Java中的字段 setByte() 方法及示例

Java.lang.reflect.Field的setByte()方法用于将字段的值设置为指定对象上的字节。当您需要将对象字段的值设置为字节时，您可以使用此方法设置对象的值。

句法：

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

参数：此方法接受两个参数：

• obj ：这是应该修改其字段的对象，并且
• b ：这是被修改的 obj 字段的新值。

Return ：此方法不返回任何内容。

异常：此方法引发以下异常：

• IllegalAccessException：如果此 Field 对象正在强制执行Java语言访问控制并且基础字段是不可访问的或最终的。
• IllegalArgumentException：如果指定的对象不是声明基础字段（或其子类或实现者）的类或接口的实例，或者展开转换失败。
• NullPointerException：如果指定的对象为 null 并且该字段是实例字段。
• ExceptionInInitializerError：如果此方法引发的初始化失败。

下面的程序说明了 setByte() 方法：
方案一：

// 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;
}

输出：

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

方案二：

// 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;
}

输出：

Value after applying setByte is 20

参考： https: Java/lang/reflect/Field.html#setByte-java.lang.Object-byte-