Java Field getBoolean()用法及代碼示例

java.lang.reflect.Field類的getBoolean()方法用於獲取類中包含的靜態或實例布爾字段的值。當一個類包含一個靜態或實例布爾字段，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 boolean getBoolean(Object obj)
               throws IllegalArgumentException,
                      IllegalAccessException

參數：此方法接受單個參數obj，該對象是要從中提取布爾值的對象。

返回值：此方法返回必需的布爾字段的值。

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，或者如果不能通過擴展轉換將字段值轉換為布爾類型，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getBoolean()方法：
示例1:

// Java program to demonstrate the above 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 isEmployee field object 
        Field field = User.class.getField("isEmployee"); 
  
        // Apply getBoolean Method on User Object 
        // to get the value of isEmployee field 
        boolean value = field.getBoolean(user); 
  
        // print result 
        System.out.println("Value of Boolean Field"
                           + " isEmployee is " + value); 
  
        // Now Get the isActive field object 
        field = User.class.getField("isActive"); 
  
        // Apply getBoolean Method on User Object 
        // to get the value of isActive field 
        value = field.getBoolean(user); 
  
        // print result 
        System.out.println("Value of Boolean Field"
                           + " isActive is " + value); 
    } 
} 
  
// sample User class 
class User { 
  
    // static boolean values 
    public static boolean isEmployee = true; 
    public static boolean isActive = false; 
  
    public static boolean isEmployee() 
    { 
        return isEmployee; 
    } 
    public static void setEmployee(boolean isEmployee) 
    { 
        User.isEmployee = isEmployee; 
    } 
    public static boolean isActive() 
    { 
        return isActive; 
    } 
    public static void setActive(boolean isActive) 
    { 
        User.isActive = isActive; 
    } 
}

輸出：

Value of Boolean Field isEmployee is true
Value of Boolean Field isActive is false

示例2:

// Java program to demonstrate the above method 
  
import java.lang.reflect.Field; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws NoSuchFieldException, 
               SecurityException, 
               IllegalArgumentException, 
               IllegalAccessException 
    { 
  
        // Create the mathDigit class object 
        mathDigit math = new mathDigit(); 
  
        // Get the isEmployee field object 
        Field field = mathDigit.class.getField("isZero"); 
  
        // Apply getBoolean Method on field Object 
        // to get the value of isZero field 
        boolean value = field.getBoolean(math); 
  
        // print result 
        System.out.println("Value: " + value); 
    } 
  
    // mathDigit class 
    static class mathDigit { 
  
        public static boolean isZero = false; 
        public int number; 
  
        public static boolean isZero() 
        { 
            return isZero; 
        } 
        public static void setZero(boolean isZero) 
        { 
            mathDigit.isZero = isZero; 
        } 
        public int getNumber() 
        { 
            return number; 
        } 
        public void setNumber(int number) 
        { 
            this.number = number; 
        } 
    } 
}

輸出：

Value: false

參考文獻： https://docs.oracle.com/javase/10/docs/api/java/lang/reflect/Field.html#getBoolean(java.lang.Object)

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