title: Java 学习笔记
date: 2017-06-23 11:29:39

Mac配置java环境

• 第一步： vi .zshrc
• 第二步： 将这段文字输入 export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home
  export PATH=$JAVA_HOME/bin:$PATH
• 第三步： 输入source .zshrc 这样就可以使得环境变量起作用了
• 第四步： echo $JAVA_HOME看看有没有输出刚才配置的路径

Class JavaLaunchHelper is implemented in both... 报错处理

//  Go to ➤ (Help | Edit Custom Properties...) 
idea_rt
idea.no.launcher=true

创建一个简单的demo

一. 打开textEdit软件 设置:preferences > Format > Plain text 创建hello.java文件

``` java
public class hello{
    public static void main(String[] args){
        System.out.println("hello world");
    }
}
```

二. 找到当前文件目录 注意文件夹名字和类名一致(源程序)

javac hello.java

三. 生成一个hello.class的文件,然后执行（字节码程序）

java hello

乘法口诀

// i 代表行数
for(int i=1;i<=9;i++){
     for(int j=1;j<=i;j++){
         System.out.print(j + " * " + i + " = " + (i*j) + "\t");
     }
     System.out.println()
}
            

Java数组的可变参数

public class app {
    public static void main(String[] args) {
//        第一种传递数组
        double[] arr1 = {10.0, 23.0, 12.0, 13};
        double sum = getSum(arr1);
//        第二种传递方式(可变参数)
        double sum = getSum(0.8, 123.0, 2341, 3, 3.0);  //单个放在前面，避免歧义
        System.out.println(sum);
    }
    static double getSum(double cutoff, double... arr) {
        double sum = 0;
        for (double price : arr) {
            sum += price * cutoff;
        }
        return sum;
    }
}

java.util.Arrays 工具

public class array {
    public static void main(String[] args) {
        int[] arr = {1, 34, 5, 5, 65, 7, 76, 33};
        // 打印
        String arrString = java.util.Arrays.toString(arr);
        System.out.println(arrString);
        // 排序
        java.util.Arrays.sort(arr, 2, 6);
        System.out.println(java.util.Arrays.toString(arr));
        // 二分法
        int index = java.util.Arrays.binarySearch(arr,5);
        System.out.println(index);
    }
}

java中的变量(成员变量和局部变量)：

this存在与两个位置。

  -构造器中：表示当前创建的对象
  -方法中：那个调用this调用的方法，this表示那一个对象

class User {
    private String name;     // 私有变量默认是null
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;    // this的使用
    }
    public void showThis (){
        System.out.println(this.name);
    }
}

public class thisDemo {
    public static void main(String[] args) {
//        创建user1对象
        User user1 = new User();
        user1.setName("lily");
        String name = user1.getName();
        System.out.println(name);
//        创建user2对象
        User user2 = new User();
        user2.setName("lucy");
        // this的调用
        user1.showThis();
        user2.showThis();
    }
}

面向对象-子类初始化过程

class Animal {
    private String name;
    private int age;

    public void Fly() {
        System.out.println("会飞翔");
    }

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

}
// 继承Animal这个类
class Fish extends Animal {
    private String color;

    Fish(String name, int age, String color) {
        super(name, age);   // 父类私有变量赋值
        this.color = color;
    }

    // override 覆盖父类的方法
    public void Fly() {
        System.out.println("我会游泳");
        System.out.println(color + ", " + getName() + super.getAge());
    }
}


public class Superdemo {
    public static void main(String[] args) {
        Fish fish = new Fish("金枪鱼", 5, "yello");
        fish.Fly();
        String name = fish.getName();
        System.out.println(name);
        
        Object obj = "ABC";
    //  instanceof 判断对象是否是某一个类的实例
        System.out.println(obj instanceof Object);  //true
        System.out.println(obj instanceof String);  //true
    //  getClass()获取对象的实例类型
        System.out.println(obj.getClass() == String.class);  //true
    }
}

