Java Field getByte()用法及代碼示例

java.lang.reflect.Field的getByte()方法用於獲取必須為靜態或實例字段類型的byte值。當一個類包含一個靜態或實例字節字段，而我們想獲取該字段的值時，則可以使用此方法返回Field的值。

用法:

public Byte getByte(Object obj)
            throws IllegalArgumentException,
                   IllegalAccessException

參數：此方法接受單個參數obj，它是要從中提取字節值的對象。

返回值：此方法返回轉換為字節類型的字段的值。

異常：此方法引發以下異常：

IllegalAccessException：如果Field對象正在強製執行Java語言訪問控製並且基礎字段不可訪問，則拋出此異常。
IllegalArgumentException：如果指定的對象不是聲明基礎字段的類或接口的實例，或者無法通過擴展轉換將字段值轉換為類型字節，則拋出此異常。
NullPointerException ：如果指定對象為null並且該字段是實例字段，則拋出此異常。
ExceptionInInitializerError：如果此方法引發的初始化失敗，則拋出此異常。

以下示例程序旨在說明getByte()方法：
示例1:

// 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; 
    } 
}

輸出：

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

示例2:

// 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; 
}

輸出：

Value: 12

參考文獻： https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Field.html#getByte-java.lang.Object-

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