Design pattern-python java Decorator mode

decorator Pattern Definition 　　　 The responsibility is dynamically attached to the object. To extend functionality, decorators provide a more resilient alternative than inheritance

Implementing a class Diagram

　　　　

features of decorator mode

A decorator and a decorated object have the same super-type . ( Note that this is the use of inheritance to achieve "type matching," rather than taking advantage of inheritance to get "behavior", behavior from decorators and base components, or a combination of relationships with other decorators )

B You can wrap an object with one or more adorners.

C because the decorator and the decorator have the same type, so any need for the original object of the occasion, can be replaced with decorative objects.

D decorators May, before and/or after the act entrusted to the decorator, add their own actions to achieve a specific purpose.

E objects can be decorated at any time, so you can decorate objects dynamically and without limits at runtime with your favorite decorators

decorator Pattern Implementation examples

Interface Widget {void Draw ();} 1. "Lowest common denominator" class TextField implements Widget {//3.   "Core" Class with "Isa" rel private int width, height;      Public TextField (int w, int h) {width = w;   Height = h;                                                } public void Draw () {System.out.println ("TextField:" + width + "," + height);}} 2.                           Second level base Classabstract class Decorator implements widgets {//with "Isa" relationship private Widget wid; 4.   "Hasa" Relationship public Decorator (Widget w) {wid = W;} public void Draw () {Wid.draw ();}//5. Delegation}class Borderdecorator extends Decorator {//6.   Optional Embellishment Public Borderdecorator (Widget W) {super (W);                                } public void Draw () {Super.draw (); 7.  Delegate to base class System.out.println ("Borderdecorator"); and add extRA stuff}}class Scrolldecorator extends Decorator {//6.   Optional Embellishment Public Scrolldecorator (Widget W) {super (W);                                } public void Draw () {Super.draw (); 7.  Delegate to base class System.out.println ("Scrolldecorator"); and add extra stuff}}//decorator can add his or her own behavior before or after the act of the delegate to achieve a specific purpose public class Decoratordemo {public static void Ma In (string[] args) {//8.                          Client have the responsibility to compose desired configurations Widget awidget = new Borderdecorator ( New Borderdecorator (New Scrolldecorator (New Textfie      LD (80, 24)));  Awidget.draw ();} }

The output is: textfield:80, 24
Scrolldecorator
Borderdecorator
Borderdecorator

A similar program that is implemented in contrast to the Python decoration pattern

def Bread (func):    def wrapper ():        print "</" "\>"        func ()        print "<\______/>"    Return Wrapperdef Ingredients (func):    def wrapper ():        print "#tomatoes #"        func ()        print "~salad~"    return wrapper@bread@ingredientsdef Sandwich (food= "--ham--"):    print foodif (__name__== "__main__"):    Sandwich ()

The JAVA I/O class uses the decorator pattern to implement many reading methods, and InputStream is the abstract component of the decorator. FilterInputStream is an abstract decorator, Linenumberinputstream is a concrete decorator, plus the ability to calculate the number of rows, Bufferinputstream is a plus buffered input function and ReadLine () The concrete decorator of the method

The following example is to write your own Java i./o adorner, converting all uppercase characters in the input stream into lowercase

Import Java.io.*;class Lowercaseinputstream extends Filterinputstream{public lowercaseinputstream (InputStream in) { Super (in);} Two read methods must be implemented one for byte array public int read () throws IOException {int c = super.read (); return (c = =-1? c:character.t Olowercase ((char) (c)));} public int read (byte[] b,int offset,int len) throws IOException {int result = Super.read (b, offset, len); for (int i =offset ; I < offset + result; i++) {B[i] = (byte) character.tolowercase ((char) b[i]);} return result;}} public class Inputtest {public static void main (string[] args) {int c;try{inputstream in = new Lowercaseinputstream (New Bu Fferedinputstream (New FileInputStream ("Test.txt")), while ((c = in.read ()) >= 0) {System.out.print ((char) c);} In.close ();} catch (IOException e) {e.printstacktrace ();}}

Design mode-python java Decorator mode