Java中for循环效率比较

先说结论：

对于遍历一个1千万条数据的arrayList，fori循环最快，iterator其次，foreach再其次，forStream最慢。

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测试代码

public class ForSpeedTest {//    private static final long FOR_COUNT = 10000_0000;private static final long FOR_COUNT = 1000_0000;
//    private static final long FOR_COUNT = 100_0000;
//    private static final long FOR_COUNT = 10_0000;
//    private static final long FOR_COUNT = 1_0000;
//    private static final long FOR_COUNT = 100;private static List<String> arrayList = new ArrayList<>();static {//数据准备for (int i = 0; i < FOR_COUNT; i++) {arrayList.add("abc" + i);}  }public static void main(String[] args) throws Exception{Thread.sleep(1000);StopWatch stopWatch = new StopWatch();stopWatch.start("forI");forI();stopWatch.stop();stopWatch.start("forEach");forEeach();stopWatch.stop();stopWatch.start("forStream");forStream();stopWatch.stop();stopWatch.start("forI2");forI2();stopWatch.stop();stopWatch.start("iterator");forIterator();stopWatch.stop();System.out.println(stopWatch.prettyPrint());}private static void forI() {long size = arrayList.size();for (int i = 0; i < size; i++) {}}private static void forEeach() {for (String s : arrayList) {}}private static void forStream() {arrayList.forEach(x -> {});}private static void forI2() {for (int i = 0; i < arrayList.size(); i++) {}}private static void forIterator() {Iterator<String> iterator = arrayList.iterator();while(iterator.hasNext()){iterator.next();}}}