读EnumMap源码

//一个key是枚举类型的map,速度基本会比hashMap更快
//先看构造函数

//构造指定键类型的EnumMap
public EnumMap(Class<K> keyType) {
        this.keyType = keyType;
	//获取key的枚举值
        keyUniverse = getKeyUniverse(keyType);
        vals = new Object[keyUniverse.length];
    }

public EnumMap(EnumMap<K, ? extends V> m) {
        keyType = m.keyType;
        keyUniverse = m.keyUniverse;
        vals = m.vals.clone();
        size = m.size;
    }

   public EnumMap(Map<K, ? extends V> m) {
        if (m instanceof EnumMap) {
            EnumMap<K, ? extends V> em = (EnumMap<K, ? extends V>) m;
            keyType = em.keyType;
            keyUniverse = em.keyUniverse;
            vals = em.vals.clone();
            size = em.size;
        } else {
            if (m.isEmpty())
                throw new IllegalArgumentException("Specified map is empty");
            //获取key的class类型
            keyType = m.keySet().iterator().next().getDeclaringClass();
            keyUniverse = getKeyUniverse(keyType);
            vals = new Object[keyUniverse.length];
            putAll(m);
        }
    }

//插入值
 public V put(K key, V value) {
        //验证key的class类型
        typeCheck(key);
        //获取枚举的位置
        int index = key.ordinal();
        Object oldValue = vals[index];
        vals[index] = maskNull(value);
        if (oldValue == null)
            size++;
        return unmaskNull(oldValue);
    }

//判断key的class类型
private void typeCheck(K key) {
        Class keyClass = key.getClass();
        if (keyClass != keyType && keyClass.getSuperclass() != keyType)
            throw new ClassCastException(keyClass + " != " + keyType);
    }

//通过key获取值
public V get(Object key) {
        return (isValidKey(key) ?
                unmaskNull(vals[((Enum)key).ordinal()]) : null);
    }

//校验key
private boolean isValidKey(Object key) {
        if (key == null)
            return false;

        // Cheaper than instanceof Enum followed by getDeclaringClass
        Class keyClass = key.getClass();
        return keyClass == keyType || keyClass.getSuperclass() == keyType;
    }

//根据key删除值
public V remove(Object key) {
        if (!isValidKey(key))
            return null;
        int index = ((Enum)key).ordinal();
        Object oldValue = vals[index];
        vals[index] = null;
        if (oldValue != null)
            size--;
        return unmaskNull(oldValue);
    }

//删除映射
private boolean removeMapping(Object key, Object value) {
        if (!isValidKey(key))
            return false;
        int index = ((Enum)key).ordinal();
        if (maskNull(value).equals(vals[index])) {
            vals[index] = null;
            size--;
            return true;
        }
        return false;
    }

//返回集合长度
 public int size() {
        return size;
    }

//是否包含某个key
public boolean containsKey(Object key) {
        return isValidKey(key) && vals[((Enum)key).ordinal()] != null;
    }

//是否包含某个值
 public boolean containsValue(Object value) {
        value = maskNull(value);

        for (Object val : vals)
            if (value.equals(val))
                return true;

        return false;
    }

//清空
public void clear() {
        Arrays.fill(vals, null);
        size = 0;
    }

//添加所有的
public void putAll(Map<? extends K, ? extends V> m) {
        if (m instanceof EnumMap) {
            EnumMap<? extends K, ? extends V> em =
                (EnumMap<? extends K, ? extends V>)m;
            if (em.keyType != keyType) {
                if (em.isEmpty())
                    return;
                throw new ClassCastException(em.keyType + " != " + keyType);
            }

            for (int i = 0; i < keyUniverse.length; i++) {
                Object emValue = em.vals[i];
                if (emValue != null) {
                    if (vals[i] == null)
                        size++;
                    vals[i] = emValue;
                }
            }
        } else {
            super.putAll(m);
        }
    }