Field setByte() method in Java with Examples

setByte() method of java.lang.reflect.Field used to set the value of a field as a byte on the specified object. When you need to set the value of a field of an object as byte then you can use this method to set value over an Object. Syntax:

public void setByte(Object obj, byte b)
            throws IllegalArgumentException,
                   IllegalAccessException

Parameters: This method accepts  two parameters:

• obj: which is the object whose field should be modified and
• b: which is the new value for the field of obj being modified.

Return: This method returns nothing. Exception: This method throws the following Exception:

• IllegalAccessException: if this Field object is enforcing Java language access control and the underlying field is either inaccessible or final.
• IllegalArgumentException: if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementer thereof), or if an unwrapping conversion fails.
• NullPointerException: if the specified object is null and the field is an instance field.
• ExceptionInInitializerError: if the initialization provoked by this method fails.

Below programs illustrate setByte() method: Program 1:

Java

// Java program to illustrate setByte() method

import java.lang.reflect.Field;

public class GFG {

    public static void main(String[] args)
        throws Exception
    {

        // create user object
        Employee emp = new Employee();

        // print value of leaveLeft
        System.out.println(
            "Value of leaveLeft before "
            + "applying setByte is "
            + emp.leaveLeft);

        // Get the marks field object
        Field field
            = Employee.class
                  .getField("leaveLeft");

        // Apply setByte Method
        field.setByte(emp, (byte)2);

        // print value of leaveLeft
        System.out.println(
            "Value of leaveLeft after "
            + "applying setByte is "
            + emp.leaveLeft);

        // print value of age
        System.out.println(
            "Value of age before "
            + "applying setByte is "
            + emp.age);

        // Get the marks field object
        field = Employee.class.getField("age");

        // Apply setByte Method
        field.setByte(emp, (byte)56);

        // print value of age
        System.out.println(
            "Value of age after "
            + "applying setByte is "
            + emp.age);
    }
}

// sample class
class Employee {

    // static byte values
    public static byte age = 45;
    public static byte leaveLeft = 12;
}

Output:

Value of leaveLeft before applying setByte is 12
Value of leaveLeft after applying setByte is 2
Value of age before applying setByte is 45
Value of age after applying setByte is 56

Program 2:

Java

// Java program to illustrate setByte() method

import java.lang.reflect.Field;

public class GFG {

    public static void main(String[] args)
        throws Exception
    {

        // create user object
        User user = new User();

        // Get the id field object
        Field field = User.class
                          .getField("id");

        // Apply setByte Method
        field.setByte(user, (byte)20);

        // print value of isActive
        System.out.println(
            "Value after "
            + "applying setByte is "
            + user.id);
    }
}

// sample User class
class User {

    // static byte values
    public static byte id = 2;
}

Output:

Value after applying setByte is 20

Reference: https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Field.html#setByte-java.lang.Object-byte-