AbstractMap 提供 Map 接口的骨干实现，以最大限度地减少实现此接口所需的工作。
//实现了接口Map
public abstract class AbstractMap<K,V> implements Map<K,V> {
protected AbstractMap() {//提供一个空的构造函数
}
public int size() {//返回元素个数
return entrySet().size();//通过entrySet()方法获得元素集合
}
public boolean isEmpty() {
return size() == 0;//判断是否为空
}
//判断是否包含值为value的元素，这里的实现是根据迭代器来判断的
public boolean containsValue(Object value) {
Iterator<Entry<K,V>> i = entrySet().iterator();//获得元素集合的迭代器
if (value==null) {//value为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()))//这里比较的是内容
return true;
}
}
return false;
}
//判断是否包含key为key的元素，这里也是通过元素集合的迭代器来判断
public boolean containsKey(Object key) {
Iterator<Map.Entry<K,V>> i = entrySet().iterator();//获得元素集合的迭代器
if (key==null) {//key为null
while (i.hasNext()) {
Entry<K,V> e = i.next();//迭代器获得Entry类型的元素
if (e.getKey()==null)
return true;
}
} else {
while (i.hasNext()) {
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))//这里比较的也是内容
return true;
}
}
return false;
}
//获得key为key的值，这里的实现和上面两个方法类似
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;
}
//添加元素方法，这里未实现
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
//删除key为key的元素
public V remove(Object key) {
Iterator<Entry<K,V>> i = entrySet().iterator();//获得迭代器
Entry<K,V> correctEntry = null;
if (key==null) {
while (correctEntry==null && i.hasNext()) {//找到元素
Entry<K,V> e = i.next();
if (e.getKey()==null)
correctEntry = e;
}
} else {
while (correctEntry==null && i.hasNext()) {//找到元素
Entry<K,V> e = i.next();
if (key.equals(e.getKey()))
correctEntry = e;
}
}
V oldValue = null;
if (correctEntry !=null) {
oldValue = correctEntry.getValue();
i.remove();//通过迭代器的remove方法删除
}
return oldValue;
}
//添加所有元素
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());//循环调用Put方法
}
//删除所有元素
public void clear() {
entrySet().clear();
}
transient volatile Set<K> keySet = null;//key的集合
transient volatile Collection<V> values = null;//values的集合
//返回key的集合
public Set<K> keySet() {
if (keySet == null) {//如果为空
keySet = new AbstractSet<K>() {//key的类型为AbstractSet
public Iterator<K> iterator() {//实现其迭代器接口
return new Iterator<K>() {//匿名内部类
private Iterator<Entry<K,V>> i = entrySet().iterator();//获得Entry集合的迭代器
public boolean hasNext() {//判断是否有元素
return i.hasNext();
}
public K next() {//获得元素的key
return i.next().getKey();
}
public void remove() {//删除元素
i.remove();
}
};
}
public int size() {//返回元素个数
return AbstractMap.this.size();
}
public boolean isEmpty() {//判断元素是否为空
return AbstractMap.this.isEmpty();
}
public void clear() {//清楚元素
AbstractMap.this.clear();
}
public boolean contains(Object k) {//判断是否有键值为k的元素
return AbstractMap.this.containsKey(k);//调用父类的方法来判断
}
};
}
return keySet;
}
//返回所有值的集合，实现和上面类似，请参考
public Collection<V> values() {
if (values == null) {
values = new AbstractCollection<V>() {
public Iterator<V> iterator() {//迭代器接口
return new Iterator<V>() {//匿名内部类，迭代器
private Iterator<Entry<K,V>> i = entrySet().iterator();//获得Entry集合的迭代器
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);
}
};
}
return values;
}
//返回Entry的集合。
public abstract Set<Entry<K,V>> entrySet();
//判断元素是否相等的方法
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Map))
return false;
Map<K,V> m = (Map<K,V>) o;
if (m.size() != size())
return false;
try {
Iterator<Entry<K,V>> i = entrySet().iterator();//通过迭代器判断
while (i.hasNext()) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
if (value == null) {//值为null
if (!(m.get(key)==null && m.containsKey(key)))//判断m中是否不存在对应的key和alue
return false;
} else {
if (!value.equals(m.get(key)))
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
}
public int hashCode() {
int h = 0;
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext())
h += i.next().hashCode();//每个Entry的hash之和
return h;
}
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(‘ ‘);
}
}
//Clone方法
protected Object clone() throws CloneNotSupportedException {
AbstractMap<K,V> result = (AbstractMap<K,V>)super.clone();
result.keySet = null;//key为空
result.values = null;//value为空
return result;
}
//判断对象是否相等
private static boolean eq(Object o1, Object o2) {
return o1 == null ? o2 == null : o1.equals(o2);
}
//Entry接口的实现，是二元组的简单操作
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;
}
}
//只读Entry的实现，只是取消了修改Entry的方法
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;
}
//不支持设置值的方法
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;
}
}
}