Java Class getDeclaredConstructors()用法及代碼示例

java.lang.Class類的getDeclaredConstructors()方法用於獲取此類的構造函數，這些構造函數是私有，公共，受保護或默認的構造函數。該方法以構造函數對象數組的形式返回此類的構造函數。

用法:

public Constructor[] getDeclaredConstructors()
                      throws SecurityException

參數：此方法不接受任何參數。

返回值：此方法以構造函數對象數組的形式返回此類的構造函數。

異常如果存在安全管理器且不滿足安全條件，則此方法將引發SecurityException。

下麵的程序演示了getDeclaredConstructors()方法。

示例1:

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

輸出：

Class represented by myClass: class Test
DeclaredConstructors of myClass: [public Test()]

示例2:

// Java program to demonstrate  
//getDeclaredConstructors() method 
  
import java.util.*; 
  
class Main { 
  
    public Object obj; 
  
    private Main() 
    { 
  
        class Arr { 
        }; 
  
        obj = new Arr(); 
    } 
  
    public static void main(String[] args) 
        throws ClassNotFoundException 
    { 
        // returns the Class object for this class 
        Class myClass = Class.forName("Main"); 
  
        System.out.println("Class represented by myClass: "
                           + myClass.toString()); 
  
        // Get the constructors of myClass 
        // using getDeclaredConstructors() method 
        System.out.println( 
            "DeclaredConstructors of myClass: "
            + Arrays.toString( 
                  myClass.getDeclaredConstructors())); 
    } 
}

輸出：

Class represented by myClass: class Main
DeclaredConstructors of myClass: [private Main()]

參考： https://docs.oracle.com/javase/9/docs/api/java/lang/Class.html#getDeclaredConstructors–

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