Question

java编程学习 求大神看看下面程序。“添加商品方法”是用构造方法写的，

在运行<添加商品>的功能的时候，为什么每次都是最新输入的商品信息会覆盖前面输入的商品信息？而我将构造方法改成用自定义方法，就不会出现这种情况呢？
程序：
import java.util.Scanner;
import java.util.ArrayList;
class Commodity{//商品类
private String commodityCode;//商品条码
private String commodityName;//商品名称
private double buyingPrice;//商品进价
private double sellingPrice;//商品卖价
private int inventorySum=0;//库存总数
public void setCommodityCode(String code){this.commodityCode=code;}
public String getCommodityCode(){return this.commodityCode;}
public void setCommodityName(String name){this.commodityName=name;}
public String getCommodityName(){return this.commodityName;}
public void setBuyingPrice(double price){this.buyingPrice=price;}
public double getBuyingPrice(){return buyingPrice;}
public void setSellingPrice(double price){this.sellingPrice=price;}
public double getSellingPrice(){return sellingPrice;}
public void setInventorySum(int sum){this.inventorySum=this.inventorySum+sum;}
public int getInventorySum(){return inventorySum;}
public String toString(){
String str="\t"+commodityCode+"\t"+commodityName+"\t"+inventorySum+"\t"+buyingPrice+"\t"+sellingPrice;
return str;
}
}
class SystemAction{//功能类
ArrayList <Commodity> arrList=new ArrayList <Commodity>();
//添加商品方法：
SystemAction(String code,String name,double buyingPrice,double sellingPrice,int shuliang){
Commodity goods=new Commodity();
goods.setCommodityCode(code);
goods.setCommodityName(name);
goods.setBuyingPrice(buyingPrice);
goods.setSellingPrice(sellingPrice);
goods.setInventorySum(shuliang);
arrList.add(goods);
System.out.println(arrList);
System.out.println(goods);
}
}
public class InventoryManagementSystem{//主程序类
public static void main(String args[]){
Scanner in=new Scanner(System.in);
System.out.println("------欢迎使用本系统！------");
boolean boo=true;
do{
System.out.println("请选择您要执行的操作：\n101：添加商品\n102：查询商品"+
"\n103：修改商品信息\n104：删除商品\n105：查看库存\n106：统计营业额\n107：统计利润"+
"\n108：退出系统");
int sel=in.nextInt();
switch(sel){
case 101:
System.out.println("请输入商品编码：");
String code=in.next();
System.out.println("请输入商品名称：");
String name=in.next();
System.out.println("请输入商品进价：");
double buyPrice=in.nextDouble();
System.out.println("请输入商品卖价：");
double sellPrice=in.nextDouble();
System.out.println("请输入商品进货数量：");
int shuliang=in.nextInt();
new SystemAction(code,name,buyPrice,sellPrice,shuliang);
break;
}
}while(boo);
}
}

若以下回答无法解决问题，邀请你更新回答

Answer 1

应该说，每次都new一个实例，就不会 。。。。。。。。。。。

追问

还是不明白╮(╯▽╰)╭