Decorator Pattern

Wrap an object and extend the functionality of the wrapped object </ font>

In the sample code, instead of adding new functionality, I wrap the String object in parentheses.

Check with the following class structure

class	Explanation
abstract Display.class	Common type for each class Define abstract method
Message.class	Expand Display String field of this class is wrapped
Decorator.class	Expand Display Implement Decorator
user(Main.class)	Check the operation

User Includes the meaning that other developers use this pattern

Below is the sample code

`abstract_class_Display`


abstract class Display{
  abstract String getStr();
}

`Message.class`


class Message extends Display{
      String  msg;
      Message(String s){this.msg=s;}
      String  getStr() {return msg;} 
}

`Decorder.class`


class Decorator extends Display{
      Display   display;
      StringBuffer sb = new StringBuffer();
 
      Decorator(Display d){this.display=d;}
      String getStr(){
             return makeBorder(display.getStr());}
      String makeBorder(String msg){
             sb.append("<")
               .append(msg)
               .append(">");
             return sb.toString();
  }
}

`user(Main.class)`


public static void main(String[] args){
       Display d1 = new Message("Hello java");
       Display d2 = new Decorator(new Decorator(new Decorator(d1)));
       System.out.println(d2.getStr());
}