List根据条件删除元素的几种方式

   Iterator<Project> it = projectList.iterator();
            while(it.hasNext()){
                Project p=it.next();
                if (!allProjectMap.containsKey(p.getId())){
                    it.remove();
                };
            }

public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("aa");
        list.add("bb");
        list.add("cc");
        for (int i = list.size() - 1; i >= 0; i--) {
            String str = list.get(i);
            if ("aa".equals(str)) {
                list.remove(str);
            }
        }
        System.out.println(list.size());
    }
}

public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("aa");
        list.add("bb");
        list.add("cc");
        CopyOnWriteArrayList<String> cowList = new CopyOnWriteArrayList<String>(list);
        for (String str : cowList) {
            if ("aa".equals(str)) {
                cowList.remove(str);
            }
        }
        System.out.println(cowList.size());
    }
}

 for (int i = projectList.size() - 1; i >= 0; i--) {
                    for (int j = projectList.size() - 1; j >= 0; j--) {
                        if (projectList.get(i).getId().equals(projectList.get(j).getId())) {
                            if (projectList.get(i).getHigh() != null && projectList.get(j).getHigh() != null) {
                                if (projectList.get(i).getHigh() > projectList.get(j).getHigh()) {
                                    projectList.remove(j);
                                    i-=1;
                                }
                            }
                        }
                    }
                }

list.removeAll(Collections.singleton(null));

list.removeIf(Objects::isNull);

 List<String> newList = list.stream().filter(Objects::nonNull).collect(Collectors.toList());