Java reflection is a matter of fact.

What is reflection

java reflection mechanism: The Java Reflection Mechanism is in the running state,

For any class, all the properties and methods of the class can be known;

For any object, it can call any of its methods and properties;

This dynamic acquisition of information and the ability to dynamically invoke the object's methods is called the reflection mechanism of the Java language.

Simply put: restore the full information of a class based on an object that has already been instantiated

modifying properties by Reflection

 PackageTest2016.demo;ImportJava.lang.reflect.Field; Public classDemo4 { Public Static voidMain (string[] args)throwsException {Student stu=NewStudent (); Field[] Fields=Stu.getclass (). Getdeclaredfields ();  for(Field f:fields) {f.setaccessible (true); //Set whether to allow access, not write run will error                          if(F.getname () = = "Name") {F.set (Stu,"Java"); } Else if(F.getname () = = "Age") {F.set (Stu,20);    }} System.out.println (Stu); //Output: java:20    }}classStudent {PrivateString name; Private intAge ;  PublicStudent () { This. Name = "Zhangsan";  This. Age = 10; }        //override the ToString method, otherwise output: [email protected]     PublicString toString () {return  This. Name + ":" + This. Age; }}

Calling methods by reflection

 PackageTest2016.demo;ImportJava.lang.reflect.Method; Public classDemo4 {@SuppressWarnings ("Unchecked")     Public Static voidMain (string[] args)throwsException {Student stu=NewStudent ("Zhangsan", 21); Class C=Stu.getclass (); //the GetMethod () method needs to pass in the method name and the parameter type of the method with the parametermethod = C.getmethod ("Score",int.class); //Invoke () indicates the meaning of the call and needs to pass in objects and parametersMethod.invoke (Stu, 100); Method m= C.getmethod ("Say", String.class); //the null representation is not called by the object, which is the static method, and the null transposition Stu is also possible.M.invoke (NULL, "Hello java!!!"); }}classStudent {PrivateString name; Private intAge ;  PublicStudent (String name,intAge ) {         This. Name =name;  This. Age =Age ; }         Public voidScore (intscore) {System.out.println ( This. Name + "Test" + score + "Score"); }         Public Static voidsay (String str) {System.out.println ("Just now I said:" +str); } @Override PublicString toString () {return  This. Name + "-" + This. Age; }}

Program output: Zhangsan a 100-point test.
I said just now: Hello java!!!

manipulating arrays by reflection

 PackageTest2016.demo;ImportJava.lang.reflect.Array; Public classDemo4 { Public Static voidMain (string[] args)throwsException {int[] arr = {1, 2, 3, 4, 5}; //Getcomponenttype () returns the class name of the data type of the data contained in your array. This is int .class<?> C =Arr.getclass (). Getcomponenttype (); System.out.println ("Array type:" + c.getname ());//array type: int                intLen =array.getlength (arr); System.out.println ("Array Length:" + len);//Array Length: 5System.out.print ("Traversing array:");  for(inti = 0; i < Len; i++) {System.out.print (Array.get (arr, i)+ " ");//traversing arrays: 1 2 3 4 5} System.out.println (); System.out.println ("Before modifying the third data:" + Array.get (arr, 2));//before you modify a third data: 3Array.set (arr, 2, 10); System.out.println ("Before modifying the third data:" + Array.get (arr, 2));//before modifying a third data:    }}

Note the point :

　　GetFields () differs from Getdeclaredfields ():

GetFields () can only access fields declared as public in a class, private fields that cannot be accessed, and access to public methods inherited from other classes.

Getdeclaredfields () can access all fields in a class, regardless of public,private,protect, and cannot access methods inherited from other classes

　　GetMethods () differs from Getdeclaredmethods ():

GetMethods () can only access methods declared as public in a class, private methods that it cannot access, and access to public methods inherited from other classes.

Getdeclaredfields () can access all fields in a class, regardless of public,private,protect, and cannot access methods inherited from other classes

GetConstructors () differs from getdeclaredconstructors ():

GetConstructors () can only access constructors declared as public in a class.

getdeclaredconstructors () can access all constructors in a class, regardless of Public,private,protect

　　　　

Java reflection is a matter of fact.