遍历List集合和Map集合的几种方式

# 遍历Map集合

三种方式：

1）map.keySet()

Map<String,String> map = new TreeMap<>();
		map.put("k1","v1");
		map.put("k2","k2");
		map.put("k3","k3");
		map.put("k4","v4");

		//第一种
		for (String key : map.keySet()) {
			System.out.println(key + " " + map.get(key));
		}

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2）map.entrySet()

Map<String,String> map = new TreeMap<>();
		map.put("k1","v1");
		map.put("k2","k2");
		map.put("k3","k3");
		map.put("k4","v4");

        //第二种
		for (Map.Entry<String, String> entry : map.entrySet()) {
			System.out.println(entry);
		}

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3）map.entrySet().iterator()

Map<String,String> map = new TreeMap<>();
		map.put("k1","v1");
		map.put("k2","k2");
		map.put("k3","k3");
		map.put("k4","v4");

        //第三种
		Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
		while (iterator.hasNext()){
			Map.Entry<String, String> entry = iterator.next();
			System.out.println(entry);
		}

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# 遍历List集合

四种方式：

1）list.size()

List<String> list = new ArrayList<>();

		list.add("k1");
		list.add("k2");
		list.add("k3");
		list.add("k4");

		//第一种
		for (int i = 0; i < list.size(); i++) {
			System.out.println(list.get(i));
		}

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2）list

List<String> list = new ArrayList<>();

		list.add("k1");
		list.add("k2");
		list.add("k3");
		list.add("k4");


		//第二种
		for (String str : list) {
			System.out.println(str);
		}

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3）list.forEach

List<String> list = new ArrayList<>();

		list.add("k1");
		list.add("k2");
		list.add("k3");
		list.add("k4");

		//第三种
		list.forEach(s-> System.out.println(s));

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4）list.iterator()

List<String> list = new ArrayList<>();

		list.add("k1");
		list.add("k2");
		list.add("k3");
		list.add("k4");


		//第四种
		Iterator<String> iterator = list.iterator();
		while (iterator.hasNext()){
			String str = iterator.next();
			System.out.println(str);
		}

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