Java Class getDeclaredField()用法及代碼示例

java.lang.Class類的getDeclaredField()方法用於獲取此類的指定字段。該方法以Field對象的形式返回此類的指定字段。

用法:

public Field getDeclaredField(String fieldName)
       throws NoSuchMethodException,
              SecurityException

參數：此方法接受參數fieldName，這是要獲取的Field。

返回值：此方法以Field對象的形式返回此類的指定字段。

異常該方法拋出：

• NoSuchFieldException如果找不到具有指定名稱的字段。
• NullPointerException 如果名稱為null
• SecurityException如果存在安全管理員並且不滿足安全條件。

  下麵的程序演示了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)); 
      } 
  }

  輸出：

  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); 
          } 
      } 
  }

  輸出：

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

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