为什么会出现空指针异常= =

如下图所示，建议你在GoodsManager类中创建一个set集合，按下图修改就会在类加载的时候创建set集合，如果不创建set集合，只是声明set，那么在使用set集合的时候就会出现空指针异常，如果我的建议解决了你的问题，请采纳，祝学习愉快~

package com.imooc.marketManager;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;

public class GoodsManage {

// 存放商品的容器

private Set<Goods> goodsSet;

public GoodsManage() {

}

public GoodsManage(HashSet<Goods> goodsSet) {

this.setGoodsSet(goodsSet);

}

public Set<Goods> getGoodsSet() {

return goodsSet;

}

public void setGoodsSet(Set<Goods> goodsSet) {

this.goodsSet = goodsSet;

}

public void importGoods() {

Goods one = new Goods("goods001", "水杯", 56, "不锈钢水杯");

Goods two = new Goods("goods002", "饮水机", 299, "带净化功能的饮水机");

Goods three = new Goods("goods003", "笔记本电脑", 4999, "15寸笔记本");

Goods four = new Goods("goods004", "手机", 2300, "android手机");

goodsSet.add(one);

goodsSet.add(two);

goodsSet.add(three);

goodsSet.add(four);

System.out.println("商品导入成功!");

}

public void displayAllGoods() {

if (goodsSet.isEmpty()) {

System.out.println("商品还未导入，请先导入商品信息");

} else {

Iterator<Goods> it = goodsSet.iterator();

System.out.println("所有商品信息");

while (it.hasNext()) {

System.out.println(it.next());

}

}

}

}