Bench.java

import java.util.*;

public class Bench {
    public static final int _keyRange = 100;
    public static final int _threadCount = 300;
    public static final int _repeat = 100000;

    //--------------------------------------------------------------------------------

    public static void main(String[] args) throws Exception {
        final long start = System.currentTimeMillis();
        final Map map = new HashMap();
        Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
            public void run() {
                System.out.println(System.currentTimeMillis() - start);
                System.out.println(map);
            }
        }));
        for (int i = 0; i < _threadCount; ++i) {
            new Thread(new Runnable() {
                public void run() {
                    for (int k = 0; k < _repeat; ++k) {
                        Random random = new Random();
                        String key = "key" + random.nextInt(_keyRange);
                        synchronized(map) {
                            Integer value = (Integer) map.get(key);
                            if (value != null) {
                                int oldValue = value.intValue();
                                map.put(key, new Integer(oldValue + 1));
                            } else {
                                map.put(key, new Integer(1));
                            }
                        }
                    }
                }
            }).start();
        }
    }

    //--------------------------------------------------------------------------------

}

cf. https://github.com/lagenorhynque/bench