The Java Reflection class type is the class itself that can be manipulated how to get function parameters by reflection to return value function parameter __ block chain

Source: Internet
Author: User
Tags reflection

Personal understanding of Java Reflection: Reflection is a set of methods for understanding classes and using classes ;

The Java basics know how to instantiate a class, and also know how to invoke a variable or method through an instance;
But many times the class is not written by ourselves, so we do not know the class very well, and this time we can understand or invoke the class itself by reflection.
Let's say there's a class named A.

Class a{

To understand this class we can use it to create variables, call functions, but when you do not know the class, then about the function itself is not the start, how to do.
All classes are objects of class classes C1=a.class So what we come to is an equivalent to the class itself, such as C1, the official name is class type (class type), through C1 can do a series of operations on class A;

In depth, it is appropriate to have a class type called a bytecode file;
Because reflection exists only in the runtime , that is, at run time, the call has been compiledclass, such as Class C=a.class, can be understood as the call to a already compiled class file A.class, so all parameters related to reflection must be class type, corresponding to each compiled file, such as the use of reflection call annotations are Xx.class, and the life cycle of annotations must be runtime, so that these annotations exist at run time

0. Three types of reflection initialization

        Class C1=a.class;

        A a=new a ();
        Class C2=a.getclass ();

        try {
            Class c3=class.forname ("A");
        } catch (ClassNotFoundException e) {
            e.printstacktrace ();

1. Create an instance;


A a2= (a) c1.newinstance ();

The instance A2 of a is created, and the same instantiation function as Class A is implemented through class type C1
Then we get the surrogate C1 of Class A, so that we can do a series of operations on the class itself, such as the function inside the class, the return value of the function and the parameter value.

2. Methods

as follows, 3 functions are defined in Class A, and by C1.getmethod we get the
Method Set (method[] methods);
method returns the Value class type (class retype);
Method function value class type (class[] paratypes);
So that the function can be called further
Import java.lang.reflect.InvocationTargetException;
Import Java.lang.reflect.Method;

/** * Created by xuh-h on 2017/7/19. */public class SimpleTest {public static void main (string[] args) throws InvocationTargetException, Illegalaccessexc

        eption {Class c1=a.class;
            try {method M1=c1.getmethod ("Print", Int.class, Int.class);
            Method M2=c1.getmethod ("Print", New Class[]{string.class,string.class});
            M1.invoke (New A (), 1,2); Method[] Methods=c1.getdeclaredmethods (); function class type array for (methods Method:methods) {System.out.println ("method:" +

                Method.getname ());

                Class Retype = Method.getreturntype ();//function returns the value class type System.out.println ("Return:" +retype.getname ());
                        class[] Paratypes = Method.getparametertypes ();//function parameter class type array for (class Paratype:paratypes
                ) {System.out.println ("PARAMETER:" +paratype.getname ()); }

        } catch (Nosuchmethodexception e) {e.printstacktrace ();
    Class a{public void print (int a,int b) {System.out.println (a+b);
    public void print (String a,string b) {System.out.println (a.touppercase () + "" +b.tolowercase ());
    Public String print2 (int a,int b) {return "" +A*B; }

The result of the operation is to get the return value type and the parameter type of all functions in Class A, or to call the function in A;

   PARAMETER:java.lang.String method
: Print

So we see that when you do not know the class, or do not need to understand, just call can be easily achieved using reflection;

A class type is the class itself that can perform various operations

Another function is to implement dynamic loading,
Like what

Class.forName (Args[0])

The required classes can be loaded dynamically after compilation, at run time
Also like JDBC connection with MySQL,

Class.forName ("Driver")

The reflection is used

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.