一、成員變量
private transient Entry<K,V> header;//循環雙向鏈表的頭
二、構造方法
LinkHashMap的構造方法和HashMap的構造方法一樣,但是重寫init()方法;
@Override
void init() {
header = new Entry<>(-1, null, null, null);
//將元素的前驅和後續都指向自己,圖解
header.before = header.after = header;
}
put方法
put方法和hashMap的方法大致相似,不過重寫了addEntry方法,主要介紹addEntry方法
void addEntry(int hash, K key, V value, int bucketIndex) {
//調用父類的addEntry方法,但是重寫了createEntry方法
super.addEntry(hash, key, value, bucketIndex);
// Remove eldest entry if instructed
Entry<K,V> eldest = header.after;
if (removeEldestEntry(eldest)) {
removeEntryForKey(eldest.key);
}
}
void createEntry(int hash, K key, V value, int bucketIndex) {
HashMap.Entry<K,V> old = table[bucketIndex];
Entry<K,V> e = new Entry<>(hash, key, value, old);
table[bucketIndex] = e;
//主要看這個方法,把鏈表頭傳進去
e.addBefore(header);
size++;
}
private void addBefore(Entry<K,V> existingEntry) {
//圖解
after = existingEntry;
before = existingEntry.before;
before.after = this;
after.before = this;
}
第一次添加新的結點不是很好體現出循環雙向鏈表
第二次添加新的結點
remove方法
remove和hashMap的remove的方法很像,不過LinkedHashMap重寫了e.recordRemoval(this);這個方法
private void remove() {
//下面的代碼相當於這樣的,加個this比較好理解
//this.before.after = this.after;
//this.after.before = this.before;
//源碼
before.after = after;
after.before = before;
}
迭代器
private abstract class LinkedHashIterator<T> implements Iterator<T> {
Entry<K,V> nextEntry = header.after;
Entry<K,V> lastReturned = null;
int expectedModCount = modCount;
//如果結點不等於鏈表頭,那麼說明還有元素
public boolean hasNext() {
return nextEntry != header;
}
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
LinkedHashMap.this.remove(lastReturned.key);
lastReturned = null;
expectedModCount = modCount;
}
Entry<K,V> nextEntry() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
if (nextEntry == header)
throw new NoSuchElementException();
Entry<K,V> e = lastReturned = nextEntry;
nextEntry = e.after;
return e;
}
}