老师，我写好代码后点击运行，一点反应都没有，我实在查不出来哪有问题，老师帮我看看

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//商品类
package com.shopping.management;
//商品类
public class Goods {
//属性
    private String goodsId;
    private String goodsName;
    private double price;
    private String goodsDesp;
    //构造方法
    public Goods(String goodsId, String goodsName, double price, String goodsDesp) {
        super();
        this.goodsId = goodsId;
        this.goodsName = goodsName;
        this.price = price;
        this.goodsDesp = goodsDesp;
    }
    public String getGoodsId() {
        return goodsId;
    }
    public void setGoodsId(String goodsId) {
        this.goodsId = goodsId;
    }
    public String getGoodsName() {
        return goodsName;
    }
    public void setGoodsName(String goodsName) {
        this.goodsName = goodsName;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    public String getGoodsDesp() {
        return goodsDesp;
    }
    public void setGoodsDesp(String goodsDesp) {
        this.goodsDesp = goodsDesp;
    }
    //重写toString方法
    @Override
    public String toString() {
        return "编号：" + goodsId + ", 名称：" + goodsName + ", 价格：" + price + ", 描述："
                + goodsDesp + "]";
    }
    @Override
    //重写hashCode方法
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((goodsDesp == null) ? 0 : goodsDesp.hashCode());
        result = prime * result + ((goodsId == null) ? 0 : goodsId.hashCode());
        result = prime * result + ((goodsName == null) ? 0 : goodsName.hashCode());
        long temp;
        temp = Double.doubleToLongBits(price);
        result = prime * result + (int) (temp ^ (temp >>> 32));
        return result;
    }
    //重写equals方法
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj.getClass()==Goods.class) {
         Goods goods = (Goods)obj;
        return (goods.getGoodsDesp()).equals(goodsDesp)&&(goods.getGoodsId()).equals(goodsId)&&(goods.getGoodsName()).equals(goodsName)&&goods.getPrice()==price;
    }
        return false;
    }
}
 
 
//商品管理类
package com.shopping.management;
//商品管理类
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
 
public class GoodsManage {
    //存放商品的容器
     
private Set goodsSet;
//实例化商品对象
Goods one=new Goods("goods004","手机",2300.0,"android手机");
Goods two=new Goods("goods002","饮水机",299.0,"带净化功能的饮水机");
Goods three=new Goods("goods003","笔记本电脑",4999.0,"15寸笔记本电脑");
Goods four=new Goods("goods001","水杯",56.0,"不锈钢水杯");
public GoodsManage() {
     
}
public GoodsManage(Set goodsSet) {
    super();
    this.goodsSet = goodsSet;
}
 
public Set getGoodsSet() {
    return goodsSet;
}
 
public void setGoodsSet(Set goodsSet) {
    this.goodsSet = goodsSet;
}
//导入商品信息
public void importGoods() {
    goodsSet=new HashSet();
    goodsSet.add(one);
    goodsSet.add(two);
    goodsSet.add(three);
    goodsSet.add(four);
}
//显示商品信息
public void displayAllGoods() {
    Iterator it=goodsSet.iterator();
    while(it.hasNext()) {
        System.out.println("所有商品的信息为：");
        System.out.println(it.next());
    }
}
}
 
 
 
//购物车中商品信息类
package com.shopping.management;
//购物车中商品信息类
public class GoodsInCart {
//属性
private Goods goods;
private int num;
//构造方法
public GoodsInCart(Goods goods, int num) {
    super();
    this.goods = goods;
    this.num = num;
}
public Goods getGoods() {  
    return goods;
}
public void setGoods(Goods goods) {
    this.goods = goods;
}
public int getNum() {
    return num;
}
public void setNum(int num) {
    this.num = num;
}
 
