Java中的字段 getBoolean() 方法及示例

Java.lang.reflect.Field类的getBoolean()方法用于获取类中包含的静态或实例布尔字段的值。当一个类包含一个静态或实例布尔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 boolean getBoolean(Object obj)
               throws IllegalArgumentException,
                      IllegalAccessException

参数：此方法接受单个参数obj ，它是从中提取布尔值的对象。

返回值：此方法返回所需的布尔字段的值。

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大转换转换为布尔类型，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 getBoolean() 方法：
方案一：

// 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;
    }
}

输出：

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

方案二：

// 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;
        }
    }
}

输出：

Value: false

参考资料： https: Java Java.lang.Object)