mllee

synchronized(map){
  value = map.get(key);
}

    public V get(Object key) {
        Object k = maskNull(key);
        int hash = hash(k);
        int i = indexFor(hash, table.length);
        Entry<K,V> e = table[i]; 
        while (true) {
            if (e == null)
                return null;
            if (e.hash == hash && eq(k, e.key)) 
                return e.value;
            e = e.next;
        }
    }

    public V put(K key, V value) {
	K k = maskNull(key);
        int hash = hash(k);
        int i = indexFor(hash, table.length);

        for (Entry<K,V> e = table[i]; e != null; e = e.next) {
            if (e.hash == hash && eq(k, e.key)) {
                V oldValue = e.value;
                e.value = value;
                e.recordAccess(this);
                return oldValue;
            }
        }

        modCount++;
        addEntry(hash, k, value, i);
        return null;
    }

int i = indexFor(hash, table.length);

    /**
     * Rehashes the contents of this map into a new array with a
     * larger capacity.  This method is called automatically when the
     * number of keys in this map reaches its threshold.
     *
     * If current capacity is MAXIMUM_CAPACITY, this method does not
     * resize the map, but sets threshold to Integer.MAX_VALUE.
     * This has the effect of preventing future calls.
     *
     * @param newCapacity the new capacity, MUST be a power of two;
     *        must be greater than current capacity unless current
     *        capacity is MAXIMUM_CAPACITY (in which case value
     *        is irrelevant).
     */
    void resize(int newCapacity) {
        Entry[] oldTable = table;
        int oldCapacity = oldTable.length;
        if (oldCapacity == MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return;
        }

        Entry[] newTable = new Entry[newCapacity];
        transfer(newTable);
        table = newTable;
        threshold = (int)(newCapacity * loadFactor);
    }

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public class MapTest
{
	public static final int THREAD_COUNT = 1;
	public static final int MAP_SIZE = 1000;
	public static final int EXECUTION_MILLES = 1000;
	public static final int[] KEYS = new int[100]; 
	
	public static void main(String[] args) throws Exception
	{
		//初始化
		Random rand = new Random();
		for (int i = 0; i < KEYS.length; ++i)
		{
			KEYS[i] = rand.nextInt();
		}
				
		//创建线程
		long start = System.currentTimeMillis();
		Thread[] threads = new Thread[THREAD_COUNT];
		for (int i = 0; i < THREAD_COUNT; ++i)
		{
			//threads[i] = new UnsafeThread();
			//threads[i] = new SynchronizedThread();
			//threads[i] = new LockThread();
			//threads[i] = new ReadLockThread();
			threads[i] = new ConcurrentThread();
			threads[i].start();
		}
		
		//等待其它线程执行若干时间
		Thread.sleep(EXECUTION_MILLES);

		//统计 get 操作的次数
		long sum = 0;		
		for (int i = 0; i < THREAD_COUNT; ++i)
		{
			sum += threads[i].getClass().getDeclaredField("count").getLong(threads[i]);
		}
		long millisCost = System.currentTimeMillis() - start;
		System.out.println(sum + "(" + (millisCost) + "ms)");
		System.exit(0);
	}
	
	public static void fillMap(Map<Integer, Integer> map)
	{
		Random rand = new Random();
		
		for (int i = 0; i < MAP_SIZE; ++i)
		{
			map.put(rand.nextInt(), rand.nextInt());
		}
	}
}

class UnsafeThread extends Thread
{
	private static Map<Integer, Integer> map = new HashMap<Integer, Integer>();	
	public long count = 0;	
	
	static
	{
		MapTest.fillMap(map);
	}
	
	public void run()
	{
		for (;;)
		{
			int index = (int)(count % MapTest.KEYS.length);
			map.get(MapTest.KEYS[index]);
			++count;
		}
	}
}

class SynchronizedThread extends Thread
{
	private static Map<Integer, Integer> map = new HashMap<Integer, Integer>();	
	public long count = 0;
	
	static
	{
		MapTest.fillMap(map);
	}
	
	public void run()
	{
		for (;;)
		{
			int index = (int)(count % MapTest.KEYS.length);
			synchronized(SynchronizedThread.class)
			{
				map.get(MapTest.KEYS[index]);
			}
			++count;
		}
	}
}

class LockThread extends Thread
{
	private static Map<Integer, Integer> map = new HashMap<Integer, Integer>();	
	private static Lock lock = new ReentrantLock();
	public long count = 0;
	
	static
	{
		MapTest.fillMap(map);
	}
	
	public void run()
	{
		for (;;)
		{
			int index = (int)(count % MapTest.KEYS.length);
			lock.lock();
			map.get(MapTest.KEYS[index]);
			lock.unlock();
			++count;
		}
	}
}

class ReadLockThread extends Thread
{
	private static Map<Integer, Integer> map = new HashMap<Integer, Integer>();	
	private static Lock lock = new ReentrantReadWriteLock().readLock();
	public long count = 0;
	
	static
	{
		MapTest.fillMap(map);
	}
	
	public void run()
	{
		for (;;)
		{
			int index = (int)(count % MapTest.KEYS.length);
			lock.lock();
			map.get(MapTest.KEYS[index]);
			lock.unlock();
			++count;
		}
	}
}

class ConcurrentThread extends Thread
{
	private static Map<Integer, Integer> map = new ConcurrentHashMap<Integer, Integer>();	
	public long count = 0;
	
	static
	{
		MapTest.fillMap(map);
	}
	
	public void run()
	{
		for (;;)
		{
			int index = (int)(count % MapTest.KEYS.length);
			map.get(MapTest.KEYS[index]);
			++count;
		}
	}
}