HashTable源码

 1. 为什么无法创建更大的数组？

Attempts to allocate larger arrays may result in OutOfMemoryError

如果数组长度过大，可能出现的两种错误

OutOfMemoryError: Java heap space  堆区内存不足（这个可以通过设置JVM参数 -Xmx 来指定）。

OutOfMemoryError: Requested array size exceeds VM limit  超过了JVM虚拟机的最大限制，我的window64就是 Integer.MAX_VALUE-1 .

  2. 为什么数组长度的最大值是Integer.MAX_VALUE - 8

数组作为一个对象，需要一定的内存存储对象头信息，对象头信息最大占用内存不可超过8字节。

HashMap的方法是非同步的，若要在多线程下使用HashMap，需要我们额外的进行同步处理。对HashMap处理可以使用Collections类提供的synchronizedMap静态方法，或者直接使用JDK5.0之后提供的java.util.concurrent包里的ConcurrentHashMap类。

HashTable几乎所有方法都是同步的，前面都加了synchronized关键字，它支持多线程。

HashTable几乎所有方法都是同步的，前面都加了synchronized关键字，它支持多线程。

HashMap的key和value都可以为null。

HashTable的key和value都不可以为null。

HashMap只支持Iterator遍历。

HashTable支持Iterator和Enumeration两种方式遍历。

HashMap的默认容量是16,，扩容时，每次将容量变为原来的2倍；

HashTable的默认容量是11，扩容时，每次将容量变为原来的2倍+1。

HashMap添加元素时，是使用自定义的哈希算法；

HashTable是直接采用key的hashCode()。

 

public class testhashtable {
    @SuppressWarnings({ "unused", "unchecked", "rawtypes" })
    public static void main(String[] args) {
        Hashtable1<Integer, Integer> numbers = new Hashtable1<Integer, Integer>();
        numbers.put(1, 1);
        numbers.put(12, 12);
        numbers.put(23, 23);
        numbers.put(2, 2);
        numbers.put(3, 3);
        
        Hashtable1<Integer, Integer> numbers1 = (Hashtable1<Integer, Integer>) numbers.clone();

        Enumerator k1 = numbers.getEnumeration(0);//返回迭代器
        while(k1.hasNext()) {
            System.out.println(k1.next());//3 2 23 12 1
        }
        Enumerator v1 = numbers.getEnumeration(1);//返回迭代器
        while(v1.hasNext()) {
            System.out.println(v1.next());//3 2 23 12 1
        }
        Enumerator e1 = numbers.getEnumeration(2);//返回迭代器
        while(e1.hasNext()) {
            System.out.println(e1.next());//3=3 2=2 23=23 12=12 1=1
        }
        
        Enumerator k2 = (Enumerator) numbers.getIterator(0);//返回迭代器
        while(k2.hasNext()) {
            System.out.println(k2.next());//3 2 23 12 1
        }
        Enumerator v2 = (Enumerator) numbers.getIterator(1);//返回迭代器
        while(v2.hasNext()) {
            System.out.println(v2.next());//3 2 23 12 1
        }
        v2.remove();
        Enumerator e2 = (Enumerator) numbers.getIterator(2);//返回迭代器
        while(e2.hasNext()) {
            System.out.println(e2.next());//3=3 2=2 23=23 12=12 1=1
        }
        
        Enumerator k3 =(Enumerator) numbers.keys();
        Enumerator v3 =(Enumerator) numbers.elements();
        Enumerator e3 =(Enumerator) numbers.keys();
        
        Set s1 = numbers.keySet1();//[3, 2, 23, 12, 1]
        int 他1 = s1.size();//5
        boolean b1 = s1.contains(1);
        boolean ss1 = s1.remove(1);
        Iterator l1 = s1.iterator();
        while(l1.hasNext()) {
            System.out.println(l1.next());
        }
        
        Collection kkk = numbers.entrySet1();//[3=3, 2=2, 23=23, 12=12, 1=1]
        kkk.add(new Entry<>(17, 17, 17, null));
        