}
 
 
//购物车类
package com.shopping.management;
//购物车类
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.Set;
 
public class ShoppingCart {
    //购物车属性，String类型的key，和GoodsInCart类型的value
private Map <String,GoodsInCart>shoppingCart=new HashMap<String,GoodsInCart>();
//构造方法
public ShoppingCart() {
     
}
public ShoppingCart(Map<String, GoodsInCart> shoppingCart) {
    super();
    this.shoppingCart = shoppingCart;
}
 
public Map<String, GoodsInCart> getShoppingCart() {
    return shoppingCart;
}
 
public void setShoppingCart(Map<String, GoodsInCart> shoppingCart) {
    this.shoppingCart = shoppingCart;
}
//添加商品到购物车方法
public void addGoodsToCart(GoodsManage gm) {
    Set <Goods> set=gm.getGoodsSet();
    Scanner sc=new Scanner(System.in);
    String str=null;
    Goods goods=null;
    boolean flag=false;
    if(set.size()==0) {
        System.out.println("请先导入商品信息！");
    }
    else {
        gm.displayAllGoods();
        System.out.println("请输入要添加的商品编号：");
        str=sc.next();
        for(Goods good:set) {
            if(good.getGoodsId().equals(str)) {
                flag=true;
                goods=good;
                break;
            }   
        }
        if(flag=true) {
            System.out.println("请输入要添加商品的数量：");
            int num=sc.nextInt();
            GoodsInCart goodsInCart=new GoodsInCart(goods,num);
            shoppingCart.put(str, goodsInCart);
        }
    }
}
//修改购物车中的商品数量方法
public void updateNumInCart() {
    System.out.println("请输入要修改的商品编号：");
    Scanner sc=new Scanner(System.in);
    Set<String>keySet=shoppingCart.keySet();
    int n=0;
    for(String key:keySet) {
        if(key.equals(sc.next())) {
            System.out.println("请输入要修改的商品数量：");
            n=sc.nextInt();
            if(n==0) {
                keySet.remove(key);
                System.out.println("因为该商品数量为零，所以该商品已移除！");
            }
            else {
                shoppingCart.get(key).setNum(n);
            }
        }
    }
}
//显示购物车中的所有商品方法
public void displayAllInCart() {
    Set<Entry<String,GoodsInCart>> entrySet=shoppingCart.entrySet();
    if(entrySet.size()==0) {
        System.out.println("您还未添加任何商品，快去挑选吧！");
    }
    else {
        for(Entry<String,GoodsInCart>entry:entrySet) {
            System.out.println(entry.getKey()+entry.getValue()+"个");
        }
    }
}
//结算方法
public void settleAccounts() {
    double allPrice=0;
    Set<Entry<String,GoodsInCart>> entrySet=shoppingCart.entrySet();
    for(Entry<String,GoodsInCart>entry:entrySet) {
        allPrice+=((entry.getValue().getNum())*(entry.getValue().getGoods().getPrice()));
    }
    System.out.println("商品的总价为："+allPrice);
    for(Entry<String,GoodsInCart>entry:entrySet) {
        System.out.println(entry.getKey()+entry.getValue()+"个");
}
}
//属性：
//
//－ 购物车（shoppingCart）:Map类型，其中key为String类型，value为GoodsInCart类型
//
//方法：
//
//－添加商品到购物车：
//
//   public void addGoodsToCart(GoodsManage gm);
//
//－修改购物车中的商品数量：public void updateNumInCart();
//
// - 显示购物车中的所有商品：public void displayAllInCart();
//
// - 结算：public void settleAccounts();
//
// - 构造方法及getter和setter方法
}
 
