java-线程池,Lambda表达式,File类

线程池使用场景:

当并发的数量很多,并且每一个线程都是执行一个很短的任务就结束了.这样子频繁创建线程就会大大降低系统的效率,因为频繁创建和销毁都需要时间.这时我们就需要线程池了,线程池可以使得一个线程复用

线程池代码实现

线程池的使用步骤

创建Runnable接口的实现类RunnableImpl

public class RunnableImpl implements Runnable {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"创建了一个新的线程");
    }
}

主程序

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

    public class t1 {
        public static void main(String[] args){
            ExecutorService es = Executors.newFixedThreadPool(2);
            es.submit(new RunnableImpl());//pool-1-thread-1创建了一个新的线程
            es.submit(new RunnableImpl());//pool-1-thread-2创建了一个新的线程
            es.submit(new RunnableImpl());//pool-1-thread-1创建了一个新的线程
        }

Lambda表达式

函数式编程与面向对象编程区别

面向对象思想:做一件事,通过创建多个相关联的类,每个类设置自身的方法调用对象方法,完成事情
函数式编程思想:y=x+a-b+c 传入x参数返回y参数,通过传入参数返回结果完成事情

    public class t1 {
        public static void main(String[] args) {
            //使用匿名内部类
            new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName()+"创建了一个新的线程");
                }
            }).start();


            //使用lambda表达式
            new Thread(()->{
        System.out.println(Thread.currentThread().getName()+"创建了一个新的线程");
            }

            ).start();
        }
}

Lambda表达式格式说明

使用场景:

Lambda表达式作用就是简化匿名内部类把内部类简化为一个()->

使用前提

案例:使用Lambda标准格式(无参数无返回)

创建一个Cook接口

public interface Cook {
    void makeFood();

主程序

public class t1 {
    public static void main(String[] args) {
        //调用invokeCook,参数是Cokk接口,传递Cokk接口匿名内部类对象
        invokeCook(new Cook() {
            @Override
            public void makeFood() {
                System.out.println("吃饭了");
            }
        });
        //lambda形式
        invokeCook(()->{
            System.out.println("在吃一回");
        });
    }
    private static void invokeCook(Cook cook){
        cook.makeFood();
    }
}

案例:使用Lambda标准格式(有参数,有返回)

创建Person类

public class Person {
    private String name;
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }


    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }


}

主程序

import java.util.Arrays;

public class t1 {
    public static void main(String[] args) {
        Person[] arr={
                new Person("柳岩",18),
                new Person("范冰冰",20),
                new Person("季童童",35),
        };
        Arrays.sort(arr,(Person o1,Person o2)->{
            return o1.getAge()-o2.getAge();
        });
        for (Person person : arr) {
            System.out.println(person);
        }
    }

}

创建Calculator接口类

public interface Calculator {
        abstract int calc(int a, int b);
}

主程序

public class t1 {
    public static void main(String[] args) {
        invokeCalc(120,130,(int a,int b)->{
            return a+b;
        });
    }
    private static void invokeCalc(int a,int b,Calculator calulator){
        int result = calulator.calc(a,b);
        System.out.println("结果是:"+result);
    }

}

Lambda省略模式

public class t1 {
    public static void main(String[] args) {
        //省略版lambda形式1:省略掉{}
        new Thread(()-> System.out.println(Thread.currentThread().getName()));
        
        //省略版lambda形式2:省略掉参数类型定义,{},return语句
        Arrays.sort(arr,(o1,o2)->o1.getAge()-o2.getAge);

File类的概述

File类的静态成员变量

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        String pathSeparator = File.pathSeparator;
        System.out.println(pathSeparator);//路径分隔符;

        String separator = File.separator;//文件名称分隔符\
        System.out.println(separator);//windows:反斜杠\ linux:正斜杠/
    }
}

绝对路径和相对路径

File类的构造方法

public class t1 {
    public static void main(String[] args) {
        show02();
    }

    private static void show02() {
        File file = new File("D:\\BaiduNetdiskDownload");
        System.out.println(file);//D:\BaiduNetdiskDownload
    }
}

public class t1 {
    public static void main(String[] args) {
        show02("c:\\","a.txt");
    }

    private static void show02(String parent,String child) {
        File file = new File(parent,child);
        System.out.println(file);//c:\a.txt
    }  
}

父路径可不是字符串了而是File类型

public class t1 {
    public static void main(String[] args) {
        show02();
    }

    private static void show02() {
        File parent = new File("c:\\");
        File file = new File(parent, "hello.java");
        System.out.println(file);//c:\hello.java
    }
}

File类获取功能的方法

getNmae 方法可以使File类型转换成String类型

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    
    private static void show01() {
        File file = new File("D:\\BaiduNetdiskDownload\\a.txt");
        String absolutePath = file.getAbsolutePath();
        System.out.println(absolutePath);//D:\BaiduNetdiskDownload\a.txt

        File file1 = new File("a.txt");
        String absolutePath1 = file1.getAbsolutePath();
        System.out.println(absolutePath1);//D:\BaiduNetdiskDownload\a.txt
    }
}

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show02();
    }

    private static void show02() {
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\a.txt");
        File file1 = new File("a.txt");
        String path = file.getPath();
        String path1 = file1.getPath();
        System.out.println(path);
        System.out.println(path1);//a.txt
    }
}

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show03();
    }
    private static void show03() {
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\a.txt");
        String name = file.getName();
        System.out.println(name);//a.txt

    }
    
}

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show04();
    }

    private static void show04() {
        File file = new File("D:\\BaiduNetdiskDownload\\【非常重要】课程资料");
        long length = file.length();
        System.out.println(length);//4096
    }
 }

File类判断公共的方法

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    private static void show01() {
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\a.txt");
        System.out.println(file.exists());//false

    }

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    private static void show01() {
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled");
        if (file.exists()){//存在获取,不存在没有必要获取
            System.out.println(file.isDirectory());//true
            System.out.println(file.isFile());//false
        }
    }
}

File类创建删除功能的方法

public class t1 {
    public static void main(String[] args) throws IOException {
        show01();
    }
    private static void show01() throws IOException {
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\1.txt");
        boolean newFile = file.createNewFile();
        System.out.println(newFile);//true
    }
}

import java.io.File;

public class t1 {
    public static void main(String[] args){
        show01();
    }
    private static void show01(){
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\aaa");
        boolean newFile = file.mkdir();
        System.out.println(newFile);//true

        File file1 = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\aaa\\11\\cc");
        boolean newFile1 = file1.mkdirs();
        System.out.println(newFile);//true
    }
}

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    private static void show01(){
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled\\aaa");
        boolean delete = file.delete();
        System.out.println(delete);
    }
}

File类遍历文件夹目录功能

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    private static void show01(){
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled");
        String[] list = file.list();
        for (String s : list) {
            System.out.println(s);
        }
    }
}

import java.io.File;

public class t1 {
    public static void main(String[] args) {
        show01();
    }
    private static void show01(){
        File file = new File("C:\\Users\\陈卓宇\\IdeaProjects\\untitled");
        File[] list = file.listFiles();
        for (File s : list) {
            System.out.println(s);
        }
    }
}

返回结果