1 /**
   2  * DecoratorPattern example
   3  */
   4 
   5 abstract class Display {
   6     public abstract int getColumns();
   7     public abstract int getRows();
   8     public abstract String getRowText(int row);
   9     public final void show() {
  10         for(int i=0; i < getRows(); i++) {
  11             System.out.println(getRowText(i));
  12         }
  13     }
  14 }
  15 
  16 class StringDisplay extends Display {
  17     private String string;
  18     public StringDisplay(String string) {
  19         this.string = string;
  20     }
  21     public int getColumns() {
  22         return string.getBytes().length;
  23     }
  24     public int getRows() {
  25         return 1;
  26     }
  27     public String getRowText(int row) {
  28         if(row == 0) {
  29             return string;
  30         } else {
  31             return null;
  32         }
  33     }
  34 }
  35 
  36 abstract class Border extends Display {
  37     protected Display display;
  38     protected Border(Display display) {
  39         this.display = display;
  40     }
  41 }
  42 
  43 class SideBorder extends Border {
  44     private char borderChar;
  45     public SideBorder(Display display, char ch) {
  46         super(display);
  47         this.borderChar = ch;
  48     }
  49     public int getColumns() {
  50         return 1 + display.getColumns() + 1;
  51     }
  52     public int getRows() {
  53         return display.getRows();
  54     }
  55     public String getRowText(int row) {
  56         return borderChar + display.getRowText(row) + borderChar;
  57     }
  58 }
  59 
  60 class FullBorder extends Border {
  61     public FullBorder(Display display) {
  62         super(display);
  63     }
  64     public int getColumns() {
  65         return 1 + display.getColumns() + 1;
  66     }
  67     public int getRows() {
  68         return 1 + display.getRows() + 1;
  69     }
  70     public String getRowText(int row) {
  71         if(row == 0) {
  72             return "+" + makeLine('-', display.getColumns()) + "+";
  73         } else if(row == display.getRows()+1) {
  74             return "+" + makeLine('-', display.getColumns()) + "+";
  75         } else {
  76             return "|" + display.getRowText(row-1) + "|";
  77         }
  78     }
  79     private String makeLine(char ch, int count) {
  80         StringBuffer buf = new StringBuffer();
  81         for(int i=0; i < count; i++) {
  82             buf.append(ch);
  83         }
  84         return buf.toString();
  85     }
  86 }
  87 
  88 public class DecoratorDisplay {
  89     public static void main(String[] args) {
  90         Display b1 = new StringDisplay("Hello, world.");
  91         Display b2 = new SideBorder(b1, '#');
  92         Display b3 = new FullBorder(b2);
  93         b1.show();
  94         b2.show();
  95         b3.show();
  96 
  97         Display b4 = new SideBorder(
  98                 new FullBorder(
  99                     new FullBorder(
 100                         new SideBorder(
 101                             new FullBorder(b1), '*'
 102                             )
 103                         )
 104                     ), '/'
 105                 );
 106         b4.show();
 107     }
 108 }