Java | 反思地获取构造函数

Question

如果它的参数是,我如何反射性地得到构造函数Object ... objects.

我的构造函数:

  public MyClass ( Object ... objects )
  {
    if ( ! ( objects == null ) )
    {
      if ( objects.length > 0 && objects [ 0 ] instanceof Long )
      {
        setLatency ( ( Long ) objects [ 0 ] ) ;
      }
    }
  }

我现在怎么做到的:

Class< ? > clazz = Class.forName ( "MyClass" ) ;

Constructor< ? > clazzConstructor = clazz.getConstructor ( Object [ ].class ) ;

我尝试做什么:

Long latency = 1000L ;

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( latency ) ;

我得到java.lang.IllegalArgumentException:参数类型不匹配

如果latency == null,一切正常.

Answer 1

你的构造函数期望一个对象数组,但你传递一个对象数组Long.

包装latency到一个对象数组中会起作用,虽然要小心,因为newInstance()它本身期望Object ...,如果你只传递它Object[],它会将它解释为一个参数列表.所以你必须做这样的事情:

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( (Object)new Object[] { latency } ) ;

要么

MyClass myInstance = ( MyClass ) clazzConstructor.newInstance ( new Object[] { new Object[] { latency } } ) ;

第一个"愚弄"编译器将您的对象数组包装到另一个中,第二个明确地代替它.

(传递null仅起作用,因为null为null,无论参数的声明类型是什么.)

Answer 2

试试这种方式

MyClass myInstance = (MyClass) clazzConstructor
        .newInstance(new Object[] { new Object[] { latency } });

newInstance(Object ... initargs)需要对象数组作为参数.在构造函数中购买你的第一个参数也是对象数组,Object... o因此你需要在Object数组中再次包装它.

我用这个代码测试了它,似乎工作正常

class MyClass {
    private Long latency;

    public void setLatency(Long latency) {
        this.latency = latency;
    }
    public Long getLatency() {
        return latency;
    }

    public MyClass(Object... objects) {
        if (!(objects == null)) {
            if (objects.length > 0 && objects[0] instanceof Long) {
                setLatency((Long) objects[0]);
            }
        }
    }

    public static void main(String[] args) throws Exception {
        Class<?> clazz = MyClass.class;

        Constructor<?> clazzConstructor = clazz.getConstructor(Object[].class);
        System.out.println(clazzConstructor);

        Long latency = 1000L ;
        MyClass myInstance = (MyClass) clazzConstructor
                .newInstance(new Object[] { new Object[] { latency } });
        System.out.println(myInstance);
        System.out.println(myInstance.getLatency());
    }
}