集合容器类线程不安全demo,以及解决方案;

  List<String> list = new ArrayList<>();

        for (int i = 1; i <= 22; i++){

            new Thread(new Runnable() {
                @Override
                public void run() {
                    list.add(UUID.randomUUID().toString().substring(0,8));
                    System.out.println(list);
                }
            },String.valueOf(i)).start();
        }

如图多个线程操作同一个arraylist 会报并发修改异常;

以下说解决方案;

1.List list =new Vector();

集合容器类线程不安全demo,以及解决方案;

vector的add是同步方法,可以解决一致性问题,但是并发性会下降,所以一般不用vector;

3.解决方案2,Collections工具类中提供了synchronizedList,synchronizedMap 等方法,可以创建并发环境下的容器;

  List<String> list2 = Collections.synchronizedList(new ArrayList<>());

        for (int i = 1; i <= 22; i++){

            new Thread(new Runnable() {
                @Override
                public void run() {
                    list2.add(UUID.randomUUID().toString().substring(0,8));
                    System.out.println(list2);
                }
            },String.valueOf(i)).start();
        }


[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5]
[97094e8f, f0ed1777, 09a000a9, b0139b6a]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61]
[97094e8f, f0ed1777, 09a000a9]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45, 01c9f7c2]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45, 01c9f7c2, 657aeb20]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45, 01c9f7c2, 657aeb20, a9835bcf]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45, 01c9f7c2, 657aeb20, a9835bcf, b5c384b5]
[97094e8f, f0ed1777, 09a000a9, b0139b6a, 1ebcee80, 77c7bbd1, 78c0735a, cb3f9ae1, da97c567, d2f3b789, 1ae70cd5, 7c703f61, dc1244bd, c208cb1f, d2528c4c, 0ca0cf66, 21124d45, 01c9f7c2, 657aeb20, a9835bcf, b5c384b5, b90ee122]

代码执行正确,不会报错;

4.还有另一种JUC包提供的解决方案

java.util.concurrent
类 CopyOnWriteArrayList<E>;

集合容器类线程不安全demo,以及解决方案;

demo

集合容器类线程不安全demo,以及解决方案;

举一反三,其他类型集合并发的问题示例,以及解决的方法

 private static void mapNotSafe() {
//        HashMap<String, String> map = new HashMap<>(); 有问题
            
//        Map<String, String> objectObjectMap = Collections.synchronizedMap(new HashMap<>());  解决

        //解决
        ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();

        for (int i = 0; i < 55; i++) {

            new Thread(new Runnable() {

                public void run() {

                    map.put(UUID.randomUUID().toString().substring(0, 8),UUID.randomUUID().toString().substring(0, 8));
                    System.out.println(map);
                }

            },String.valueOf(i)).start();

        }
    }

    private static void setNotSafe() {
//                HashSet<String> set = new HashSet<>();
        Set<String> set = new CopyOnWriteArraySet<String>();
        for (int i = 1; i <= 25; i++) {

            new Thread(new Runnable() {
                @Override
                public void run() {
                    set.add(UUID.randomUUID().toString().substring(0, 8));
                    System.out.println(set);
                }
            }, String.valueOf(i)).start();
        }
    }

    private static void listNotSafe() {
        //        List<String> list = Arrays.asList("a", "b", "c");

//        list.forEach(System.out::println);

        List<String> list = new ArrayList<>();
//        List<String> list = Collections.synchronizedList(new ArrayList<>());

        for (int i = 1; i <= 22; i++) {

            new Thread(new Runnable() {
                @Override
                public void run() {
                    list.add(UUID.randomUUID().toString().substring(0, 8));
                    System.out.println(list);
                }
            }, String.valueOf(i)).start();
        }
    }

集合容器类线程不安全demo,以及解决方案;

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