关于List存储对象问题

写项目时遇到了一个bug关于List循环储存对象的问题

部分代码截取如下：

          IndexCategoryVO thirdLevelCategoryVO = new IndexCategoryVO();
        for (GoodsCategory goodsCategory : tempGoodsCategories){
            thirdLevelCategoryVO.setCategoryId(goodsCategory.getCategoryId());
            thirdLevelCategoryVO.setCategoryLevel(goodsCategory.getCategoryLevel());
            thirdLevelCategoryVO.setCategoryName(goodsCategory.getCategoryName());
            thirdLevelCategoryVO.setParentId(goodsCategory.getParentId());
            thirdLevelCategoryVO.setCategoryRank(goodsCategory.getCategoryRank());

            thirdLevelCategoryVOS.add(thirdLevelCategoryVO);
        }

问题：循环后thirdLevelCategoryVOS集合里面全是保存相同的对象，本应该都不同

解决：如下，把此行代码放入循环内，

IndexCategoryVO thirdLevelCategoryVO = new IndexCategoryVO();

for (GoodsCategory goodsCategory : tempGoodsCategories){
            IndexCategoryVO thirdLevelCategoryVO = new IndexCategoryVO();
            thirdLevelCategoryVO.setCategoryId(goodsCategory.getCategoryId());
            thirdLevelCategoryVO.setCategoryLevel(goodsCategory.getCategoryLevel());
            thirdLevelCategoryVO.setCategoryName(goodsCategory.getCategoryName());
            thirdLevelCategoryVO.setParentId(goodsCategory.getParentId());
            thirdLevelCategoryVO.setCategoryRank(goodsCategory.getCategoryRank());

            thirdLevelCategoryVOS.add(thirdLevelCategoryVO);
        }

原因：List中存储的是对象的地址

 

总结：List中存储的是对象的地址，如果将对象清楚，从List中取出来的对象也为空值