包装类的缓存

        // 缓存区间[-128,127],超出区间创建一个新空间
//        Integer i1 = new Integer(250);  //创建一个对象
//        Integer i1 = Integer.valueOf(250); // 手动装箱
        Integer i1 = 250;   // 自动装箱
        int i = Integer.valueOf(i1);  //拆箱
        String str = String.valueOf(i1); //数字转字符串
        int num = Integer.parseInt(str);  // 字符串转数字
        Integer i2 = 250;
        System.out.println(i1 == i2);      //false
        System.out.println(i1.equals(i2)); //true

模版方法的设计

// 模版方法
abstract class TemplateFn {
    // 算法的骨架
    final public long getTime() {
        long beginTime = System.currentTimeMillis();
        // callback
        dowork();
        long endime = System.currentTimeMillis();
        return endime - beginTime;
    }

    // 子类必须覆盖
    protected abstract void dowork();

}

// 拼接字符串
class StringDemo extends TemplateFn {
    protected void dowork() {
        String str = "";
        for (int i = 0; i < 10000; i++) {
            str += i;
        }
    }
}

// 加法
class AddNumDemo extends TemplateFn {
    protected void dowork() {
        int sum = 0;
        for (int i = 0; i < 10000; i++) {
            sum += 1;
        }
    }
}

public class TemplateDemo {
    public static void main(String[] args) {
        System.out.println(new StringDemo().getTime());
        System.out.println(new AddNumDemo().getTime());
    }
}

单例方法和枚举方法运用

//    单例模式
class Arrays {

    /**
     * 1.必须在该类中创建一个对象
     * 2.私有化自身的构造器
     * 3.暴露自己的一个方法
     */

    private static Arrays arrays = new Arrays();

    private Arrays() {
    }

    public static Arrays getArrays() {
        return arrays;
    }


    public void sort(int[] a) {
        System.out.println("数字排序成功");
    }
}

// 枚举代替单例
enum Arrays {
    arrays;

    public void sort(int[] a) {
        System.out.println("数字排序成功");
    }
}
public class human {
    public static void main(String[] args) {
//        单例方法
        Arrays.getArrays().sort(null);
//        枚举方法
        Arrays.arrays.sort(null);
    }
}

日期格式化（SimpleDateFormat、Calendar）

//SimpleDateFormat格式化日期
package com.controller;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateformatDemo {
    public static void main(String[] args) {
        Date d = new Date();
        System.out.println(d);
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss E");
        System.out.println(df.format(d));
        try {
            System.out.println(df.parse("2017-07-28 17:52:32 Fri"));
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}
//Calendar创建日期
import java.util.Calendar;
import java.util.Date;
public class CalendarDemo {
    public static void main(String[] args) {
        //创建日历对象
        Calendar c = Calendar.getInstance();
        System.out.println(c);
        System.out.println("年"+c.get(Calendar.YEAR));
        System.out.println("月"+(c.get(Calendar.MONTH)+1));
        System.out.println("日"+c.get(Calendar.DATE));
        System.out.println("时"+c.get(Calendar.HOUR_OF_DAY));
        System.out.println("分"+c.get(Calendar.MINUTE));
        System.out.println("秒"+c.get(Calendar.SECOND));

        // Calendar 转换成 Date
        Date d = c.getTime();
        System.out.println(d);

        // 给指定的日期添加和减去指定的时间量
        c.add(Calendar.DATE,1);
        System.out.println(c.getTime());
    }
}

Scanner获取用户的输入。

import java.util.Scanner;

public class ScannerDemo {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        System.out.println("next方式接收");
        // 判断是否还有输入
        if (scanner.hasNext()) {
            String str1 = scanner.nextLine();
            System.out.println("输入的数据为：" + str1);
        }
        /**
         *  输入平均数
         */
        Scanner scan = new Scanner(System.in);
        double sum = 0;
        int m = 0;
        while (scan.hasNextDouble()) {
            double x = scan.nextDouble();
            m += 1;
            sum += x;
        }
        System.out.println(m + "个数的和为" + sum);
        System.out.println(m + "个数的平均值是" + (sum / m));
    }
}

