java list 扁平化 java list优化

1.集合实体提取里面提起一个字段生成新的集合

List<Shop> shops = shopService.findList(searchParams);
 List<Long> ids = shops.stream().map(Shop::getShopId).collect(Collectors.toList());

2.给里面里面每个实体设置值

List<Banner> list2 = list.getList();
list2.forEach(t -> t.setBannerId(1L));

3.集合的过滤生成新数组

List<Integer> transactionsIds = transactions.parallelStream().
filter(t -> t.getType() == Transaction.GROCERY).
sorted(comparing(Transaction::getValue).reversed()).
map(Transaction::getId).
collect(toList());

4.集合的排序

List<RiderForm> datas = daydatas.stream().sorted(Comparator.comparing(RiderForm::getRiderName))
                .collect(Collectors.toList()); 
public class RiderForm implements Serializable, Comparable<RiderForm> {
　　 @Override
    public int compareTo(
            RiderForm o) {
        return riderName.compareTo(o.getRiderName());

    }　　　　 @Override
    public boolean equals(
            final Object obj) {
        if (obj == null) {
            return false;
        }
        final RiderForm rf = (RiderForm) obj;
        if (this == rf) {
            return true;
        } else {
            return (this.riderName.equals(rf.riderName) && (this.orderType == rf.orderType));
        }
    } @Override
    public int hashCode() {
        int hashno = 7;
        hashno = 13 * hashno + (riderName == null ? 0 : riderName.hashCode());
        return hashno;
    } 
}

5.遍历map

map.entrySet().forEach(entry -> System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue()));