功能:

表述1：從輸入中找出parent相同的name，輸出為output格式

表述2：從輸入中，尋找連結串列關係。parent-->name。

input

List<Industry> all = new ArrayList<>();
		all.add(new Industry("a", null, Level.one));
		all.add(new Industry("b", null, Level.one));
		all.add(new Industry("1", "a", Level.two));
		all.add(new Industry("2", "a", Level.two));
		all.add(new Industry("3", "a", Level.two));
		all.add(new Industry("4", "b", Level.two));
		all.add(new Industry("5", "b", Level.two));
		all.add(new Industry("6", "b", Level.two));
 

output

{a=[1, 2, 3], b=[4, 5, 6]}

菜鳥：

public static Map<String, List<String>> hello() {
		List<Industry> all = new ArrayList<>();
		all.add(new Industry("a", null, Level.one));
		all.add(new Industry("b", null, Level.one));
		all.add(new Industry("1", "a", Level.two));
		all.add(new Industry("2", "a", Level.two));
		all.add(new Industry("3", "a", Level.two));
		all.add(new Industry("4", "b", Level.two));
		all.add(new Industry("5", "b", Level.two));
		all.add(new Industry("6", "b", Level.two));
		
		List<Industry> list = new ArrayList<>();
		for(Industry industry : all)
			if(industry.getParent() != null)
				list.add(industry);
		if(list.isEmpty())
			return null;
		Map<String, List<String>> mm = new HashMap<>();
		for(Industry industry : list) {
			Set<String> ls = new HashSet<>();
			for(Industry industrys : list) 
				if(industry.getParent().equals(industrys.getParent())) {
					ls.add(industrys.getName());
					ls.add(industry.getName());
				}
			
			mm.put(industry.getParent(),new ArrayList<>(ls));
		}
		System.out.println(mm);
		return mm;
	}
 

大神：

public static Map<String, List<String>> hello0() {
		List<Industry> all = new ArrayList<>();
		all.add(new Industry("a", null, Level.one));
		all.add(new Industry("b", null, Level.one));
		all.add(new Industry("1", "a", Level.two));
		all.add(new Industry("2", "a", Level.two));
		all.add(new Industry("3", "a", Level.two));
		all.add(new Industry("4", "b", Level.two));
		all.add(new Industry("5", "b", Level.two));
		all.add(new Industry("6", "b", Level.two));

		Map<String, List<String>> map = new HashMap<>();
		for (Industry i : all) {
			if (!StringUtils.isEmpty(i.getParent())) {
				List<String> temp = map.get(i.getParent());
				if (temp == null) {
					temp = new ArrayList<>();
					temp.add(i.getName());
					map.put(i.getParent(), temp);
				} else {
					temp.add(i.getName());
				}
			}

		}
		System.out.println(map);
		return map;
	}