Java Basic Learning Note "12" Reflect reflex (2)

1. using reflection to create objects
   (1) public T newinstance (): You can only create objects that are not private, no parameter constructs, like the new Class ()

   12	Class<Teacher> clz = Teacher.class; Teacher t2 = clz.newInstance();

   (2) first get a constructor, call a method in the constructor, T newinstance (Object ... initargs), Initargs represents the constructor's required actual parameters

   123	Constructor<Teacher> con = clz.getDeclaredConstructor(String.class);con.setAccessible(true);//假如访问的是私有的就要把setAccsessable设置为true，因为是有成员不能直接访问Teacher t = con.newInstance("will");

   Before accessing a private member: set it to be accessible, AccessibleObject: Represents the accessible object, is the parent of the contructor,method,filed;
   method: Void Setaccessible (Boolean flag): used to set whether accessible, to set accessible: Obj.setaccessible (true);
2. Reflection Access executes the obtained method:

   123456

   Class<InvokeMethodByVarArgsDemo> clz =InvokeMethodByVarArgsDemo.class;Method m = clz.getMethod("show", int[].class);//调用public static void show(int ...is)m.invoke(null,new int[]{1,2,3});//YES                            //m.invoke(null,1,2,3);//ERRORm.invoke(null,(Object)new int[]{1,2,3});//YESm.invoke(null,new Object[]{new int[]{1,2,3}});//YES   访问静态方法不需要实例所以第一个参数可以为null

   public object Invoke (Object obj,object . args)    new object[]{pass the actual parameters}; General practice; TD class= "Code" >

   1

4. 12 public static <t extends Number> list<t> aslist (T ... a) { } method m = Clz.getmethod ( class
6. (2) return: Use the parameter args to assign the result of the method represented by the object on obj  
8. 123 object ret= new object[]{ 1 2 3 } array.getlength (ret) //gets the length of the array array.get (ret, i) //gets the value of the first I in the array ret
9. use reflection to get the field and set the value:

   1234	Class<Cat> clz = Cat.class;//使用反射得到Car类了的字段,并赋值,和取值 Field[] fs = clz.getDeclaredFields(); Field f = clz.getDeclaredField("name");  f.getName() //取出字段的值

   set the value of the field:

   1	voidset(Object obj, Object value)

   Sets the field that is represented by this field object on the specified object variable to the specified new value.
   parameter: Obj-the object to which the underlying field belongs (instance object) value-The new value of the field of the obj being modified

   123	cat C = clz.newinstance ();   F.setaccessible ( true );  //first set to access f.set (c, "Lucy" ); //setting instance C fields The value of name is Lucy

11. tbody> 12345 class<?> GetType () //returns a class object that identifies the claim type of the field represented by this Field object. type Getgenerictype () //returns a Type object that represents this Field The Declaration type of the field that the object represents. parameterizedtype is a type subclass that represents a parameterized type, that is, a generic type type[] Getactualtypearguments () //returns an array of type objects that represent the actual type parameters of this type. type Getrawtype () //returns a type object that represents a class or interface that declares this type.

12. 123	Type t = this.getClass().getGenericSuperclass(); ParameterizedType pt = (ParameterizedType) t; clz = (Class<T>) pt.getActualTypeArguments()[0]; //获取的是数组，强转为指定的类型

    An instance of this represented in the constructor of a generic parent class when the subclasses of the class are instantiated in a generic type .
    return value return clz.newinstance (); represents an instance of T
    
    
    
    

Java Basic Learning Note "12" Reflect reflex (2)