Java Notes: Reflection

First, the basic knowledge

Class is a generic superclass that encapsulates the state of a class or interface runtime. Class is the center of reflection in Java, where you can find information about a class at run time.

class Solution {    publicstaticvoidthrows  classnotfoundexception {         = String. class; // Get through class literals        c = "Hello World". GetClass (); // get        through GetClass c = Class.forName ("String"); // get        through forname false, solution. class . getClassLoader ());}    }

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Second, class reflection

ImportJava.lang.reflect.Modifier;Importjava.lang.reflect.TypeVariable;Importjava.util.List;classSolution { Public Static voidMain (string[] args) {Class C= List.class; intmodifier = 0;//modifier        if(C.isinterface ()) modifier= C.getmodifiers () &modifier.interfacemodifiers (); Elsemodifier = c.getmodifiers () &modifier.classmodifiers ();        System.out.println (modifier.tostring (Modifier)); Typevariable<?>[] types = C.gettypeparameters ();//Generic Parameters         for(typevariable t:types) System.out.println (T.gettypename ()); Class[] Interfaces= C.getinterfaces ();//implementing Interfaces         for(Class i:interfaces) System.out.println (i); }}

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Third, field reflection

field to get information about the fields in the class.

Import Java.lang.reflect.Field; class Solution {    publicstaticvoid  main (string[] args) {        Class< string> C = String. class ;         = c.getfields ();          for (Field field:fields)            System.out.println (field);         // Public static final Java.util.Comparator Java.lang.String.CASE_INSENSITIVE_ORDER     }}

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Iv. reflection of the method

Importjava.lang.reflect.*;classSolution {StaticString getmodifiers (executable exec) {intModifier =exec.getmodifiers (); if(execinstanceofMethod) modifier&=modifier.methodmodifiers (); Else if(execinstanceofConstructor) modifier&=modifier.constructormodifiers (); returnmodifier.tostring (Modifier); }    StaticString getparameters (executable exec) {parameter[] Parameters=exec.getparameters (); StringBuilder Str=NewStringBuilder ();  for(Parameter parameter:parameters) str.append (Parameter+ " "); returnstr.tostring (); }    StaticString getexceptions (executable exec) {StringBuilder str=NewStringBuilder (); Class[] CS=exec.getexceptiontypes ();  for(Class C:cs) str.append (c+ " "); returnstr.tostring (); }     Public Static voidMain (string[] args) {Class<Integer> C = Integer.class; Method[] Methods= C.getdeclaredmethods ();//do not include methods inherited from a superclass         for(Method method:methods) {System.out.println (Method.getname ());            System.out.println (GetModifiers (method));            System.out.println (GetParameters (method));        System.out.println (Getexceptions (method)); }    }}

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V. Reflection object Creation

No parameter constructor.

 class   MyClass {MyClass () {System.out.pri    Ntln ( "Constructor called"  class   solution { public  static  void   main (string[] args) {Class  <MyClass> c = Myclass.class  ;  try   {MyClass o  = c.newinstance ();        System.out.println (o);  catch  (instantiationexception |        Illegalaccessexception exc) {exc.printstacktrace (); }    }}

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With the parameter constructor.

ImportJava.lang.reflect.Constructor;classMyClass {MyClass (intI, String s) {System.out.println ("Constructor called");        System.out.println (i);    System.out.println (s); }}classSolution { Public Static voidMain (string[] args) {Class<MyClass> C = MyClass.class; Try{Constructor<MyClass> cons = C.getconstructor (int.class, String.class);//methods that can only call publicCons = C.getdeclaredconstructor (int.class, String.class);//all methods that can invoke this type of declarationMyClass o = cons.newinstance (0, "Hello World");        System.out.println (o); } Catch(Exception exc) {exc.printstacktrace (); }    }}

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The reflection call method.

ImportJava.lang.reflect.Method;classMyClass { Public Static voidprint (String s) {System.out.println (s); }}classSolution { Public Static voidMain (string[] args) {Class<MyClass> C = MyClass.class; Try{MyClass o=c.newinstance (); Method Method= C.getmethod ("Print", String.class); Method.invoke (O,"Hello World"); } Catch(Exception exc) {exc.printstacktrace (); }    }}

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Vi. Reflection Field Access

ImportJava.lang.reflect.Field;classMyClass { PublicString str = "Hello World";}classSolution { Public Static voidMain (string[] args) {Class<MyClass> C = MyClass.class; Try{MyClass o=c.newinstance (); Field name= C.getfield ("str"); String value=(String) name.get (o);            System.out.println (value); Name.set (O,"Hello World"); Value=(String) name.get (o);        System.out.println (value); } Catch(Exception exc) {exc.printstacktrace (); }    }}

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Access to non-accessible fields, methods, and constructors.

ImportJava.lang.reflect.Field;classMyClass {PrivateString str = "Hello World";}classSolution { Public Static voidMain (string[] args) {Class<MyClass> C = MyClass.class; Try{MyClass o=c.newinstance (); Field Str= C.getdeclaredfield ("str"); if(!str.isaccessible ()) str.setaccessible (true); String value=(String) str.get (o);        System.out.println (value); } Catch(Exception exc) {System.out.println (Exc.getmessage ()); }    }}

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Seven, array reflection

ImportJava.lang.reflect.Array;classSolution { Public Static voidMain (string[] args) {Try {            int[] ar = (int[]) Array.newinstance (int.class, 10);  for(inti = 0; I < 10; i++) array.set (AR, I, i);  for(inti = 0; I < 10; i++) System.out.println (Array.get (AR, i)); } Catch(Exception exc) {System.out.println (Exc.getmessage ()); }    }}

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Gets the array dimension.

ImportJava.lang.reflect.Array;classSolution { Public Static voidMain (string[] args) {Try {            int[] arr = (int[]) Array.newinstance (int.class, 5, 5); Class C=Arr.getclass (); inti = 0;  while(C.isarray ()) {C=C.getcomponenttype (); I++;        } System.out.println (i); } Catch(Exception exc) {System.out.println (Exc.getmessage ()); }    }}

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Expands an array.

ImportJava.lang.reflect.Array;Importjava.util.Arrays;classSolution {StaticObject Extend (object Oldarr) {intOldlength =array.getlength (Oldarr); intNewlength = Oldlength * 2; Class C=Oldarr.getclass (); Object NEWARR=array.newinstance (C.getcomponenttype (), newlength); System.arraycopy (Oldarr,0, NEWARR, 0, oldlength); returnNEWARR; }     Public Static voidMain (string[] args) {int[] arr =New int[5];  for(inti = 0; i < arr.length; i++) Arr[i]=i;        System.out.println (arrays.tostring (arr)); Arr= (int[]) extend (arr);  for(inti = 5; I < 10; i++) Arr[i]=i;    System.out.println (arrays.tostring (arr)); }}

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Java Notes: Reflection