Hashtable和HashMap引发的血案

6vcn

public class Hashtable<K,V>extends Dictionary<K,V>implements Map<K,V>, Cloneable, java.io.Serializable {…}public class HashMap<K,V>extends AbstractMap<K,V>implements Map<K,V>, Cloneable, Serializable {…}

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public synchronized V put(K key, V value) {// Make sure the value is not nullif (value == null) {throw new NullPointerException();}// Makes sure the key is not already in the hashtable.Entry tab[] = table;int hash = key.hashCode();int index = (hash & 0x7FFFFFFF) % tab.length;//…}??

import java.util.HashMap;import java.util.Map;import java.util.Map.Entry;public class TestCase {public static void main(String[] args) {Map<Integer,String> hashMap = new HashMap<Integer,String>();hashMap.put(0, null);hashMap.put(1, "one");hashMap.put(2, "two");hashMap.put(null, "null");for(Entry<Integer, String> e : hashMap.entrySet()) {System.out.println("Key: " + e.getKey() + " -- Value: " + e.getValue());}System.out.println(hashMap.get(0));System.out.println(hashMap.get(4));System.out.println("Contains key 0 ? :" + hashMap.containsKey(0));System.out.println("Contains key 4 ? :" + hashMap.containsKey(4));System.out.println("Contains value null ? :" + hashMap.containsValue(null));}}?

结果：

Key: null -- Value: nullKey: 0 -- Value: nullKey: 1 -- Value: oneKey: 2 -- Value: twonullnullContains key 0 ? :trueContains key 4 ? :falseContains value null ? :true

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public synchronized V put(K key, V value) {// Make sure the value is not nullif (value == null) {throw new NullPointerException();}// Makes sure the key is not already in the hashtable.Entry tab[] = table;int hash = key.hashCode();//hashcodeint index = (hash & 0x7FFFFFFF) % tab.length;//…}?

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public V put(K key, V value) {if (key == null)return putForNullKey(value);int hash = hash(key.hashCode());//hashcodeint i = indexFor(hash, table.length);//…}static int hash(int h) {h ^= (h >>> 20) ^ (h >>> 12);return h ^ (h >>> 7) ^ (h >>> 4);}

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/*** The default initial capacity - MUST be a power of two.*/static final int DEFAULT_INITIAL_CAPACITY = 16;/*** The load factor used when none specified in constructor.*/static final float DEFAULT_LOAD_FACTOR = 0.75f;?

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public Hashtable() {this(11, 0.75f);}protected void rehash() {int oldCapacity = table.length;Entry[] oldMap = table;int newCapacity = oldCapacity * 2 + 1;//…}?

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public HashMap(Map<? extends K, ? extends V> m) {this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);putAllForCreate(m);}?

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public Hashtable(Map<? extends K, ? extends V> t) {this(Math.max(2*t.size(), 11), 0.75f);putAll(t);}?

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