集合常用方法

Iterator循环删除list中元素

for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); ) {
        String str=iterator.next();
        if (Objects.equals("one",str)){
            iterator.remove();
        }
    }
// or
Iterator<String> iterator = list.iterator();
    while(iterator.hasNext()){
        String str=iterator.next();
        if (Objects.equals("one",str)){
            iterator.remove();
        }

集合转成字符串逗号分隔

StringUtils.join(list,",");

取集合中最大值

long parValueMax = Collections.max(resultList.stream().map(OmsCouponUserAppVo::getParValue).collect(Collectors.toList()));

字符串根据逗号转成List

List<String> items = Arrays.asList(str.split("\\s*,\\s*"));

集合去重

items.stream().distinct().collect(Collectors.joining(","));

对对象集合中的某字段降序排序

Collections.sort(list, new Comparator<OmsCouponSend>() {
    @Override
    public int compare(OmsCouponSend o1, OmsCouponSend o2) {
        if (o1.getCoupon() > o2.getCoupon()) {
            return -1;
        }
        if (o1.getCoupon().equals(o2.getCoupon())) {
            return 0;
        }
        return 1;
    }
});

对集合中某元素去重

ArrayList<OmsCollectAppVo> distinctLiost = resultList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparingLong(OmsCollectAppVo::getSortId))), ArrayList::new));

多条件对集合排序

(如果a1-a2大于0，返回正数是升序;如果a2-a1小于0，返回负数是降序)

Collections.sort(students, new Comparator(){

  public int compare(Student a1, Student a2) {

     int x = a1.getAge() - a2.getAge();

  int y = a1.getSalary() - a2.getSalary();

     int z = a1.getHeight() - a2.getHeight();

  if(x==0){

  if(y==0){

  return z;

  }

  return y;

  }

  return x;

  }

  });

​