        Set s = numbers.keySet();//返回SynchronizedSet，都是SynchronizedSet对象的方法。
        int 他 = s.size();
        boolean b = s.contains(1);
        boolean ss = s.remove(1);
        Object[] a = s.toArray();
        boolean ml = s.isEmpty();
//        s.add(new Entry<>(4, 4, 4, null));
        Iterator l = s.iterator();
        while(l.hasNext()) {
            System.out.println(l);
        } 
        
        
        Collection v = numbers.values();
        Set e = numbers.entrySet();
        
        Collection sssv = numbers.entrySet();
        
        System.out.println(Integer.toBinaryString(-3));
        System.out.println(Integer.toBinaryString(-3 & 0x7FFFFFFF));
        System.out.println(-3 & 0x7FFFFFFF);//2147483645=2^31-3
        
        /*int i = 2147483648;// out of range ,2^31
        int j = 2147483647; //2147483647 = 01111111 11111111 11111111 11111111 = 2^31(位)-1
        int k =-2147483649;//  out of range 
        int l =-2147483648;//10000000 00000000 00000000 00000000,-2^31,  */
    }
}

 

package map;

public class Hashtable1<K,V> extends Dictionary<K,V> implements Map1<K,V>, Cloneable, java.io.Serializable {
    public transient Entry<?,?>[] table;
    public transient int count;//链表节点个数
    public int threshold;//阈值capacity * loadFactor
    public float loadFactor;
    public transient int modCount = 0;
    public static final long serialVersionUID = 1421746759512286392L;

