, int age)
	{
		this.name = name;
		this.age = age;
	}

	// Getters and Setters
	public String getName() { return name; }

	public void setName(String name) { this.name = name; }

	private int getAge() { return age; }

	public void setAge(int age) { this.age = age; }

	// Override to string method to get
	// Required output when called
	@Override public String toString()
	{
		return "Employee [name=" + name + ", age=" + age
			+ "]";
	}
}

class GFG {

	public static void main(String[] args)
	{
		try {
			// Student class object
			Student e = new Student("Kapil", 23);

			// Create Method object
			Method privateMethod
				= Student.class.getDeclaredMethod("getAge");

			// Set the accessibility as true
			privateMethod.setAccessible(true);

			// Store the returned value of
			// private methods in variable
			int age = (int)privateMethod.invoke(e);
			System.out.println("Age of Student: " + age);
		}
		catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output:

Age of Student: 23