JAVA8新特性：Lambda 表达式使用方法（为什么慢探索）

目录

​​demo​​

​​为什么慢？​​

Lambda表达式简洁，但是性能不佳。

demo

package com.nio4444.demo.java8;

import java.util.ArrayList;
import java.util.List;

public class LambdaDemo {
    public static void main(String[] args) {
        System.out.println("--1-------");
        test1();

        System.out.println();
        System.out.println("--2-------");
        test2();

        System.out.println();
        System.out.println("--3-------");
        test3();
    }

    public static void  test1(){
        long stime0 = System.currentTimeMillis() ;
        List list = new ArrayList();
        for (int i = 0; i < 10000000; i++) {
            list.add(i);
        }
        long stime = System.currentTimeMillis() ;
        System.out.println("" + (stime-stime0));

        for (int i = 0; i < list.size(); i++) { }
        long stime1 = System.currentTimeMillis() ;
        System.out.println("普通耗时：" + (stime1-stime));


        for (Object o : list) {
//            System.out.println(o.toString());
        }
        long etime = System.currentTimeMillis() ;
        System.out.println("foreach耗时：" + (etime-stime1));

        list.forEach( obj -> {
//            System.out.println(obj.toString());
        });
        long etime2 = System.currentTimeMillis() ;
        System.out.println("lambda耗时：" + (etime2-etime));
    }

    public static void  test2(){
        long stime0 = System.currentTimeMillis() ;
        List list = new ArrayList();
        for (int i = 0; i < 10000000; i++) {
            list.add(i);
        }
        long stime = System.currentTimeMillis() ;
        System.out.println("" + (stime-stime0));

        for (int i = 0; i < list.size(); i++) { }
        long stime1 = System.currentTimeMillis() ;
        System.out.println("普通耗时：" + (stime1-stime));


        for (Object o : list) {
//            System.out.println(o.toString());
        }
        long etime = System.currentTimeMillis() ;
        System.out.println("foreach耗时：" + (etime-stime1));

        list.forEach( obj -> {
//            System.out.println(obj.toString());
        });
        long etime2 = System.currentTimeMillis() ;
        System.out.println("lambda耗时：" + (etime2-etime));
    }

    public static void  test3(){
        long stime0 = System.currentTimeMillis() ;
        List list = new ArrayList();
        for (int i = 0; i < 10000000; i++) {
            list.add(i);
        }
        long stime = System.currentTimeMillis() ;
        System.out.println("" + (stime-stime0));

        for (int i = 0; i < list.size(); i++) { }
        long stime1 = System.currentTimeMillis() ;
        System.out.println("普通耗时：" + (stime1-stime));


        for (Object o : list) {
//            System.out.println(o.toString());
        }
        long etime = System.currentTimeMillis() ;
        System.out.println("foreach耗时：" + (etime-stime1));

        list.forEach( obj -> {
//            System.out.println(obj.toString());
        });
        long etime2 = System.currentTimeMillis() ;
        System.out.println("lambda耗时：" + (etime2-etime));
    }

}

为什么慢？

应用程序初次使用Lambda时，必须加载用于生成Lambda类的框架，因此需要更多的编译，加载的时间

使用匿名内部类来实现lambdas，编译器为每个匿名内部类生成一个新的类文件，这会影响应用程序的启动性能，加载可能是一个昂贵的操作，包括磁盘I/O和解压缩JAR文件本身。