    public Hashtable1(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity);
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal Load: "+loadFactor);
        if (initialCapacity==0)
            initialCapacity = 1;
        this.loadFactor = loadFactor;
        table = new Entry<?,?>[initialCapacity];
        threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
    }
    public Hashtable1(int initialCapacity) {
        this(initialCapacity, 0.75f);
    }
    public Hashtable1() {
        this(11, 0.75f);//默认初始化11个，
    }
    public Hashtable1(Map1<? extends K, ? extends V> t) {
        this(Math.max(2*t.size(), 11), 0.75f);
        putAll(t);
    }
    public synchronized int size() {//线程安全
        return count;
    }
    public synchronized boolean isEmpty() {//线程安全
        return count == 0;
    }
    //线程安全
    public synchronized Enumeration<K> keys() {
        return this.<K>getEnumeration(KEYS);//0
    }
    //线程安全
    public synchronized Enumeration<V> elements() {
        return this.<V>getEnumeration(VALUES);//1
    }
    //线程安全
    public synchronized boolean contains(Object value) {
        if (value == null) {
            throw new NullPointerException();
        }
        Entry<?,?> tab[] = table;
        for (int i = tab.length ; i-- > 0 ;) {
            for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) {
                if (e.value.equals(value)) {//数组加链表
                    return true;
                }
            }
        }
        return false;
    }
    public boolean containsValue(Object value) {
        return contains(value);
    }
    //线程安全
    public synchronized boolean containsKey(Object key) {
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;//hash为负数：2^31 -|hash|。
        for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                return true;
            }
        }
        return false;
    }
    //线程安全
    public synchronized V get(Object key) {
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                return (V)e.value;
            }
        }
        return null;
    }
    //虚拟机给数组有头信息，8*4个字节=32字节。
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
    //线程安全
    protected void rehash() {
        int oldCapacity = table.length;
        Entry<?,?>[] oldMap = table;
        int newCapacity = (oldCapacity << 1) + 1;//2*oldCapacity+1
        if (newCapacity - MAX_ARRAY_SIZE > 0) {
            if (oldCapacity == MAX_ARRAY_SIZE)
                return;
            newCapacity = MAX_ARRAY_SIZE;
        }
        Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
        modCount++;//遍历时候不能进行rehash操作
        threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
        table = newMap;
        for (int i = oldCapacity ; i-- > 0 ;) {//遍历数组
            for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {//遍历链表
                Entry<K,V> e = old;
                old = old.next;
                int index = (e.hash & 0x7FFFFFFF) % newCapacity;
                e.next = (Entry<K,V>)newMap[index];//放在最前面
                newMap[index] = e;
            }
        }
    }
    private void addEntry(int hash, K key, V value, int index) {
        modCount++;
        Entry<?,?> tab[] = table;
        if (count >= threshold) {
            rehash();
            tab = table;
            hash = key.hashCode();
            index = (hash & 0x7FFFFFFF) % tab.length;
        }
        Entry<K,V> e = (Entry<K,V>) tab[index];
        tab[index] = new Entry<>(hash, key, value, e);//添加到最前面
        count++;
    }
    //线程安全
    public synchronized V put(K key, V value) {
        if (value == null) {
            throw new NullPointerException();
        }
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        Entry<K,V> entry = (Entry<K,V>)tab[index];
        for(; entry != null ; entry = entry.next) {//遍历链表
            if ((entry.hash == hash) && entry.key.equals(key)) {
                V old = entry.value;
                entry.value = value;
                return old;
            }
        }
        addEntry(hash, key, value, index);
        return null;
    }
    //线程安全
    public synchronized V remove(Object key) {
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                modCount++;
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    tab[index] = e.next;//第一个元素
                }
                count--;
                V oldValue = e.value;
                e.value = null;
                return oldValue;
            }
        }
        return null;
    }
    //线程安全
    public synchronized void putAll(Map1<? extends K, ? extends V> t) {
        for (Map1.Entry<? extends K, ? extends V> e : t.entrySet())
            put(e.getKey(), e.getValue());
    }
    //线程安全
    public synchronized void clear() {
        Entry<?,?> tab[] = table;
        modCount++;
        for (int index = tab.length; --index >= 0; )
            tab[index] = null;
        count = 0;
    }
    //线程安全
    public synchronized Object clone() {
        try {
            Hashtable1<?,?> t = (Hashtable1<?,?>)super.clone();
            Hashtable1<?,?> tt = this;//2者的地址都是一模一样的。new的地址不一样。
            t.table = new Entry<?,?>[table.length];
            for (int i = table.length ; i-- > 0 ; ) {//地址不一样了
                t.table[i] = (table[i] != null) ? (Entry<?,?>) table[i].clone() : null;
            }
            t.keySet = null;
            t.entrySet = null;
            t.values = null;
            t.modCount = 0;
            return t;
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }
    //线程安全
    public synchronized String toString() {
        int max = size() - 1;
        if (max == -1)
            return "{}";
        StringBuilder sb = new StringBuilder();
        Iterator<Map1.Entry<K,V>> it = entrySet().iterator();
        sb.append('{');
        for (int i = 0; ; i++) {
            Map1.Entry<K,V> e = it.next();
            K key = e.getKey();
            V value = e.getValue();
            sb.append(key   == this ? "(this Map)" : key.toString());
            sb.append('=');
            sb.append(value == this ? "(this Map)" : value.toString());
            if (i == max)
                return sb.append('}').toString();
            sb.append(", ");
        }
    }

    public <T> Enumerator<T> getEnumeration(int type) {//0是keys，1是values，2是Entry。
        if (count == 0) {
            return (Hashtable1<K, V>.Enumerator<T>) Collections1.emptyEnumeration();
        } else {
            return new Enumerator<>(type, false);//false返回枚举器
        }
    }

    public <T> Iterator<T> getIterator(int type) {//0是keys，1是values，2是Entry。
        if (count == 0) {
            return Collections1.emptyIterator();
        } else {
            return new Enumerator<>(type, true);//true返回迭代器Iterator
        }
    }

    private transient volatile Set<K> keySet;
    private transient volatile Set<Map1.Entry<K,V>> entrySet;
    private transient volatile Collection<V> values;

    public Set<K> keySet() {
        if (keySet == null)                        //内部KeySet对象，整个hashtable                
            keySet = Collections1.synchronizedSet(new KeySet(), this);
        return keySet;
    }
    public Set<K> keySet1() {
        if (keySet == null)
            keySet =  new KeySet() ;//[888, 888, 888, 888, 888],是根据new KeySet()的iterator()返回的Iterator对象的hasNext()和next()方法确定值的。
        return keySet;
    }

