"Turn-and-organize" Java Reflection mechanism

Concept

It is the ability of a program to access, detect and modify its own state or behavior, and to adjust or modify the state and related semantics of the behavior described by the application according to the state and result of its behavior.

Reflection Mechanism effect

1, anti-compilation:. Class-->.java

2, through the reflection mechanism to access Java Object Properties, methods, construction methods, etc.;

Sun provides reflection mechanism classes

Java.lang.Class;

Java.lang.reflect.Constructor;

Java.lang.reflect.Field;

Java.lang.reflect.Method;

Java.lang.reflect.Modifier;

Reflection implementation

1. There are three ways of reflection realization

1 //The first way:2CLASSC1 = Class.forName ("Employee"); 3 //The second way:4 //each type in Java has a class attribute. 5CLASSC2 = Employee.class; 6    7 //The Third Way:8 //any Java object in the Java language has a GetClass method9Employeee =NewEmployee (); TenCLASSC3 = E.getclass ();//C3 is the runtime class (the run-time class for E is employee)

2. After getting the class, use Newinstance to create the object

1 Class C =class.forname ("Employee");   2   3 // Create a new instance  of the class represented by this class object 4 // an employee's parameterless construction method was called.  

3. Get Properties

① Get all Properties

　　

1 //get the entire class2Class C = class.forname ("Java.lang.Integer"); 3               //get all the properties? 4field[] fs =C.getdeclaredfields (); 5        6                    //defines a variable-length string used to store properties7StringBuffer SB =NewStringBuffer (); 8             //stitching each property into this string by appending the method9             //the outermost public definitionTenSb.append (Modifier.tostring (C.getmodifiers ()) + "class" + c.getsimplename () + "{\ n");  One             //each of the properties inside A              for(Field field:fs) { -Sb.append ("\ t");//Space -Sb.append (Modifier.tostring (Field.getmodifiers ()) + "");//gets the modifier for the property, such as Public,static, and so on theSb.append (Field.gettype (). Getsimplename () + "");//the name of the type of the property -Sb.append (Field.getname () + "; \ n");//Name of property + carriage return -             }   -        +Sb.append ("}");  -        +System.out.println (SB);

② get the specified property

　　

1  Public Static voidMain (string[] args)throwsexception{2               3<span style= "White-space:pre" > </span>//the previous way:4     /* 5 User U = new user ();6 u.age = n;//set7 System.out.println (u.age);//get8     */  9               Ten     //Get class OneClass C = class.forname ("User");  A     //Get ID Property -Field IdF = C.getdeclaredfield ("id");  -     //instantiate this class to assign O theObject o =c.newinstance ();  -     //Break Package -Idf.setaccessible (true);//using the reflection mechanism can break the encapsulation and cause the properties of the Java object to be unsafe.  -     //assigns the id attribute of the O object to "Max" +Idf.set (O, "110");//Set -     //Get + System.out.println (Idf.get (o));  A}

4, Get methods, and construction methods, no longer described in detail, just look at the keyword:

Method keyword	Meaning
Getdeclaredmethods()	Get all the methods
Getreturntype()	Get the return type of the method
Getparametertypes()	Get the incoming parameter type for a method
Getdeclaredmethod ("Method name", Parameter type. Class,......)	Get a specific approach
Constructor method keyword	Meaning
Getdeclaredconstructors()	Get all the construction methods
Getdeclaredconstructor (parameter type. Class,......)	Get a specific construction method
Parent class and Parent interface	Meaning
Getsuperclass()	Gets the parent class of a class
Getinterfaces()	Get an interface for a class implementation

"Turn-and-organize" Java Reflection mechanism