public abstract class AbstractMap<K,V> implements Map<K,V>{
protected AbstractMap() {
}
}
AbstractMap实现了Map接口，Map接口定义的方法在AbstractMap上都有体现，就不具体分析Map了
public int size() {
return entrySet().size();
}
public boolean isEmpty() {
return size() == 0;
}
public abstract Set<Entry<K,V>> entrySet();
从上面两个方法可以看出，AbstractMap存储数据是用的Set<Entry<K,V»
下面看下Entry<K,V>这个接口
interface Entry<K,V> {
K getKey();
V getValue();
V setValue(V value);
boolean equals(Object o);
private static boolean eq(Object o1, Object o2) {
return o1 == null ? o2 == null : o1.equals(o2);
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map<?,?> m = (Map<?,?>) o;
if (m.size() != size())
return false;
try {
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext()) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
if (value == null) {
if (!(m.get(key)==null && m.containsKey(key)))
return false;
} else {
if (!value.equals(m.get(key)))
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
}
int hashCode();
public int hashCode() {
int h = 0;
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext())
h += i.next().hashCode();
return h;
}
public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> c1.getKey().compareTo(c2.getKey());
}
public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> c1.getValue().compareTo(c2.getValue());
}
public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
Objects.requireNonNull(cmp);
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
}
public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
Objects.requireNonNull(cmp);
return (Comparator<Map.Entry<K, V>> & Serializable)
(c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
}
可以看到，Entry类似于一个JavaBean，提供了get和set方法，其实对于其他Map比如HashMap、LinkedHashMap、TreeMap，存储数据都是用的Entry，只是Entry的组织形式不一样，比如HashMap用的就是数组+链表(jdk1.8后)+红黑树，TreeMap用的是二叉树，LinkedHashMap使用的是链表。
public boolean containsValue(Object value) {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (value==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getValue()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (value.equals(e.getValue()))
return true;
}
}
return false;
}
public boolean containsKey(Object key) {
Iterator<Map.Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return true;
}
}
return false;
}
public V get(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (key==null) {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
return e.getValue();
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
return e.getValue();
}
}
return null;
}
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
}
public void clear() {
entrySet().clear();
}
判断key和value是否存在的方法，以及插入和获取，都是通过对Entry进行迭代，比较简单，可以从上面看到，是允许插入key和value为null的键值对的
public V remove(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();
Entry<K,V> correctEntry = null;
if (key==null) {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (e.getKey()==null)
correctEntry = e;
}
} else {
while (correctEntry==null && i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
correctEntry = e;
}
}
V oldValue = null;
if (correctEntry !=null) {
oldValue = correctEntry.getValue();
i.remove();
}
return oldValue;
}
移除的方法也是通过迭代，找到要删除的键值对后，用迭代器的remove进行移除，并返回要移除键值对的值。
transient Set<K> keySet;
transient Collection<V> values;
public Set<K> keySet() {
Set<K> ks = keySet;
if (ks == null) {
ks = new AbstractSet<K>() {
public Iterator<K> iterator() {
return new Iterator<K>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public K next() {
return i.next().getKey();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean isEmpty() {
return AbstractMap.this.isEmpty();
}
public void clear() {
AbstractMap.this.clear();
}
public boolean contains(Object k) {
return AbstractMap.this.containsKey(k);
}
};
keySet = ks;
}
return ks;
}
public Collection<V> values() {
Collection<V> vals = values;
if (vals == null) {
vals = new AbstractCollection<V>() {
public Iterator<V> iterator() {
return new Iterator<V>() {
private Iterator<Entry<K,V>> i = entrySet().iterator();
public boolean hasNext() {
return i.hasNext();
}
public V next() {
return i.next().getValue();
}
public void remove() {
i.remove();
}
};
}
public int size() {
return AbstractMap.this.size();
}
public boolean isEmpty() {
return AbstractMap.this.isEmpty();
}
public void clear() {
AbstractMap.this.clear();
}
public boolean contains(Object v) {
return AbstractMap.this.containsValue(v);
}
};
values = vals;
}
return vals;
}
public abstract Set<Entry<K,V>> entrySet();
public String toString() {
Iterator<Entry<K,V>> i = entrySet().iterator();
if (! i.hasNext())
return "{}";
StringBuilder sb = new StringBuilder();
sb.append('{');
for (;;) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
sb.append(key == this ? "(this Map)" : key);
sb.append('=');
sb.append(value == this ? "(this Map)" : value);
if (! i.hasNext())
return sb.append('}').toString();
sb.append(',').append(' ');
}
}
protected Object clone() throws CloneNotSupportedException {
AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone();
result.keySet = null;
result.values = null;
return result;
}
最后AbstractMap中还有两个静态内部类，一个是可变的Entry，另一个是不可变的(这里的可不可变指的是value是否可变)，这两个类都实现了序列化接口
public static class SimpleEntry<K,V>
implements Entry<K,V>, java.io.Serializable
{
private static final long serialVersionUID = -8499721149061103585L;
private final K key;
private V value;
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Entry<? extends K, ? extends V> entry) {
this.key = entry.getKey();
this.value = entry.getValue();
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
public String toString() {
return key + "=" + value;
}
}
public static class SimpleImmutableEntry<K,V>
implements Entry<K,V>, java.io.Serializable
{
private static final long serialVersionUID = 7138329143949025153L;
private final K key;
private final V value;
public SimpleImmutableEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
this.key = entry.getKey();
this.value = entry.getValue();
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
throw new UnsupportedOperationException();
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
public String toString() {
return key + "=" + value;
}
}