    private class KeySet extends AbstractSet<K> {
        public Iterator<K> iterator() {
            return getIterator(KEYS);
        }
        public int size() {
            return count;//外部属性。外部类的属性不能通过点来访问，只能通过方法来访问。
        }
        public boolean contains(Object o) {
            return containsKey(o);//外部方法
        }
        public boolean remove(Object o) {
            return Hashtable1.this.remove(o) != null;//外部方法
        }
        public void clear() {
            Hashtable1.this.clear();//外部方法
        }
    }

    public Set<Map1.Entry<K,V>> entrySet() {
        if (entrySet==null)
            entrySet = Collections1.synchronizedSet(new EntrySet(), this);
        return entrySet;
    }
    public Set<Map1.Entry<K,V>> entrySet1() {
        if (entrySet==null)
            entrySet =  new EntrySet() ;//[3=3, 2=2, 23=23, 12=12, 1=1]
        return entrySet;
    }

    private class EntrySet extends AbstractSet<Map1.Entry<K,V>> {
        public Iterator<Map1.Entry<K,V>> iterator() {
            return getIterator(ENTRIES);
        }
        public boolean add(Map1.Entry<K,V> o) {
            return super.add(o);//不能添加，报错。
        }
        public boolean contains(Object o) {
            if (!(o instanceof Map1.Entry))
                return false;
            Map1.Entry<?,?> entry = (Map1.Entry<?,?>)o;
            Object key = entry.getKey();
            Entry<?,?>[] tab = table;
            int hash = key.hashCode();
            int index = (hash & 0x7FFFFFFF) % tab.length;
            for (Entry<?,?> e = tab[index]; e != null; e = e.next)
                if (e.hash==hash && e.equals(entry))
                    return true;
            return false;
        }
        public boolean remove(Object o) {
            if (!(o instanceof Map1.Entry))
                return false;
            Map1.Entry<?,?> entry = (Map1.Entry<?,?>) o;
            Object key = entry.getKey();
            Entry<?,?>[] tab = table;
            int hash = key.hashCode();
            int index = (hash & 0x7FFFFFFF) % tab.length;

            @SuppressWarnings("unchecked")
            Entry<K,V> e = (Entry<K,V>)tab[index];
            for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
                if (e.hash==hash && e.equals(entry)) {
                    modCount++;
                    if (prev != null)
                        prev.next = e.next;
                    else
                        tab[index] = e.next;
                    count--;
                    e.value = null;
                    return true;
                }
            }
            return false;
        }
        public int size() {
            return count;
        }
        public void clear() {
            Hashtable1.this.clear();
        }
    }

    public Collection<V> values() {
        if (values==null)
            values = Collections1.synchronizedCollection(new ValueCollection(),this);
        return values;
    }

    private class ValueCollection extends AbstractCollection<V> {
        public Iterator<V> iterator() {
            return getIterator(VALUES);
        }
        public int size() {
            return count;
        }
        public boolean contains(Object o) {
            return containsValue(o);
        }
        public void clear() {
            Hashtable1.this.clear();
        }
    }

    public synchronized boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof Map))
            return false;
        Map1<?,?> t = (Map1<?,?>) o;
        if (t.size() != size())//大小相等
            return false;
        try {
            Iterator<Map1.Entry<K,V>> i = entrySet().iterator();
            while (i.hasNext()) {
                Map1.Entry<K,V> e = i.next();
                K key = e.getKey();
                V value = e.getValue();
                if (value == null) {
                    if (!(t.get(key)==null && t.containsKey(key)))
                        return false;
                } else {
                    if (!value.equals(t.get(key)))
                        return false;
                }
            }
        } catch (ClassCastException unused)   {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }
        return true;
    }

    public synchronized int hashCode() {
        int h = 0;
        if (count == 0 || loadFactor < 0)
            return h;  // 返回 0
        loadFactor = -loadFactor;  // Mark hashCode computation in progress
        Entry<?,?>[] tab = table;
        for (Entry<?,?> entry : tab) {
            while (entry != null) {
                h += entry.hashCode();
                entry = entry.next;
            }
        }
        loadFactor = -loadFactor;  // Mark hashCode computation complete
        return h;
    }

