AbstractMap總結:
1.AbsrtactMap是其他Map具體實作類的骨架實作
2.AbstractMap實作Map接口,主要是對Map接口中的抽象方法進行重寫,個别方法因為子類的不同特性在子類中進行具體實作實作
3.在AbstractMap中,隻沒有對put()方法進行重寫。
4.在AbstractMap中,提供了兩種Entry,可變Entry和不可變Entry,這兩種均實作Map.Entry接口, SimpleEntry和SimpleImmutableEntry,SimpleEntry是中key變量不可變,SimpleImmutableEntry的key,value變量均不可變(final修飾),兩者的equals()和hashcode()實作相同
package com.xz.concurrent.collection;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
public abstract class AbstractMap<K, V> implements Map<K, V> {
/*------------------------構造---------------------------*/
protected AbstractMap() {
}
/*-------------------------重寫Map方法-----------------------------*/
/**
* 隻要周遊 底層均使用Set<Map.Entry<K,V>> = entrySet()的疊代器iterator
*/
@Override
public int size() {
return entrySet().size();
}
@Override
public boolean isEmpty() {
return size() == 0;
}
@Override
public boolean containsValue(Object value) {
Iterator<Entry<K, V>> i = entrySet().iterator();
//value == null 時查找 null不能計算hashcode
if (value == null) {
while (i.hasNext()) {
Entry<K, V> e = i.next();
//value(Object)
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;
}
/**
* 邏輯同containValue() 根據兩種情況 key == null key!=null
*/
@Override
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;
}
/**
* 根據key == null key != null
*/
@Override
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;
}
//未實作 由子類實作
@Override
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
@Override
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();
//疊代器删除
i.remove();
}
return oldValue;
}
@Override
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
@Override
public void clear() {
entrySet().clear();
}
/*-------------------------三種視圖實作---------------------------*/
transient Set<K> keySet;
transient Collection<V> values;
/**
* keySet()、values()方法的内部實作相似
* @return
*/
@Override
public Set<K> keySet() {
Set<K> ks = keySet;
//初始化set集合
if (ks == null) {
ks = new AbstractSet<K>() {
/*--------------重寫AbstractSet方法---------------*/
@Override
public Iterator<K> iterator() {
return new Iterator<K>() {
private Iterator<Entry<K, V>> i = entrySet().iterator();
/*-----------重寫Iterator方法-----------*/
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public K next() {
return i.next().getKey();
}
@Override
public void remove() {
i.remove();
}
};
}
@Override
public int size() {
return AbstractMap.this.size();
}
@Override
public boolean isEmpty() {
return AbstractMap.this.isEmpty();
}
@Override
public void clear() {
AbstractMap.this.clear();
}
@Override
public boolean contains(Object k) {
return containsKey(k);
}
};
//給keySet進行指派
keySet = ks;
}
return ks;
}
@Override
public Collection<V> values() {
Collection<V> vals = values;
//初始化vals
if (vals == null) {
vals = new AbstractCollection<V>() {
@Override
public Iterator<V> iterator() {
return new Iterator<V>() {
private Iterator<Entry<K, V>> i = entrySet().iterator();
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public V next() {
return i.next().getValue();
}
@Override
public void remove() {
i.remove();
}
};
}
@Override
public int size() {
return AbstractMap.this.size();
}
@Override
public boolean isEmpty() {
return AbstractMap.this.isEmpty();
}
@Override
public void clear() {
AbstractMap.this.clear();
}
@Override
public boolean contains(Object v) {
return containsValue(v);
}
};
//給values進行指派
values = vals;
}
return vals;
}
@Override
public abstract Set<Map.Entry<K, V>> entrySet();
/*----------------------重寫Object方法------------------------*/
@Override
public boolean equals(Object o) {
//比較引用位址
if (o == this) {
return true;
}
//類型不同
if (!(o instanceof Map)) {
return false;
}
//集合不同
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;
}
@Override
public int hashCode() {
int h = 0;
Iterator<Entry<K, V>> i = entrySet().iterator();
while (i.hasNext()) {
h += i.next().hashCode();
}
return h;
}
@Override
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(' ');
}
}
@Override
protected Object clone() throws CloneNotSupportedException {
AbstractMap<?, ?> result = (AbstractMap<?, ?>) super.clone();
result.keySet = null;
result.values = null;
return result;
}
/**
* 對兩個對象進行比較
*/
private static boolean eq(Object o1, Object o2) {
return o1 == null ? o2 == null : o1.equals(o2);
}
/*---------------------------------AbstractMap對Entry的兩種實作---------------------------*/
/**
* SimpleEntry和SimpleImmutableEntry的equals()和hashcode()方法相同
*/
/**
* 可變的Entry key不可變 value可變
*/
public static class SimpleEntry<K, V> implements Entry<K, V>, java.io.Serializable {
private static final long serialVersionUID = -8499721149061103585L;
//key不可變
private final K key;
private V value;
/*--------------------兩種構造---------------------*/
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Entry<? extends K, ? extends V> entry) {
key = entry.getKey();
value = entry.getValue();
}
/**
* 重寫Map.Entry方法
*/
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public V setValue(V value) {
V oldValue = this.value;
this.value = value;
return oldValue;
}
//隻比較key 和value
@Override
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());
}
@Override
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
}
@Override
public String toString() {
return key + "=" + value;
}
}
/**
* 不可變的Entry key不可變 value不可變
*/
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) {
key = entry.getKey();
value = entry.getValue();
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
/**
* value不可變 是以調用此方法報異常
*/
@Override
public V setValue(V value) {
throw new UnsupportedOperationException();
}
//隻比較key和value
@Override
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());
}
@Override
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
}
@Override
public String toString() {
return key + "=" + value;
}
}
}