Reflection in Java and Java reflection

Reflection in Java and Java reflection

Reflection, I have heard of it before, and I agree that if I want to write what kind of class is required, I will not be able to. Why should I explore other elements in human beings? So I have never learned anything about reflection, until a few days ago, you can see the quick slider image for modifying ListView, and you can see that reflection is needed.

I looked at reflection yesterday.

Concepts first

Reflection is a class that is known only when a runtime is loaded. It is informed of its complete structure and generates an object corpse, or sets or calls methods for its variables.

In other wordsUnderstanding classAndModify class

Understanding class is

Understanding the class from the constructor, member variables, methods, modifier of each element

Test class:

package test;public class MyObject {public int a ,b;public MyObject(){}public MyObject(int a, int b) {super();this.a = a;this.b = b;}public int sum(){return a+b;}public int minus(){return a-b;}public int multiply(){return a*b;}public int divide(){return a/b;}}

Class c = Class. forName ("test. MyObject ");

Slave Constructor

Constructor [] constructors = c. getConstructors (); for (int I = 0; I <constructors. length; I ++) {System. out. println ("------ method + I +" ----- >>> "+ constructors [I]. toString (); System. out. println ("-----> method name:" + constructors [I]. getName (); System. out. println ("-----> modifier:" + constructors [I]. getModifiers (); Class p [] = constructors [I]. getParameterTypes (); for (int j = 0; j <p. length; j ++) {System. out. println ("parameter j:" + p [j]) ;}}

Member variables

Field [] fields = c. getDeclaredFields (); for (int I = 0; I <fields. length; I ++) {Field f = fields [I]; System. out. println ("-------> variable name:" + f. getName (); System. out. println ("-------> variable type:" + f. getModifiers (); System. out. println ("-----> modifier:" + f. getType ());}

Method:

Method m [] = c. getDeclaredMethods (); for (int I = 0; I <m. length; I ++) {System. out. println ("------" + I + "method ----- >>>" + m [I]. toString (); System. out. println ("-----> method name:" + m [I]. getName (); System. out. println ("-----> modifier:" + m [I]. getModifiers (); System. out. println ("------> return value:" + m [I]. getReturnType (); Class p [] = m [I]. getParameterTypes (); for (int j = 0; j <p. length; j ++) {System. out. println ("parameter j:" + p [j]) ;}}

Understand the class from the above aspects

The following describes how to apply a class through reflection.

// Create the Class object Class [] p = new Class [2]; p [0] = int. class; p [1] = int. class; Constructor constructor = c. getConstructor (p); Object object = constructor. newInstance (34, 90); // modify the member variable Field fielda = c. getField ("a"); System. out. println ("-----> before change:" + fielda. get (object); fielda. setInt (object, 190); System. out. println ("-----> changed:" + fielda. get (object); // call the Method of the class Method method1 = c. getMethod ("sum"); Object sum = method1.invoke (object); System. out. println ("---> plus =" + sum );