打印票据--java

import java.util.Random;
class commodity{ //商品
	private String type,size;
	public commodity(String s)    { type=s;}
	public String getType()       { return type; }
	public String getSize()       { return size; }
	public double price()         { return 0; }
	public void  addNumber(int n) { ;}
	public void deleteNumber()    { ;}
	public int getNumber()        { return 0;}
}
class Usb extends commodity{
	private double p=100; 
	private String size ="Inspire T10";
	public static int number;
	public void addNumber(int n)  { number+=n;}
	public void deleteNumber()    { number--;}
	public String getSize()       { return size; }
	public int getNumber()        { return number;}
	public Usb()                  { super("U盘"); }
	public double price()         { return p; }
	public String toString()      
	{ return getType()+"t"+getSize()+"t"+getNumber()+"t"+price()+"t"+price()*getNumber();   }
	public static Usb Create()    { return new Usb(); }
}
class Screen extends commodity{
	private double p=2000;
	private String size ="Inspire T11";
	public static int number;
	public void addNumber(int n)  { number+=n;}
	public void deleteNumber()    { number--;}
	public int getNumber()        { return number;}
	public String getSize()       { return size; }
	public Screen()               { super("显示器"); }
	public double price()         { return p; }
	public String toString()      
	{ return getType()+"t"+getSize()+"t"+getNumber()+"t"+price()+"t"+price()*getNumber();   }
	public static Screen Create() { return new Screen(); }
}
class Music extends commodity{
	private double p=300;
	private String size ="Inspire T12";
	public static int number;
	public void  addNumber(int n) { number+=n;}
	public void deleteNumber()    { number--;}
	public int getNumber()        { return number;}
	public String getSize()       { return size; }
	public Music()                { super("一对音箱"); }
	public double price()         { return p; }
	public String toString()      
	{ return getType()+"t"+getSize()+"t"+getNumber()+"t"+price()+"t"+price()*getNumber();   }
	public static Music Create()  { return new Music(); }
}
class shoppingCart{
	private commodity[] commodities;
	private int totalnum;//商品总数量
	private int cartlen=30; //购物车最大容量
	public shoppingCart () {
		commodities = new commodity[cartlen];
	}
	public void filtrate() {//过滤掉重复的
		commodity[] com=new commodity[cartlen];
		com[0]=commodities[0];
		int i,j,k; i=0;j=0;
		while(i cartlen)
		{
			System.out.print("购物车已满");
			return ;
		}
		for(int i=totalnum;i 
运行结果：