Java中的类 getDeclaredField() 方法和示例

Java.lang.Class 类的getDeclaredField()方法用于获取该类的指定字段。该方法以Field对象的形式返回该类的指定字段。

句法：

public Field getDeclaredField(String fieldName)
       throws NoSuchMethodException,
              SecurityException

参数：此方法接受一个参数fieldName ，即要获取的字段。

返回值：该方法以Field对象的形式返回该类的指定字段。

异常此方法抛出：

• 如果未找到具有指定名称的字段，则NoSuchFieldException 。
• 如果名称为空，则出现NullPointerException
• 如果存在安全管理器并且不满足安全条件，则出现 SecurityException。

  下面的程序演示了 getDeclaredField() 方法。

  示例 1：

  // Java program to demonstrate
  // getDeclaredField() method
    
  import java.util.*;
    
  public class Test {
    
      public Object obj;
    
      public static void main(String[] args)
          throws ClassNotFoundException, NoSuchFieldException
      {
    
          // returns the Class object for this class
          Class myClass = Class.forName("Test");
    
          System.out.println("Class represented by myClass: "
                             + myClass.toString());
    
          String fieldName = "obj";
    
          // Get the field of myClass
          // using getDeclaredField() method
          System.out.println(
              fieldName + " Field of myClass: "
              + myClass.getDeclaredField(fieldName));
      }
  }
  

  输出：

  Class represented by myClass: class Test
  obj Field of myClass: public java.lang.Object Test.obj
  

  示例 2：

  // Java program to demonstrate
  // getDeclaredField() method
    
  import java.util.*;
    
  class Main {
    
      private Object obj;
    
      public static void main(String[] args)
          throws ClassNotFoundException, NoSuchFieldException
      {
    
          // returns the Class object for this class
          Class myClass = Class.forName("Main");
    
          System.out.println("Class represented by myClass: "
                             + myClass.toString());
    
          String fieldName = "obj";
    
          try {
              // Get the field of myClass
              // using getDeclaredField() method
              System.out.println(
                  fieldName + " Field of myClass: "
                  + myClass.getDeclaredField(fieldName));
          }
          catch (Exception e) {
              System.out.println(e);
          }
      }
  }
  

  输出：

  Class represented by myClass: class Main
  obj Field of myClass: private java.lang.Object Main.obj
  

  参考： https://docs.oracle.com/javase/9/docs/api/ Java/lang/Class.html#getDeclaredField-java.lang.String-