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valuesfor (String v : map.values()) {System.out.println(v);}map.values().forEach(System.out::println);// Java8 Lambdamap.forEach((k, v) -> System.out.println(k + " ==> " + v));
Map转List
@Data@NoArgsConstructor@AllArgsConstructorclass KeyValue {private Integer key;private String value;@Overridepublic 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 ListList<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 ListList<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ListList<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 StreamList<KeyValue> list = map.entrySet().stream().map(c -> new KeyValue(c.getKey(), c.getValue())).collect(Collectors.toList());list.forEach(System.out::println);
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 StreamMap<Integer, String> map = list.stream().collect(Collectors.toMap(KeyValue::getKey, KeyValue::getValue));map.forEach((k, v) -> System.out.println(k + " ==> " + v));
