EnumMap（A Guide to EnumMap）

╰+哭是因爲堅強的太久メ 2024-03-23 17:38 12阅读 0赞

###  ###

public enum DayOfWeek {
        
        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
    }

### Creation ###

EnumMap<DayOfWeek, String> activityMap = new EnumMap<>(DayOfWeek.class);
    activityMap.put(DayOfWeek.MONDAY, "Soccer");
    activityMap.put(DayOfWeek.TUESDAY, "Basketball");

### EnumMap Copy Constructor ###

EnumMap<DayOfWeek, String> activityMap = new EnumMap<>(DayOfWeek.class);
    activityMap.put(DayOfWeek.MONDAY, "Soccer");
    activityMap.put(DayOfWeek.TUESDAY, "Basketball");
    
    EnumMap<DayOfWeek, String> activityMapCopy = new EnumMap<>(activityMap);
    
    System.out.println(activityMapCopy.size()); // 2
    System.out.println(activityMapCopy.get(DayOfWeek.MONDAY)); // Soccer

### Map Copy Constructor ###

Map<DayOfWeek, String> ordinaryMap = new HashMap();
    ordinaryMap.put(DayOfWeek.MONDAY, "Soccer");
    
    EnumMap enumMap = new EnumMap(ordinaryMap);
    
    System.out.println(activityMapCopy.size()); // 2
    System.out.println(activityMapCopy.get(DayOfWeek.MONDAY)); // Soccer

### 基础方法 ###

ordinaryMap.put(DayOfWeek.MONDAY, "Soccer");
    
    activityMapCopy.get(DayOfWeek.MONDAY)
    
    ordinaryMap.containsKey(DayOfWeek.MONDAY)
    
    ordinaryMap.size()

### null as Value ###

EnumMap<DayOfWeek, String> activityMap = new EnumMap<>(DayOfWeek.class);
    activityMap.put(DayOfWeek.MONDAY, "Soccer");
    activityMap.put(DayOfWeek.TUESDAY, "Basketball");
    
    System.out.println(activityMap.containsKey(DayOfWeek.SATURDAY)); // false
    System.out.println(activityMap.containsValue(null)); // false
    
    activityMap.put(DayOfWeek.SATURDAY, null);
    System.out.println(activityMap.containsKey(DayOfWeek.SATURDAY)); // true
    System.out.println(activityMap.containsValue(null)); // true

### Removing Elements ###

activityMap.put(DayOfWeek.MONDAY, "Soccer");
    System.out.println(activityMap.remove(DayOfWeek.MONDAY, "Hiking")); // false
    System.out.println(activityMap.remove(DayOfWeek.MONDAY, "Soccer")); // true

### values、keySet、entrySet ###

EnumMap<DayOfWeek, String> activityMap = new EnumMap<>(DayOfWeek.class);
    activityMap.put(DayOfWeek.MONDAY, "Soccer");
    activityMap.put(DayOfWeek.TUESDAY, "Basketball");
    
    Collection<String> values = activityMap.values();
    
    Set<DayOfWeek> dayOfWeeks = activityMap.keySet();
    
    Set<Map.Entry<DayOfWeek, String>> entries = activityMap.entrySet();

\-----------------------------------------------------------------------------读书笔记摘自 文章：[A Guide to EnumMap][]

[A Guide to EnumMap]: https://www.baeldung.com/java-enum-map