Java中的字段 getByte() 方法及示例

Java.lang.reflect.Field的getByte()方法用于获取字节的值，该值必须是静态或实例字段类型。当一个类包含一个静态或实例字节字段并且我们想要获取该字段的值时，我们可以使用此方法返回字段的值。

句法：

public Byte getByte(Object obj)
            throws IllegalArgumentException,
                   IllegalAccessException

参数：此方法接受单个参数obj ，它是从中提取字节值的对象。

返回值：该方法返回字段转换为字节类型的值。

异常：此方法抛出以下异常：

1. IllegalAccessException：如果 Field 对象正在执行Java语言访问控制并且基础字段不可访问，则会引发此异常。
2. IllegalArgumentException：如果指定的对象不是声明基础字段的类或接口的实例，或者如果字段值无法通过扩展转换转换为类型字节，则会引发此异常。
3. NullPointerException：如果指定对象为空且字段为实例字段，则抛出此异常。
4. ExceptionInInitializerError：如果此方法引发的初始化失败，则抛出此异常。

下面的程序说明了 getByte() 方法：
方案一：

// Java program to demonstrate the getByte() method
  
import java.lang.reflect.Field;
  
public class GFG {
  
    public static void main(String[] args)
        throws NoSuchFieldException,
               SecurityException,
               IllegalArgumentException,
               IllegalAccessException
    {
  
        // Create the User class object
        User user = new User();
  
        // Get the identificationByte field object
        Field field
            = User.class
                  .getField("identificationByte");
  
        // Apply getByte Method on User Object
        // to get the value of identificationByte field
        byte value = field.getByte(user);
  
        // print result
        System.out.println("Value of Byte Field"
                           + " identificationByte is "
                           + value);
  
        // Now Get the selectionByte field object
        field = User.class.getField("selectionByte");
  
        // Apply getByte Method on User Object
        // to get the value of selectionByte field
        value = field.getByte(user);
  
        // print result
        System.out.println("Value of Byte Field"
                           + " selectionByte is "
                           + value);
    }
}
  
// sample User class
class User {
  
    // static Byte values
    public static byte identificationByte = 'E';
    public static byte selectionByte = 121;
  
    // getter and setter methods
    public static byte getIdentificationByte()
    {
        return identificationByte;
    }
  
    public static void
    setIdentificationByte(byte identificationByte)
    {
        User.identificationByte = identificationByte;
    }
  
    public static byte getSelectionByte()
    {
        return selectionByte;
    }
    public static void
    setSelectionByte(byte selectionByte)
    {
        User.selectionByte = selectionByte;
    }
}

输出：

Value of Byte Field identificationByte is 69
Value of Byte Field selectionByte is 121

方案二：

// Java program to demonstrate the getByte() method
  
import java.lang.reflect.Field;
  
import java.lang.reflect.Field;
  
public class GFG {
  
    public static void main(String[] args)
        throws NoSuchFieldException,
               SecurityException,
               IllegalArgumentException,
               IllegalAccessException
    {
  
        // Create the Codes class object
        Codes codes = new Codes();
  
        // Get the value field object
        Field field
            = Codes.class.getField("value");
  
        // Apply getByte Method on field Object
        // to get the value of value field
        byte value = field.getByte(codes);
  
        // print result
        System.out.println("Value: " + value);
    }
}
// Codes class
class Codes {
    // Byte field
    public static byte value = 12;
}

输出：

Value: 12

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