java8中的stream流遍历 IT

 比较for循环、迭代器、java8Stream流遍历的不同

package cnom.test.testUtils;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Random;

public class TestCollectionsSort {

    public static void main(String[] args) throws InterruptedException {
        TestCollectionsSort test = new TestCollectionsSort();

        List<TestSortModel> list = new ArrayList<TestSortModel>();
        TestSortModel model = null;
        for (int i = 0; i < 80000; i++) {
            model = test.new TestSortModel();
            int intId = (int) (Math.random() * 100);
            model.setIntId(intId);
            model.setName("tes" + i);
            list.add(model);
        }
        //        JAVA8 使用Comparator排序
        //        list.sort(Comparator.comparing(TestSortModel::getIntId,
        //                Comparator.nullsLast(Comparator.naturalOrder())));

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

        long t1 = System.currentTimeMillis();
        for (TestSortModel tsm : list) {
            int id = tsm.getIntId();
            //            Thread.sleep(1);
            resList.add(tsm.getName());
        }
        System.out.println("增强for循环 遍历耗时：" + (System.currentTimeMillis() - t1) + ";list.size()="
                + list.size() + ";list=" + resList.toString());
        resList.clear();

        long t2 = System.currentTimeMillis();
        for (int i = 0; i < list.size(); i++) {
            int id = list.get(i).getIntId();
            //          Thread.sleep(1);
            resList.add(list.get(i).getName());
        }
        System.out.println("for循环 遍历耗时：" + (System.currentTimeMillis() - t2) + ";list.size()="
                + list.size() + ";list=" + resList.toString());
        resList.clear();

        long t3 = System.currentTimeMillis();
        Iterator<TestSortModel> it = list.iterator();
        TestSortModel tm = null;
        while (it.hasNext()) {
            tm = it.next();
            int id = tm.getIntId();
            //          Thread.sleep(1);
            resList.add(tm.getName());
        }
        System.out.println("iterator 遍历耗时：" + (System.currentTimeMillis() - t3) + ";list.size()="
                + list.size() + ";list=" + resList.toString());
        resList.clear();

        //parallerlStream遍历，适用于处理比较耗时的业务逻辑。 
        //注意：若在遍历中将元素添加到另一个list，则这个list必须是线程安全的，否则遍历过程中会出现两种情况：
        //1.这个list中的元素会有丢失的情况； 2.遍历中会抛出：ArrayIndexOutOfBoundsException
        List<TestSortModel> listt = Collections.synchronizedList(new ArrayList<TestSortModel>());
        long t4 = System.currentTimeMillis();
        list.parallelStream().forEach(tsm -> {//若是 forEachOrdered会保持原来list顺序
            int id = tsm.getIntId();
            //            listt.add(tsm);//输出的listt会有元素丢失，线程安全的list则不会
            try {
                //                Thread.sleep(1);
                resList.add(tsm.getName());//输出的resList也会有元素丢失
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        System.out
                .println("list.parallelStream().forEach() 遍历耗时：" + (System.currentTimeMillis() - t4)
                        + ";list.size()=" + resList.size() + ";list=" + resList.toString());
        resList.clear();

        long t5 = System.currentTimeMillis();
        list.stream().forEach(tsm -> {//串行执行，与for循环效率相似，代码精简
            int id = tsm.getIntId();
            try {
                //              Thread.sleep(1);
                resList.add(tsm.getName());
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        });
        System.out.println("list.stream().forEach() 遍历耗时：" + (System.currentTimeMillis() - t5)
                + ";list.size()=" + list.size() + ";list=" + resList.toString());
        resList.clear();

        long t6 = System.currentTimeMillis();
        list.forEach(tsm -> {//精简代码，与for循环效率相似
            int id = tsm.getIntId();
            try {
                //              Thread.sleep(1);
                resList.add(tsm.getName());
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        });
        System.out.println("list.forEach() 遍历耗时：" + (System.currentTimeMillis() - t6)
                + ";list.size()=" + list.size() + ";list=" + resList.toString());
        resList.clear();

        /**
         * for loop1 增强for循环 遍历耗时：80051
         * for loop2 for循环 遍历耗时：80032
         * iterator 遍历耗时：80069
         * list.parallelStream().forEach() 遍历耗时：20101  多线程环境下，执行耗时的业务逻辑时使用效率更好。
         * list.stream().forEach() 遍历耗时：80049  精简代码
         * list.forEach() 遍历耗时：80031
         */

    }

    public class TestSortModel implements Serializable {

        private static final long serialVersionUID = -890909910704287938L;

        private long longId;

        private int intId;

        private String name;

        public long getLongId() {
            return longId;
        }

        public void setLongId(long longId) {
            this.longId = longId;
        }

        public int getIntId() {
            return intId;
        }

        public void setIntId(int intId) {
            this.intId = intId;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

    }
}