Runtime和ProcessBuilder运行环境

import java.io.IOException;
public class ProcessDemo {
    public static void main(String[] args) throws IOException {
        Runtime runtime = Runtime.getRuntime();
        runtime.exec("ifconfig");
        ProcessBuilder ps = new ProcessBuilder("ifconfig");
        ps.start();
    }
}

Java 流(Stream)、文件(File)和IO

import java.io.*;

public class FileSreamDemo {
    //删除文件及目录
    public static void deleteFolder(File folder) {
        File[] files = folder.listFiles();
        if (files != null) {
            for (File f : files) {
                if (f.isDirectory()) {
                    deleteFolder(f);
                } else {
                    f.delete();
                }
            }
        }
        folder.delete();
    }

    public static void main(String args[]) {

        /**
         * 创建目录
         */
        String dirname = "/tmp/user/java/bin";
        File dir = new File(dirname);
        dir.mkdirs();
        /**
         * 删除目录
         */
        File d = new File("/tmp/user/java/bin");
        deleteFolder(d);
        try {
            /**
             * 写入数据
             */
            FileOutputStream fop = new FileOutputStream("test.txt");
            OutputStreamWriter writer = new OutputStreamWriter(fop, "UTF-8");
            byte[] bWrite = {1, 3, 4, 5, 6};
            for (int i = 0; i < bWrite.length; i++) {
                System.out.println(new String(String.valueOf(bWrite[i])));
                writer.append(String.valueOf(bWrite[i]));
            }
            writer.close();    // 关闭读取流
            fop.close();       // 关闭输入流,释放系统资源

            /**
             * 读数据
             */
            FileInputStream fip = new FileInputStream("test.txt");
            InputStreamReader reader = new InputStreamReader(fip, "UTF-8");
            StringBuffer sb = new StringBuffer();
            while (reader.ready()) {
                sb.append((char) reader.read());
                // 转成char加到StringBuffer对象中
            }
            System.out.println(sb.toString());
            reader.close();
            fip.close();

        } catch (IOException e) {
            System.out.print("Exception");
        }
    }
}

Map集合中的keyset方法遍历(LinkedHashMap,HashMap)

public class MapDemo {

    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<String, Integer>();
        // 添加值
        map.put("a", 1);
        map.put("b", 1);
        map.put("c", 1);
        // 删除值
        map.remove("c");
        System.out.println(map);
        // 获取值
        System.out.println(map.get("a"));

        /**
         * 1.调用map的ketset方法所有的集合存到set集合中
         * 2。遍历set，获取每个元素
         * 3。调用get方法，获取每个对应的值
         */
        Set<String> set = map.keySet();
        System.out.println(set.getClass());
        Iterator<String> it = set.iterator();

        while (it.hasNext()) {
            String key = it.next();
            Integer value = map.get(key);
            System.out.println(key + "..." + value);
        }
        for (String i : map.keySet()) {
            Integer value = map.get(i);
            System.out.println(i + "..." + value);
        }
      /**
         * 1。调用map中的entrySet将集合中的集合映射关系，存储到Set集合
         * 2。迭代set集合
         * 3。获取集合元素是映射关系
         * 4。通过映射对象方法getkey,getValue获取健值对
         */
        Set<Map.Entry<String, Integer>> entryset = map.entrySet();
        Iterator<Map.Entry<String, Integer>> it = entryset.iterator();
        while (it.hasNext()) {
            Map.Entry<String, Integer> entry = it.next();
            String key = entry.getKey();
            Integer value = entry.getValue();
            System.out.println(key + "..." + value);
        }
        for(Map.Entry<String, Integer> entry:map.entrySet()){
            String key = entry.getKey();
            Integer value = entry.getValue();
            System.out.println(key + "..." + value);
        }
    }
}

