Composite in Java

interface Component { void traverse(); }      // 1. "lowest common denominator" 

 

class Primitive implements Component {        // 2. "Isa" relationship

   private int value;

   public Primitive( int val ) { value = val; }

   public void traverse()      { System.out.print( value + "  " ); }

}

 

abstract class Composite implements Component {      // 2. "Isa" relationship

   private Component[] children = new Component[9];  // 3. Couple to interface

   private int         total    = 0;

   private int         value;

   public Composite( int val )    { value = val; }

   public void add( Component c ) { children[total++] = c; } // 3. Couple to

   public void traverse() {                                  //    interface

      System.out.print( value + "  " );

      for (int i=0; i < total; i++)

          children[i].traverse();            // 4. Delegation and polymorphism 

}  }

 

class Row extends Composite {                // Two different kinds of "con-

   public Row( int val ) { super( val ); }   // tainer" classes.  Most of the

   public void traverse() {                  // "meat" is in the Composite

      System.out.print( "Row" );             // base class.

      super.traverse();

}  }

 

class Column extends Composite {

   public Column( int val ) { super( val ); }

   public void traverse() {

      System.out.print( "Col" );

      super.traverse();

}  }

 

public class CompositeDemo {

   public static void main( String[] args ) {

      Composite first  = new Row( 1 );          // Row1

      Composite second = new Column( 2 );       //   |

      Composite third  = new Column( 3 );       //   +-- Col2

      Composite fourth = new Row( 4 );          //   |     |

      Composite fifth  = new Row( 5 );          //   |     +-- 7

      first.add( second );                      //   +-- Col3

      first.add( third  );                      //   |     |

      third.add( fourth );                      //   |     +-- Row4

      third.add( fifth  );                      //   |     |     |

      first.add(  new Primitive( 6 ) );         //   |     |     +-- 9

      second.add( new Primitive( 7 ) );         //   |     +-- Row5

      third.add(  new Primitive( 8 ) );         //   |     |     |

      fourth.add( new Primitive( 9 ) );         //   |     |     +-- 10

      fifth.add(  new Primitive(10 ) );         //   |     +-- 8

      first.traverse();                         //   +-- 6

}  }