5-2购物车空指针异常

Question

package com.immo.car;

public class Goods {
   private   String   goodId;
   private   String goodName;
   private   double    price;
   private   String    goodDesp;
  
   Goods(String  goodId,String  goodName,double price,String goodDesp){
    this.goodId=goodId;
    this.goodName=goodName;
    this.price=price;
    this.goodDesp=goodDesp;
   }
   Goods(){
   
   }
public String getGoodId() {
 return goodId;
}
public void setGoodId(String goodId) {
 this.goodId = goodId;
}
public String getGoodName() {
 return goodName;
}
public void setGoodName(String goodName) {
 this.goodName = goodName;
}
public double getPrice() {
 return price;
}
public void setPrice(double price) {
 this.price = price;
}
public String getGoodDesp() {
 return goodDesp;
}
public void setGoodDesp(String goodDesp) {
 this.goodDesp = goodDesp;
}
@Override
public int hashCode() {
 final int prime = 31;
 int result = 1;
 result = prime * result + ((goodDesp == null) ? 0 : goodDesp.hashCode());
 result = prime * result + ((goodId == null) ? 0 : goodId.hashCode());
 result = prime * result + ((goodName == null) ? 0 : goodName.hashCode());
 long temp;
 temp = Double.doubleToLongBits(price);
 result = prime * result + (int) (temp ^ (temp >>> 32));
 return result;
}
@Override
public boolean equals(Object obj) {
 if (this == obj)
  return true;
 if (obj == null)
  return false;
 if (getClass() != obj.getClass())
  return false;
 Goods other = (Goods) obj;
 if (goodDesp == null) {
  if (other.goodDesp != null)
   return false;
 } else if (!goodDesp.equals(other.goodDesp))
  return false;
 if (goodId == null) {
  if (other.goodId != null)
   return false;
 } else if (!goodId.equals(other.goodId))
  return false;
 if (goodName == null) {
  if (other.goodName != null)
   return false;
 } else if (!goodName.equals(other.goodName))
  return false;
 if (Double.doubleToLongBits(price) != Double.doubleToLongBits(other.price))
  return false;
 return true;
}
@Override
public String toString() {
 return "[商品编号：" + goodId + ", 商品名称：" + goodName + ", 商品价钱："
   + price + ", 商品描述：" + goodDesp + "]";
}
  
}

package com.immo.car;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class GoodsManage {
        private  Set<Goods>  goodset;

  public Set getGoodset() {
   return goodset;
  }
 
  public GoodsManage() {
 // TODO Auto-generated constructor stub
         }
  
  public void setGoodset(Set goodset) {
   this.goodset = goodset;
  }
        Set   s=new HashSet();
  public   void   improtGoods(){
   Goods   goods1=new Goods("s1001","矿泉水",90,"娃哈哈私人订制矿泉水");
   Goods   goods2=new Goods("s1002","旺仔牛奶",100,"再看再看就把你喝掉");
   Goods   goods3=new Goods("s1003","薯片",40,"咔吱脆");
   Goods   goods4=new Goods("s1004","苹果",30,"糖心苹果");
   s.add(goods1);
   s.add(goods4);
   s.add(goods3);
   s.add(goods2);
   setGoodset(s);
  }
  public  void   displayAllGoods(){
  /*Iterator it= s.iterator();
  while (it.hasNext()) {
    System.out.println("目前："+it.next());
   
  }
*/ Set<Goods> set= this.getGoodset();
      for (Goods goods : set) {
  System.out.println(goods);
 }
  }
  
}

package com.immo.car;

public class GoodsInCart {
     private  Goods  goods;
     private  int num;
    
     GoodsInCart(Goods  goods,int num){
      this.goods=goods;
      this.num=num;
     }
    
     GoodsInCart(){
     
     }

 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;
 }

 @Override
 public String toString() {
  return "GoodsInCart [goods=" + goods + ", num=" + num + "]";
 }
    
    
}

package com.immo.car;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.Set;

public class ShopingCart {
      public   Map<String, GoodsInCart> map;
     
      Scanner   sc=new Scanner(System.in);
     Boolean  flag=true;
     GoodsInCart   inCa;
     int  num=0;
      public  void   addGoodsCart(GoodsManage gm){
      if (gm.s.isEmpty()) {
      System.out.println("请先导入数据"+gm.s.isEmpty());  
      }else {

           System.out.println("友情提示：");
             gm.displayAllGoods();
            
           System.out.println("请输入商品编号");
            String  id=sc.next();
          Set<Goods> set= gm.getGoodset();
           for (Goods  g : set) {
         if (g.getGoodId().equals(id)) {
      System.out.println("请输入数量");
      num=sc.nextInt();
         inCa=new  GoodsInCart(g, num);
             System.out.println("数量"+inCa.toString());
             System.out.println(g);
             map.put(id, inCa);
    // System.out.println(map.isEmpty());
   
  }
 }
    //System.out.println(it.next()); 
  }
 
 }
  public   void   Anset(){
   System.out.println("请输入商品编号");
   String  Goodsid=sc.next();
   
   Set<String> set=map.keySet();
   for (String st:set) {
    if (st.contains(Goodsid)) {
     System.out.println("请输入数量");
     num=sc.nextInt();
     if (num==0) {
      map.remove(st);
     }
    }
   }
   
   
  }
  
  public   void   balanceGoods(){
  Collection<GoodsInCart> c= map.values();
  for (GoodsInCart goodsInCart : c) {
  double  price= goodsInCart.getNum()*goodsInCart.getGoods().getPrice();
  System.out.println("共计："+price);
  }
  }
 }
     
 

import java.util.Iterator;
import java.util.Set;

public class Test {
        public static void main(String[] args) {
         Goods  sGoods=new Goods();
   ShopingCart  s=new ShopingCart();
   //GoodsInCart  inCart=new  GoodsInCart();
       GoodsManage  manage=new GoodsManage();
    
       manage.improtGoods();
  Set<Goods> set= manage.getGoodset();
  for (Goods goods : set) {
   System.out.println(goods);
  }
   //manage.displayAllGoods();
   s.addGoodsCart(manage);
  }
}

Answer 1

首先来看报错位置，ShopingCart的31行；从这里可以看到是你的map出问题了，上下检查之后发现，map是ShopingCart的成员属性，但是，你在Shoping类中仅仅是定义了一个map属性，但是map没有进行初始化，所以不能直接调用put的方法进行添加键值对的操作，请同学对map进行初始化之后，再进行添加操作！祝，学习顺利！