Java IO file的用法

import java.io.File;
import java.io.IOException;

public class javaIOdemo {
    public static void main(String[] args) {

        File file = new File("/Users/shangri-la/Sites");
        String pathSeparator = File.pathSeparator;
        String separator = File.separator;

        File file1 = new File("/Users", "shangri-la/Sites");
        System.out.println(file1);   //  /Users/shangri-la/Sites

        System.out.println(pathSeparator);  //  :
        System.out.println(separator);     //   /
        System.out.println(file);     //   /Users/shangri-la/Sites

        try {
            creatFile();
            mkDir();

        } catch (IOException e) {
            e.printStackTrace();
        }
        delete();
        getName();
        getFiles();
    }

    // 创建文件
    public static void creatFile() throws IOException {
        File file = new File("/Users/shangri-la/Sites/a.txt");
        //只能创建文件，不能创建文件夹
        boolean b = file.createNewFile();
        System.out.println(b);
    }

    /**
     * 创建文件
     * mkdir
     * mkdirs 创建多文件夹
     *
     * @throws IOException
     */
    public static void mkDir() throws IOException {
        File file = new File("/Users/shangri-la/Sites/abc");
        boolean b = file.mkdirs();
        System.out.println(b);
    }

    /**
     * 删除文件／文件夹
     *
     * @throws IOException
     */
    public static void delete() {
        File file = new File("/Users/shangri-la/Sites/abc");
        boolean b = file.delete();
        System.out.println(b);
    }

    /**
     * String getName()
     * 获取文件夹／文件名字
     * String path  获取字符串路径
     * long length
     * Srting getAbsoluteFile()   获取绝对路径 String
     * File getAbsoluteFile()     获取绝对路径 File
     * String getParent     获取父路径
     * File getParentFile   获取父路径
     * boolean exists  判断路径是否存在
     * boolean isDirectory  判断是不是文件夹
     * boolean isFile  判断是不是文件夹
     */
    public static void getName() {
        File file = new File("/Users/shangri-la/Sites/abc.text");
        String name = file.getName();
        String path = file.getPath();
        Long lenth = file.length();
        File absolutefile = file.getAbsoluteFile();
        System.out.println(name);
        System.out.println(absolutefile);
        System.out.println(path);
        System.out.println(lenth);

        File parentFile = file.getParentFile().getParentFile().getParentFile().getParentFile();
        System.out.println(parentFile);
        Boolean b = file.exists();
        Boolean c = file.isFile();
        System.out.println(b);
    }

    public static void getFiles() {
        File file = new File("/Users/shangri-la/Sites");
        String[] fileNames = file.list();
        for (String fileName : fileNames) {
            System.out.println(fileName);
        }
    }

}

FileFilter过滤器

// 1.创建DirectoryDome过滤器文件
import java.io.File;
import java.io.FileFilter;

/**
 * FileFilter过滤器
 */

public class DirectoryDome implements FileFilter {

    public boolean accept(File pathname) {
        if (pathname.isDirectory())
            return true;
        return pathname.getName().toLowerCase().endsWith(".java");
    }
}
// 2.创建MyFilterDemo主函数文件
import filter.DirectoryDome;

import java.io.File;

public class MyFilterDemo {
    public static void main(String[] args) {
        getAllJava(new File("/Users/shangri-la/Sites"));
    }

    public static void getAllJava(File dir) {
        File[] files = dir.listFiles(new DirectoryDome()); //添加过滤器
        for (File f : files) {
            if (f.isDirectory()) {
                getAllJava(f);
            } else {
                if ("b.java".equals(f.getName()))
                    System.out.println(f.getName());
            }
        }
    }
}

