Java Field getDouble()用法及代码示例

java.lang.reflect.Field的getDouble()方法用于获取double值，该值必须为静态或实例字段类型。此方法还用于获取通过扩展转换可转换为double类型的另一个基本类型的值。当一个类包含一个静态或实例双精度字段并且我们想要获取该字段的值时，可以使用此方法返回Field的值。

用法:

public double getDouble(Object obj)
              throws IllegalArgumentException,
                     IllegalAccessException

参数：此方法接受单个参数obj，这是从中提取双精度值的对象。

返回值：此方法返回转换为double类型的字段的值。

异常：此方法引发以下异常：

IllegalAccessException：如果Field对象正在强制执行Java语言访问控制并且基础字段不可访问，则抛出此异常。
IllegalArgumentException：如果指定的对象不是声明基础字段的类或接口的实例，或者无法通过扩展转换将字段值转换为double类型，则抛出此异常。
NullPointerException ：如果指定对象为null并且该字段是实例字段，则抛出此异常。
ExceptionInInitializerError：如果此方法引发的初始化失败，则抛出此异常。

以下示例程序旨在说明getDouble()方法：
示例1:

// Java program to demonstrate the getDouble() 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 marks field object 
        Field field = User.class.getField("Marks"); 
  
        // Apply getDouble Method on User Object 
        // to get the value of Marks field 
        double value = field.getDouble(user); 
  
        // print result 
        System.out.println("Value of double Field"
                           + " Marks is " + value); 
  
        // Now Get the Fees field object 
        field = User.class.getField("Fees"); 
  
        // Apply getDouble Method on User Object 
        // to get the value of Fees field 
        value = field.getDouble(user); 
  
        // print result 
        System.out.println("Value of double Field"
                           + " Fees is " + value); 
    } 
} 
  
// sample User class 
class User { 
  
    // static double values 
    public static double Marks = 34.13; 
    public static double Fees = 3413.99; 
    public static String name = "Aman"; 
  
    public static double getMarks() 
    { 
        return Marks; 
    } 
  
    public static void setMarks(double marks) 
    { 
        Marks = marks; 
    } 
  
    public static double getFees() 
    { 
        return Fees; 
    } 
  
    public static void setFees(double fees) 
    { 
        Fees = fees; 
    } 
  
    public static String getName() 
    { 
        return name; 
    } 
  
    public static void setName(String name) 
    { 
        User.name = name; 
    } 
}

输出：

Value of double Field Marks is 34.13
Value of double Field Fees is 3413.99

示例2:

// Java program to demonstrate the getDouble() method 
  
import java.lang.reflect.Field; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws NoSuchFieldException, 
               SecurityException, 
               IllegalArgumentException, 
               IllegalAccessException 
    { 
  
        // Create the RealNumbers class object 
        RealNumbers real = new RealNumbers(); 
  
        // Get the value field object 
        Field field 
            = RealNumbers.class
                  .getField("value"); 
  
        // Apply getDouble Method on field Object 
        // to get the value of value field 
        double value = field.getDouble(real); 
  
        // print result 
        System.out.println("Value: " + value); 
    } 
  
    // RealNumbers class 
    static class RealNumbers { 
  
        // double field 
        public static double value 
            = 9999999.34567; 
  
        // getter and setter methods 
        public static double getValue() 
        { 
            return value; 
        } 
  
        public static void setValue(double value) 
        { 
            RealNumbers.value = value; 
        } 
    } 
}

输出：

Value: 9999999.34567

参考文献： https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Field.html#getDouble-java.lang.Object-

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注：本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 Field getDouble() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。