集合的遍历以及排序

一.List的遍历和排序

	List<Integer> list = new ArrayList<Integer>();
	list.add(11);
	list.add(1);
	list.add(12);
	list.add(5);
	
	System.out.println("-------for循环遍历----------");
	for (int i =0;i<list.size();i++){
		System.out.println(list.get(i));
	}
	System.out.println("---------foreach遍历--------");
	for(Integer i:list){
		System.out.println(i);
	}
	System.out.println("-----------------");
	// 排序方式1
	Collections.sort(list); //升序
	//降序
	Collections.sort(list, new Comparator<Integer>(){
		@Override
		public int compare(Integer o1,Integer o2){
			return o2 - o1;
		}
	});
	for(Integer i :list ){
		System.out.println(i);
	}
	System.out.println("-----------------");
	//排序方式2
	List<Integer> list2 = list.stream().sorted(new Comparator<Integer>(){
		@Override
		public int compare(Integer o1,Integer o2){
			return o1 -o2;
		}
	}).collect(Collectors.toList());

	for(Integer i :list2 ){
		System.out.println(i);
	}
	System.out.println("-----------------");

二.set的排序和遍历

	Set<Integer> set = new TreeSet<Integer>(new Comparator<Integer>(){
		@Override
		public int compare(Integer o1,Integer o2){
			return o1 - o2;
		}
	});
	set.add(12);
	set.add(4);
	set.add(2);
	set.add(17);


	//遍历方式1
	for(Integer i :set){
		System.out.println(i);
	}
	System.out.println("========================");
	// 遍历方式2
	Iterator<Integer> iterator = set.iterator();
	while(iterator.hasNext()){
		System.out.println(iterator.next());
	}

三 Map的排序遍历

	Map<Integer,String> map = new HashMap<Integer,String>();
	map.put(2,"c");
	map.put(5,"f");
	map.put(1,"d");
	map.put(7,"e");
	map.put(4,"c");

	//遍历方式1
	for(Map.Entry<Integer,String> m:map.entrySet()){
		System.out.println(m.getKey()+"-------"+m.getValue());
	}
	System.out.println("-----------1--------------");
	
	//遍历方式2
	for (Integer i : map.keySet()){
		System.out.println(i +"---------"+map.get(i));
	}
	System.out.println("-----------2--------------");
	
	// 遍历方式3
	Iterator<Map.Entry<Integer,String>> iterator = map.entrySet().iterator();
	while(iterator.hasNext()){
		Map.Entry<Integer,String> item = iterator.next();
			System.out.println(item .getKey()+"-------"+item.getValue());
	}
	System.out.println("-----------3--------------");

	//按key排序
	LinkedHashMap<Integer,String> m = map.entrySet().stream().sorted(Map.Entry.comparingByKey())
										.collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue,(oldVal,newVal)->oldVal,LinkedHashMap::new));

	for(Map.Entry<Integer,String> i :m.entrySet()){
		System.out.println(i.getKey()+"---"+i.getValue());
	}
	System.out.println("-----------4--------------");
	//按value排序
	LinkedHashMap<Integer,String> m2 = map.entrySet().stream().sorted(Map.Entry.comparingByValue())
						.collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue,(oldVal,newVal)->oldVal,LinkedHashMap::new));
						
	for(Map.Entry<Integer,String> i :m2.entrySet()){
		System.out.println(i.getKey()+"---"+i.getValue());
	}
	System.out.println("-----------5--------------");

四 TreeMap默认只能按key排序

	Map<Integer,String> map = new TreeMap<Integer,String>(new Comparator<Integer>() {

		@Override
		public int compare(Integer o1, Integer o2) {
			return o2 -o1;
		}
	});
	map.put(2,"c");
	map.put(5,"f");
	map.put(1,"d");
	map.put(7,"e");
	map.put(4,"c");

	Iterator<Entry<Integer, String>> iterator = map.entrySet().iterator();
	while(iterator.hasNext()){
		Map.Entry<Integer, String> item = iterator.next();
		System.out.println(item.getKey()+"----"+item.getValue());
	}

来源：CSDN

作者：plcxtch1234

链接：https://blog.csdn.net/qq_36620250/article/details/104411967