FileOutputStream输出流的用法

import java.io.FileOutputStream;

public class FileOutputStreamDemo {
    public static void main(String[] args) throws Exception {
        /**
         * 续写 FileOutputStream 第二个参数为true
         * /r/n 换行
         */
        FileOutputStream fos = new FileOutputStream("/Users/shangri-la/a.txt");
        fos.write(97);
        byte[] bytes = {65,66,67,68};
        fos.write(bytes);
        fos.write(bytes,1,2);  //从哪开始，写几个
        fos.write("hello\r\n".getBytes());
        fos.write("word".getBytes());
        fos.close();
    }
}
// 写流的标准语法
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamDemo {
    public static void main(String[] args) throws Exception {
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream("/Users/shangri-la/b.txt");
            fos.write(97);
        } catch (IOException ex) {
            ex.printStackTrace();
            throw new RuntimeException("文件写入失败！请重试");
        } finally {
            try {
                if(fos!=null)
                fos.close();
            } catch (IOException ex) {
                System.out.println(ex.toString());
            }
        }
    }
}

复制粘贴文件字符数组

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class copyFileDemo {
    public static void main(String[] args) {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("/Users/shangri-la/c.txt");
            fw = new FileWriter("/Users/shangri-la/d.txt");
            char[] ch = new char[1024];
            int len = 0;
            while ((len = fr.read(ch)) != -1) {
                fw.write(ch, 1, len);
                fw.flush();
            }
        } catch (IOException ex) {
            System.out.println(ex.toString());
        } finally {
            try {
                if (fw != null)
                    fw.close();
            } catch (IOException ex) {
                throw new RuntimeException("释放资源失败");
            } finally {
                try {
                    if (fr != null)
                        fr.close();
                } catch (IOException ex) {
                    throw new RuntimeException("释放资源失败");
                }
            }
        }
    }
}

转换流（InputStreamReader和OutputStreamWriter）

import java.io.*;

public class InputStreamReaderDemo {
    public static void main(String[] args) throws IOException {
        FileInputStream fis = new FileInputStream("/Users/shangri-la/c.txt");
        // 输出流的转换流
        InputStreamReader fsr = new InputStreamReader(fis, "GBK");
        char[] ch = new char[1024];
        int len = 0;
        while ((len = fsr.read(ch)) != -1) {
            System.out.println(new String(ch, 0, len));
        }
        fsr.close();

        // 缓存输入流 （提高写入速率）
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("/Users/shangri-la/c.txt"));
        // 输入流的转换流
        OutputStreamWriter osw = new OutputStreamWriter(fos,"GBK");
        osw.write("你好");
        osw.close();

       //-------------- 写入一个bytes数组 --------------------
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("/Users/shangri-la/d.txt"));
        bos.write(90);
        bos.flush();
        byte[] bytes = "hello".getBytes();    // 字符串转换成byte类型并且存入一个byte数组中 new String(bytes)还原
        bos.write(bytes);
        bos.write(bytes, 0, 2);
        bos.close();
    }
}

文件复制方式【字节流】，四种方式速度大比拼

/**
 *  文件复制方式，字节流，四种方式
 *  1. 字节流读写单个字节                  125250 毫秒
 *  2. 字节流读写字节数组                  193    毫秒  OK
 *  3. 字节缓冲区读写单个字节。             1210   毫秒
 *  4. 字节缓冲区流读写字节数组              73     毫秒  OK
 */
public class Copy {
    public static void main(String[] args)throws IOException {
        long s = System.currentTimeMillis();
        copy_4(new File("c:\\q.exe"), new File("d:\\q.exe"));
        long e = System.currentTimeMillis();
        System.out.println(e-s);
    }
    /*
     *  4. 字节缓冲区流读写字节数组
     */
    public static void copy_4(File src,File desc)throws IOException{
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(src));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(desc));
        int len = 0 ;
        byte[] bytes = new byte[1024];
        while((len = bis.read(bytes))!=-1){
            bos.write(bytes,0,len);
        }
        bos.close();
        bis.close();
    }
    /*
     *   3. 字节缓冲区读写单个字节。   
     */
    public static void copy_3(File src,File desc)throws IOException{
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(src));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(desc));
        int len = 0 ;
        while((len = bis.read())!=-1){
            bos.write(len);
        }
        bos.close();
        bis.close();
    }
    
