1. 遍历Map

Map<Integer, String> map = new HashMap<>();

map.put(1, "a");

map.put(2, "b");

map.put(3, "c");

// Map.keySet遍历

for (Integer k : map.keySet()) {

	System.out.println(k + " ==> " + map.get(k));

}

map.keySet().forEach(k -> System.out.println(k + " ==> " + map.get(k)));

// Map.entrySet遍历，推荐大容量时使用

for (Map.Entry<Integer, String> entry : map.entrySet()) {

	System.out.println(entry.getKey() + " ==> " + entry.getValue());

}

map.entrySet().forEach(entry -> System.out.println(entry.getKey() + " ==> " + entry.getValue()));

// Iterator遍历

Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();

while (it.hasNext()) {

	Map.Entry<Integer, String> entry = it.next();

	System.out.println(entry.getKey() + " ==> " + entry.getValue());

}

map.entrySet().iterator()

		.forEachRemaining(entry -> System.out.println(entry.getKey() + " ==> " + entry.getValue()));

// 遍历values

for (String v : map.values()) {

	System.out.println(v);

}

map.values().forEach(System.out::println);

// Java8 Lambda

map.forEach((k, v) -> System.out.println(k + " ==> " + v));

2. Map转List

@Data

@NoArgsConstructor

@AllArgsConstructor

class KeyValue {

	private Integer key;

	private String value;

	@Override

	public String toString() {

		return key + " ==> " + value;

	}

}

Map<Integer, String> map = new HashMap<>();

map.put(1, "a");

map.put(2, "b");

map.put(3, "c");

// key 转 List

List<Integer> keyList = new ArrayList<>(map.keySet());

List<Integer> keyList2 = map.keySet().stream().collect(Collectors.toList());

keyList.forEach(System.out::println);

keyList2.forEach(System.out::println);

// value 转 List

List<String> valueList = new ArrayList<>(map.values());

List<String> valueList2 = map.values().stream().collect(Collectors.toList());

valueList.forEach(System.out::println);

valueList2.forEach(System.out::println);

// Iterator转List

List<KeyValue> keyValueList = new ArrayList<>();

Iterator<Integer> it = map.keySet().iterator();

while (it.hasNext()) {

	Integer k = (Integer) it.next();

	keyValueList.add(new KeyValue(k, map.get(k)));

}

keyValueList.forEach(System.out::println);

// Java8 Stream

List<KeyValue> list = map.entrySet().stream().map(c -> new KeyValue(c.getKey(), c.getValue()))

		.collect(Collectors.toList());

list.forEach(System.out::println);

3. List转Map

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

list.add(new KeyValue(1, "a"));

list.add(new KeyValue(2, "b"));

list.add(new KeyValue(3, "c"));

// 遍历

Map<Integer, String> keyValueMap = new HashMap<>();

for (KeyValue keyValue : list) {

	keyValueMap.put(keyValue.getKey(), keyValue.getValue());

}

keyValueMap.forEach((k, v) -> System.out.println(k + " ==> " + v));

// Java8 Stream

Map<Integer, String> map = list.stream().collect(Collectors.toMap(KeyValue::getKey, KeyValue::getValue));

map.forEach((k, v) -> System.out.println(k + " ==> " + v));