组成模式Composite

//Purpose.  Composite design pattern

//1. Create a "lowest common denominator" that makes classes interchangeable
//2. All concrete classes declare an "isa" relationship to the interface
//3. All "container" classes couple themselves to the interface
//4. "Container" classes use polymorphism as they delegate to their children

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
}  }