    /*
     *   2. 字节流读写字节数组      
     */
    public static void copy_2(File src,File desc)throws IOException{
        FileInputStream fis = new FileInputStream(src);
        FileOutputStream fos = new FileOutputStream(desc);
        int len = 0 ;
        byte[] bytes = new byte[1024];
        while((len = fis.read(bytes))!=-1){
            fos.write(bytes,0,len);
        }
        fos.close();
        fis.close();
    }
    
    /*
     * 1.字节流读写单个字节
     */
    public static void copy_1(File src,File desc)throws IOException{
        FileInputStream fis = new FileInputStream(src);
        FileOutputStream fos = new FileOutputStream(desc);
        int len = 0 ;
        while((len = fis.read())!=-1){
            fos.write(len);
        }
        fos.close();
        fis.close();
    }
}

IO流整理

打印流实现文本复制

import java.io.*;
/**
 * 打印流实现文本复制
 * 读取数据源 BufferedReader + FileReader 读取文本行
 * 写入数据目的  PrintWriter + Println 自动刷新
 */
public class printWriteDemo {
    public static void main(String[] args) throws IOException {
        BufferedReader bfr = new BufferedReader(new FileReader("/Users/shangri-la/c.txt"));
        PrintWriter pw = new PrintWriter(new FileWriter("/Users/shangri-la/a.txt"), true);
        String line = null;
        while ((line = bfr.readLine()) != null) {
            pw.println(line);
        }
        pw.close();
        bfr.close();
    }
}

获取线程的名称及线程的sleep方法

1. ThreadDemo 类
package controller.Thread;

public class ThreadDemo {
    /**
     * 每个线程都有自己的名字
     * 运行的方法main线程，名字就是main
     * 其他新建的线程，默认名字都是"Thread-0"
     * static Thread currentThread() 返回正在执行的线程对象
     * 
     * 接口的另一种实现方法
     * 创建Thread类，传递Runavle接口实现类
     * 调用Thread类的start（）方法
     */
    public static void main(String[] args) throws InterruptedException {
        System.out.println(new Thread().currentThread().getName());
        // 第一种方法
        new SleepThread().start();
        // 第二种方法（接口方式Runable）
        RunableDemo rd = new RunableDemo();
        new Thread(rd).start();

        /**
         * 匿名内部类的实现程序
         * new 父类的接口(){
         *    重新的方法
         *  }
         */
        new Thread() {
            public void run() {
                System.out.println("匿名内部类的实现");
            }
        }.start();

        // 实现接口方式 XXX implements Runable {public void run (){}}
        Runnable r = new Runnable() {
            public void run() {
                System.out.println("匿名接口内部类");
            }
        };
        new Thread(r).start();
        // 实现接口方式的第二种方法
        new Thread(new Runnable() {
            public void run() {
                System.out.println("匿名接口内部类");
            }
        }).start();
    }
}
2. SleepThread 类
package controller.Thread;

public class SleepThread extends Thread{
    public void run(){
        for (int i = 0; i < 5; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(i);
        }
        System.out.println(getName());
    }
}
3.实现 Runnable，重写run方法
package controller.Thread;

/**
 * 接口的另一种实现方法
 * 实现 Runnable，重写run方法
 */

public class RunableDemo implements Runnable {

    public void run() {
        System.out.println("runable");
    }
}

线程池的使用

package controller.Thread;


import java.util.concurrent.*;

public class ThreadPoolDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService es = Executors.newFixedThreadPool(2);
        System.out.println(es);
        es.submit(new Runnable() {
            public void run() {
                System.out.println(Thread.currentThread().getName() + " 匿名接口内部类1");
            }
        });
        es.submit(new Runnable() {
            public void run() {
                System.out.println(Thread.currentThread().getName() + " 匿名接口内部类2");
            }
        });

        es.submit(new Runnable() {
            public void run() {
                System.out.println(Thread.currentThread().getName() + " 匿名接口内部类3");
            }
        });
        es.shutdown();

