Java 集合使用parallelStream 和 stream的問題

使用parallelStream代碼

public static void main(String[] args) {
        List<Integer> ids1 = Lists.newArrayList();
        List<Integer> ids2 = Lists.newArrayList();
        for(int i = 0; i < 1000; i ++){
            ids1.add(i);
        }
        ids1.parallelStream().forEach(id ->ids2.add(id));
    }

結果:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 823
	at java.util.ArrayList.add(ArrayList.java:459)
	at com.test.lambda$main$0(Md5Util.java:51)
	at com.test$$Lambda$1/399573350.accept(Unknown Source)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
	at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
	at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:902)
	at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1689)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1644)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

由於parallelStream是併發流，當使用線程不安全的list的時候可能致使數組越界，可使用線程安全的list，以下所示

List<Integer> ids2 = Collections.synchronizedList(Lists.newArrayList());

若是使用 stream()方法，單線程處理也能夠