SourceMaking

import java.util.List;

import java.util.ArrayList;

 

abstract class Entity {

    protected static StringBuffer indent = new StringBuffer();

    public abstract void traverse();

}

 

class Product extends Entity {

    private int value;

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

    public void traverse() {

        System.out.println( indent.toString() + value );

}   }

 

class Box extends Entity {

    private List children = new ArrayList();

    private int  value;

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

    public void add( Entity c ) { children.add( c ); }

    public void traverse() {

        System.out.println( indent.toString() + value );

        indent.append( "   " );

        for (int i=0; i < children.size(); i++)

            ((Entity)children.get(i)).traverse();

        indent.setLength( indent.length() - 3 );

}   }

 

public class CompositeLevels {

    public static void main( String[] args ) {

        Box root = initialize();

        root.traverse();

    }

 

    private static Box initialize() {

        Box[] nodes = new Box[7];

        nodes[1] = new Box( 1 );

        int[] s = { 1, 4, 7 };

        for (int i=0; i < 3; i++) {

            nodes[2] = new Box( 21+i );

            nodes[1].add( nodes[2] );

            int lev = 3;

            for (int j=0; j < 4; j++) {

                nodes[lev-1].add( new Product( lev*10 + s[i] ) );

                nodes[lev] = new Box( lev*10 + s[i]+1 );

                nodes[lev-1].add( nodes[lev] );

                nodes[lev-1].add( new Product( lev*10 + s[i]+2 ) );

                lev++;

        }   }

        return nodes[1];

}   }