        /**
         * callable接口方式实现线程
         *  实现步骤
         *      工厂类Executors静态方法 newFixedThreadPool方法，创建线程池对象
         *      submit（callabel c）
         */

        ExecutorService es1 = Executors.newFixedThreadPool(2);
        Future f = es1.submit(new Callable() {
            public String call() throws Exception {
                return "abc";
            }
        });
        System.out.println(f.get());
        es1.shutdown();
    }
}

使用多线程技术，求和

// 1.MultThreadPool 类
package controller.Thread;

import java.util.concurrent.*;

/**
 * 使用多线程技术，求和
 * 两个线程
 * 第1个是1+...+100
 * 第2个是1+...+200
 */
public class MultThreadPool {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService es = Executors.newFixedThreadPool(2);

        Future f1 = es.submit(new GetSumCallable(100));
        Future f2 = es.submit(new GetSumCallable(200));

        System.out.println(f1.get());
        System.out.println(f2.get());
        es.shutdown();
    }
}
// 1.GetSumCallable 接口类
package controller.Thread;

import java.util.concurrent.Callable;

public class GetSumCallable implements Callable<Integer> {
    private int a;

    public GetSumCallable(int a) {
        this.a = a;
    }

    public Integer call() throws Exception {
        int sum = 0;
        for (int i = 0; i < a; i++) {
            sum += i;
        }
        return sum;
    }
}

采用同步方法形式,解决线程的安全问题

// 1. TicketDemo 类
package controller.TicketDemo;

public class TicketDemo {
    public static void main(String[] args) {
        Tickets tickets = new Tickets();
        Thread t0 = new Thread(tickets);
        Thread t1 = new Thread(tickets);
        Thread t2 = new Thread(tickets);
        t0.start();
        t1.start();
        t2.start();
    }
}
// Tickets 接口
package controller.TicketDemo;

/**
 * 采用同步方法形式,解决线程的安全问题
 * 好处: 代码简洁
 * 将线程共享数据,和同步,抽取到一个方法中
 * 在方法的声明上,加入同步关键字
 * 问题:
 * 同步方法有锁吗,肯定有,同步方法中的对象锁,是本类对象引用 this
 * 如果方法是静态的呢,同步有锁吗,绝对不是this
 * 锁是本类自己.class 属性
 * 静态方法,同步锁,是本类类名.class属性
 */

public class Tickets implements Runnable {
    private int tickets = 100;

    public void run() {
        while (true) {
            payTicket();
        }
    }

    public synchronized void payTicket() {
        if (tickets > 0) {
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + " 第" + tickets-- + "张");
        }
    }
}

java线程中的死锁实现

//1. 创建LockA
package controller.deadLock;

public class LockA {
    private LockA() {
    }

    public static final LockA locka = new LockA();
}
// 2.创建LockB
package controller.deadLock;

public class LockB {
    private LockB() {
    }

    public static final LockB lockb = new LockB();
}
// 3. 利用奇偶数实现synchronized的同步锁
package controller.deadLock;

public class DeadLock implements Runnable {
    private int i = 0;

    public void run() {
        while (true) {
            if (i % 2 == 0) {
                synchronized (LockA.locka) {
                    System.out.println(" 先进入A再进入B   LockA");
                    synchronized (LockB.lockb) {
                        System.out.println(" 先进入A再进入B   LockB");
                    }
                }
            } else {
                synchronized (LockB.lockb) {
                    System.out.println(" 先进入B再进入A  LockB");
                    synchronized (LockA.locka) {
                        System.out.println(" 先进入B再进入A   LockA");
                    }
                }
            }
            i++;
        }

    }
}
// 4. DeadLockDemo方法调用
package controller.deadLock;

public class DeadLockDemo {
    public static void main(String[] args) {
        DeadLock deadLock = new DeadLock();
        Thread t1 = new Thread(deadLock);
        Thread t2 = new Thread(deadLock);
        t1.start();
        t2.start();
    }
}