Java Collections - Collections.synchronizedMap() Examples

package com.logicbig.example.collections;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class SynchronizedMapExample {
    private static AtomicInteger counter = new AtomicInteger();

    public static void main(String... args) throws InterruptedException {
        Map<Integer, Integer> map = new HashMap<>();

        final ExecutorService e = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10000; i++) {
            e.execute(() -> map.put(counter.incrementAndGet(),
                    (int) (Math.random() * 100)));
        }
        e.shutdown();
        e.awaitTermination(1000, TimeUnit.SECONDS);
        System.out.println(map.size());//should be 10000
    }
}

package com.logicbig.example.collections;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class SynchronizedMapExample2 {
    private static AtomicInteger counter = new AtomicInteger();

    public static void main(String... args) throws InterruptedException {
        Map<Integer, Integer> m = new HashMap<>();
        Map<Integer, Integer> map = Collections.synchronizedMap(m);

        final ExecutorService e = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10000; i++) {
            e.execute(() -> map.put(counter.incrementAndGet(),
                    (int) (Math.random() * 100)));
        }
        e.shutdown();
        e.awaitTermination(1000, TimeUnit.SECONDS);
        System.out.println(map.size());//should be 10000

    }
}