    @Override
    public synchronized V getOrDefault(Object key, V defaultValue) {
        V result = get(key);
        return (null == result) ? defaultValue : result;
    }

    @SuppressWarnings("unchecked")
    @Override
    public synchronized void forEach(BiConsumer<? super K, ? super V> action) {
        Objects.requireNonNull(action);      
        final int expectedModCount = modCount;
        Entry<?, ?>[] tab = table;
        for (Entry<?, ?> entry : tab) {//全部遍历
            while (entry != null) {
                action.accept((K)entry.key, (V)entry.value);
                entry = entry.next;
                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public synchronized void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
        Objects.requireNonNull(function);      
        final int expectedModCount = modCount;
        Entry<K, V>[] tab = (Entry<K, V>[])table;
        for (Entry<K, V> entry : tab) {
            while (entry != null) {
                entry.value = Objects.requireNonNull(function.apply(entry.key, entry.value));
                entry = entry.next;
                if (expectedModCount != modCount) {
                    throw new ConcurrentModificationException();
                }
            }
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public synchronized V putIfAbsent(K key, V value) {
        Objects.requireNonNull(value);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        Entry<K,V> entry = (Entry<K,V>)tab[index];
        for (; entry != null; entry = entry.next) {
            if ((entry.hash == hash) && entry.key.equals(key)) {
                V old = entry.value;
                if (old == null) {
                    entry.value = value;
                }
                return old;
            }
        }
        addEntry(hash, key, value, index);
        return null;
    }

    @Override
    public synchronized boolean remove(Object key, Object value) {
        Objects.requireNonNull(value);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
                modCount++;
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    tab[index] = e.next;
                }
                count--;
                e.value = null;
                return true;
            }
        }
        return false;
    }

    @Override
    public synchronized boolean replace(K key, V oldValue, V newValue) {
        Objects.requireNonNull(oldValue);
        Objects.requireNonNull(newValue);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                if (e.value.equals(oldValue)) {
                    e.value = newValue;
                    return true;
                } else {
                    return false;
                }
            }
        }
        return false;
    }

    @Override
    public synchronized V replace(K key, V value) {
        Objects.requireNonNull(value);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if ((e.hash == hash) && e.key.equals(key)) {
                V oldValue = e.value;
                e.value = value;
                return oldValue;
            }
        }
        return null;
    }

    @Override
    public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (; e != null; e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                return e.value;
            }
        }
        V newValue = mappingFunction.apply(key);
        if (newValue != null) {
            addEntry(hash, key, newValue, index);
        }
        return newValue;
    }

    @Override
    public synchronized V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                V newValue = remappingFunction.apply(key, e.value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }
        return null;
    }

    @Override
    public synchronized V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && Objects.equals(e.key, key)) {
                V newValue = remappingFunction.apply(key, e.value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }
        V newValue = remappingFunction.apply(key, null);
        if (newValue != null) {
            addEntry(hash, key, newValue, index);
        }
        return newValue;
    }

    @Override
    public synchronized V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
        Entry<?,?> tab[] = table;
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % tab.length;
        @SuppressWarnings("unchecked")
        Entry<K,V> e = (Entry<K,V>)tab[index];
        for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash && e.key.equals(key)) {
                V newValue = remappingFunction.apply(e.value, value);
                if (newValue == null) {
                    modCount++;
                    if (prev != null) {
                        prev.next = e.next;
                    } else {
                        tab[index] = e.next;
                    }
                    count--;
                } else {
                    e.value = newValue;
                }
                return newValue;
            }
        }
        if (value != null) {
            addEntry(hash, key, value, index);
        }
        return value;
    }

