Java Class getDeclaredField()用法及代码示例

java.lang.Class类的getDeclaredField()方法用于获取此类的指定字段。该方法以Field对象的形式返回此类的指定字段。

用法:

public Field getDeclaredField(String fieldName)
       throws NoSuchMethodException,
              SecurityException

参数：此方法接受参数fieldName，这是要获取的Field。

返回值：此方法以Field对象的形式返回此类的指定字段。

异常该方法抛出：

• NoSuchFieldException如果找不到具有指定名称的字段。
• NullPointerException 如果名称为null
• SecurityException如果存在安全管理员并且不满足安全条件。

  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-