 
//测试类
package com.shopping.management;
 
import java.util.InputMismatchException;
import java.util.Scanner;
 
public class TestDemo {
    public void menu() {
        System.out.println("**********************************");
        System.out.println("***主菜单***");
        System.out.println("1--商品管理");
        System.out.println("2--购物车");
        System.out.println("0--退出");
        System.out.println("**********************************");
    }
    public void menu2() {
        System.out.println("**********************************");
        System.out.println("***商品管理***");
        System.out.println("1--商品信息导入");
        System.out.println("2--显示所有商品信息");
        System.out.println("9--返回上一级菜单");
        System.out.println("**********************************");
    }
    public void menu3() {
        System.out.println("**********************************");
        System.out.println("***购物车管理***");
        System.out.println("1--添加商品到购物车");
        System.out.println("2--修改购物车中的商品数量");
        System.out.println("3--显示购物车中的所有商品信息");
        System.out.println("4--结算");
        System.out.println("9--返回上一级菜单");
        System.out.println("**********************************");
    }
     
    public static void main(String[] args) {
        // TODO Auto-generated method stub
    boolean flag=false;
    TestDemo a=new TestDemo();
    GoodsManage b=new GoodsManage();
    ShoppingCart c=new ShoppingCart();
    Scanner sc=new Scanner(System.in);
    int n=0;
    while (flag=false) {
        a.menu();
        System.out.println("请输入相应的数字进行操作");
        n=sc.nextInt();
        flag=true;
        try {
            if(n<0||n>2) {
                System.out.println("您的输入有误，请重新输入！");
                flag=false;
                continue;
            }else {
                    switch(n) {
                    case 1:
                        while(flag=true) {
                            a.menu2();
                            System.out.println("请输入相应的数字进行操作");
                            if(n<1||n>2&&n!=9) {
                                System.out.println("您的输入有误，请重新输入！");
                                continue;
                            }else {
                                switch(n) {
                                case 1:
                                    b.importGoods();
                                    break;
                                case 2:
                                    b.displayAllGoods();
                                    break;
                                }
                            }
                            if(n==9) {
                                flag=false;
                                break;
                            }
                    }
                        break;
                    case 2:
                        while(flag=true) {
                            a.menu3();
                            System.out.println("请输入相应的数字进行操作");
                            n=sc.nextInt();
                            if(n<1||n>4&&n!=9) {
                                System.out.println("您的输入有误，请重新输入！");
                                continue;
                            }else {
                                switch(n) {
                                case 1:
                                    c.addGoodsToCart(b);
                                    break;
                                case 2:
                                    c.updateNumInCart();
                                    break;
                                case 3:
                                    c.displayAllInCart();
                                    break;
                                case 4:
                                    c.settleAccounts();
                                    break;
                                }
                            }
                            if(n==9) {
                                flag=false;
                                break;
                            }
                        }
                        break;
                    case 0:
                        System.out.println("***欢迎您下次光临***");
                        break;
                }
            }
        }catch(InputMismatchException an){
            System.out.println("你的输入有误，请重新输入！");
        }
    }
 
    }
}

独孤求戒 2019-03-05

源自：Java集合 5-2 作业题

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2回答

好帮手慕阿满回答被采纳获得+3积分 2019-03-05 14:54:25

同学你好，在同学的测试类的主方法中，while()循环时，while条件是flag = false是赋值语句，不是条件，所以不会执行循环，出现同学所说的没有反应，这里应该修改为==，如：

同学修改一下再试试。

如果我的回答解决了你的疑惑，请采纳。祝：学习愉快~

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独孤求戒提问者 #1

如果在测试类中，我用try catch语句，在提示输入数字时候，我输入字母时候，系统会捕获异常从而结束程序运行，我想请问老师，在输入了字母的情况下，如何修改代码才能使程序重新循环，再次执行到System.out.println("您的输入有误，请重新输入！");语句，使程序不结束，继续运行

2019-03-05 15:19:56

好帮手慕阿满 2019-03-05 16:58:19

public class Demo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个整数");
        while(true) {
            try {
                int n = sc.nextInt(); 
            }catch (Exception e) {
                System.out.println("您的输入有误，请重新输入！");
                sc.next();//接收错误的数据
                continue;
            }
        }
         
         
    }
}