    //链表元素
    public static class Entry<K,V> implements Map1.Entry<K,V> {
        public final int hash;
        public final K key;
        public V value;
        public Entry<K,V> next;
        public Entry(int hash, K key, V value, Entry<K,V> next) {
            this.hash = hash;
            this.key =  key;
            this.value = value;
            this.next = next;
        }
        @SuppressWarnings("unchecked")
        public Object clone() {//super.clone()地址是一样的，new就不一样了。
            return new Entry<>(hash, key, value, (next==null ? null : (Entry<K,V>) next.clone()));
        }
        public K getKey() {
            return key;
        }
        public V getValue() {
            return value;
        }
        public V setValue(V value) {
            if (value == null)
                throw new NullPointerException();
            V oldValue = this.value;
            this.value = value;
            return oldValue;
        }
        public boolean equals(Object o) {
            if (!(o instanceof Map1.Entry))
                return false;
            Map1.Entry<?,?> e = (Map1.Entry<?,?>)o;
            return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
               (value==null ? e.getValue()==null : value.equals(e.getValue()));
        }
        public int hashCode() {
            return hash ^ Objects.hashCode(value);
        }
        public String toString() {
            return key.toString()+"="+value.toString();
        }
    }

    private static final int KEYS = 0;
    private static final int VALUES = 1;
    private static final int ENTRIES = 2;

    public class Enumerator<T> implements Enumeration<T>, Iterator<T> {
        Entry<?,?>[] table = Hashtable1.this.table;
        int index = table.length;//从后往前
        Entry<?,?> entry;//next
        Entry<?,?> lastReturned;//prev
        int type;//0是keys，1是values，2是Entry。

        //true是迭代，false是枚举
        boolean iterator;

        protected int expectedModCount = modCount;

        Enumerator(int type, boolean iterator) {//6种组合
            this.type = type;//0是keys，1是values，2是Entry。
            this.iterator = iterator;//true返回迭代器Iterator，false返回枚举器
        }

        public boolean hasMoreElements() {
            Entry<?,?> e = entry;//初始化entry=null
            int i = index;//index=length
            Entry<?,?>[] t = table;
            /* 使用局部变量加快循环迭代 */
            while (e == null && i > 0) {
                e = t[--i];//从数组从后往前找，找到第一个不为null的，初始化。到了链表末尾查找下一个不为null的。
            }
            entry = e;//下次要返回的
            index = i;//下次要返回的索引
            return e != null;
        }

        @SuppressWarnings("unchecked")
        public T nextElement() {
            Entry<?,?> et = entry;
            int i = index;
            Entry<?,?>[] t = table;
            /* 使用局部变量加快循环迭代 */
            while (et == null && i > 0) {
                et = t[--i];//进不来
            }
            entry = et;
            index = i;
            if (et != null) {
                Entry<?,?> e = lastReturned = entry;
                entry = e.next;//链表下一个
                return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
            }
            throw new NoSuchElementException("Hashtable Enumerator");
        }

        int m = 5;
        public boolean hasNext() {
            return /* m-->0; */hasMoreElements();
        }

        public T next() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            return /* (T) new Integer(888); */nextElement();
        }

        public void remove() {
            if (!iterator)//枚举不能删除，迭代器可以删除。
                throw new UnsupportedOperationException();
            if (lastReturned == null)
                throw new IllegalStateException("Hashtable Enumerator");
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();

            synchronized(Hashtable1.this) {
                Entry<?,?>[] tab = Hashtable1.this.table;
                int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;//删除lastReturned节点

                @SuppressWarnings("unchecked")
                Entry<K,V> e = (Entry<K,V>)tab[index];
                for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
                    if (e == lastReturned) {
                        modCount++;
                        expectedModCount++;
                        if (prev == null)
                            tab[index] = e.next;
                        else
                            prev.next = e.next;
                        count--;
                        lastReturned = null;
                        return;
                    }
                }
                throw new ConcurrentModificationException();
            }
        }
    }
}