Reflection in Java

Three ways to get class classes and some methods

 PackageCn.lianxi.reflect;ImportJava.lang.reflect.Field;ImportJava.lang.reflect.Modifier;Importjava.util.Date; Public classStudent { PublicString name= "Small white"; Private intAge=24; protectedString sex= "Male"; intmoney=180; Static{System.out.println ("This is a static code block"); }     PublicStudent () {System.out.println ("This is a constructor"); }
}classa{ Public Static voidMain (String []args) {Try{System.out.println (); //three ways to get class classes//Student.class;            Class name. Classes; //new Student (). GetClass (); The name of the object. GetClass ();Class cla=class.forname ("cn.lianxi.reflect.Student");//Class.forName ("Full class name")SYSTEM.OUT.PRINTLN ("The package in which:" +cla.getpackage (). GetName ()); System.out.println ("Full class Name:" +cla.getname ()); System.out.println ("Abbreviated class Name:" +cla.getsimplename ()); //gets the access modifier for the class, with the return value int            intnum =cla.getmodifiers (); //The int type can be converted to the corresponding modifier by the ToString () of the modifierSystem.out.println (modifier.tostring (num)); } Catch(ClassNotFoundException e) {e.printstacktrace (); }    }}classb{ Public Static voidMain (String []args) {Try{Class CLA=class.forname ("Cn.lianxi.reflect.Student"); //field[] fields = C.getfields (); just get publicfield[] fields = Cla.getdeclaredfields ();//Get all             for(inti = 0; i < fields.length; i++) {System.out.println (fields[i]); }            //gets the access modifier for all properties of the default int value is 0 no corresponding string type             for(inti = 0; i < fields.length; i++) {System.out.println (modifier.tostring (Fields[i].getmodifiers ())); }        } Catch(ClassNotFoundException e) {e.printstacktrace (); }    }}

This is the result of the Mian method running in Class A

This is the package in which the static code block is located: Cn.lianxi.reflect class Name: cn.lianxi.reflect.Student abbreviation: studentpublic

This is the result of the Mian method running in class B

This is a static code block public java.lang.String cn.lianxi.reflect.Student.nameprivate int cn.lianxi.reflect.Student.ageprotected Java.lang.String Cn.lianxi.reflect.Student.sexint cn.lianxi.reflect.Student.moneypublicprivateprotected

Creating objects

class c{    publicstaticvoid  main (String []args) {        try  {             // Student stu = new Student (); coupling            Class C = class.forname ("cn.lianxi.reflect.Student");             // relative Coupling catch (   Exception e) {            e.printstacktrace ();}}    }         

Run results

This is a static code block, which is a constructor

　To open the private properties switch for a class

classd{ Public Static voidMain (String []args) {Try{Class C= Class.forName ("Cn.lianxi.reflect.Student"); Student Stu=(Student) c.newinstance (); Field field= C.getdeclaredfield ("Age"); //Open the switch to access private propertiesField.setaccessible (true);        System.out.println (Field.get (Stu)); } Catch(Exception e) {e.printstacktrace (); }    }}

Run results

This is a static code block, which is a constructor 24

　　

The private method that is added in the Student class/**     * Private method *     /Private    double getsum (double number) {        return number + ten;    }

　　Accessing Object Private Methods

classe{ Public Static voidMain (String []args) {Try{Class C= Class.forName ("Cn.lianxi.reflect.Student"); Student Stu=(Student) c.newinstance (); Method Method= C.getdeclaredmethod ("Getsum",Double.class); Method.setaccessible (true); //Execution Method            Doublesum = (Double) method.invoke (Stu, 50.0);        SYSTEM.OUT.PRINTLN (sum); } Catch(Exception e) {e.printstacktrace (); }    }}

Execution Result:

This is a static code block, which is a constructor 60.0

• Get the class of a particular class in one of the three ways Class , that is, the byte code for that class
• Class getConstructor(Class<?>... parameterTypes) gets constructed method object of the Call object
• Call is a method that constructs a method class Constructor newInstance(Object... initargs) new Object
• Classthe getMethod(String name, Class<?>... parameterTypes) Fetch method object for the calling object
• Call methods of the Method object class Method invoke(Object obj, Object... args) , call the corresponding method on the object

Reflection of an array

　

 PackageCn.lianxi.reflect;Importjava.util.Arrays; Public classArrayreflect { Public Static voidMain (string[] args) {int[] A1 =New int[]{1,2,3}; int[] A2 =New int[5]; int[] A3 =New int[2] [3]; System.out.println (A1.getclass ()= = A2.getclass ());//trueSystem.out.println (A1.getclass ());//class [ISystem.out.println (A3.getclass ());//class [[ISystem.out.println (A1.getclass (). Getsuperclass () = = A3.getclass (). Getsuperclass ());//trueSystem.out.println (A2.getclass (). Getsuperclass ());//class Java.lang.Object//The following sentence is not compiled: Error: (() Java: Non-comparable type: java.lang.class<capture#1, total? Extends int[]>
And Java.lang.class<capture#2, total? Extends Int[][]>//System.out.println (a1.getclass () = = A3.getclass ());Object []b3= A3;//through//The following sentence compilation does not pass Error: (+) Java: Incompatible type: int[] cannot be converted to java.lang.object[]//Object [] b1 = A1;String S1= "ABC"; System.out.println (arrays.aslist (A1));//[[[ Email protected]]System.out.println (Arrays.aslist (S1));//[ABC]    }}

Run results

true class [iclass [ itrueclass  java.lang.object[[[email PROTECTED]][ABC] 

Configuration file Loading

• class Loader loading read-only configuration files

Class name. Class.getclassloader (). getResourceAsStream (STR);

• The class name, Class.getresourceasstream (str), essentially invokes the class loader. Intercept as follows (Class.java under the Java.lang package)

 Public InputStream getResourceAsStream (String name) {    = resolvename (name);     = GetClassLoader0 ();     if (cl==null) {        //  A system class.        return Classloader.getsystemresourceasstream (name);    }     return Cl.getresourceasstream (name);}

About Path STR, the wording is a little fastidious.

• No slash, relative path:str = "config.properties";
• Slash, from the root path of the classpath:str = "/org/iot/ui/config.properties";

In the previous compilation of Java code, some conf/ folders to be added to the dependency or labeled as the source folder, which is clearly an XML file, no Java source code. From here, I now know that is the reason to load the configuration file using reflection

Introspection (introspector) & JavaBean

JavaBean the process of reading the value of attribute x: Capitalize, complement prefix, get method.

"X"--"X"--"GetX"--"methodgetx"

• Use your own introspection to manipulate

I don't use it at the moment, so I'm not going to put the code, only the core class

Simple implementation: Using java.beans.PropertyDescriptor classes

Troublesome implementation: Use the java.beans.Introspector class to traverse getBeanInfo The return value of the method

JavaBean must have a constructor with no parameters

• Using the Beanutils Toolkit

  • String and Integer conversions (Contrast (propertyutils)
  • Attribute Cascade Operations
  • Operation Map

Reflection in Java