线程以及三种同步方法

1.线程和并发的思维导图：

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2.并发和并行：

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3.进程和线程：

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4.多线程的优势：

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5.Java操作进程

1 public static void main(String[] args) throws IOException {
2         //Java中如何开启一个进程  如记事本
3         //方式一：使用Runtime类的exec方法
4         Runtime rt = Runtime.getRuntime();
5         rt.exec("notepad");
6         //方式二：processBuilder的start方法
7         ProcessBuilder pb = new ProcessBuilder("notepad");
8         pb.start();
9     }

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6.创建和启动线程

 1 class MusicThread extends Thread{//定义的MusicThread类继承自Thread
 2     @Override
 3     public void run() {
 4         for(int i = 0; i < 50 ; i++) {
 5             System.out.println("听音乐..." + i); 
 6         }
 7     }
 8 }
 9 public class ExtendsThreadDemo {
10     public static void main(String[] args)  {
11         //主线程  运行游戏
12         for(int i = 0; i <50; i++) {
13             System.out.println("打游戏..." + i);
14             if(i == 10) {
15                 //创建线程对象并且启动
16                 MusicThread musicThread = new MusicThread();
17                 musicThread.start();//不能调用run方法
18             }
19         }
20     }
21 }

 1 class MusicThreadImpl implements Runnable{
 2     @Override
 3     public void run() {
 4         for(int i = 0; i < 50 ; i++) {
 5             System.out.println("听音乐..." + i); 
 6         }
 7     }
 8 }
 9 public class ExtendsThreadDemo {
10     public static void main(String[] args)  {
11         //主线程  运行游戏
12         for(int i = 0; i <50; i++) {
13             System.out.println("打游戏..." + i);
14             if(i == 10) {
15                 //创建线程对象并且启动
16                 MusicThreadImpl target = new MusicThreadImpl();
17                 Thread thread = new Thread(target);
18                 thread.start();
19             }
20         }
21     }
22 }

 1     public static void main(String[] args)  {
 2         //主线程  运行游戏
 3         for(int i = 0; i <50; i++) {
 4             System.out.println("打游戏..." + i);
 5             if(i == 10) {
 6                 //创建线程对象并且启动
 7                 //匿名内部类 方式一：
 8                 new Thread(new Runnable() {
 9                     
10                     @Override
11                     public void run() {
12                         for(int i = 0; i < 50 ; i++) {
13                             System.out.println("听音乐..." + i); 
14                         }
15                     }
16                 }).start();
17             }
18         }
19     }

 1 public static void main(String[] args)  {
 2         //主线程  运行游戏
 3         for(int i = 0; i <50; i++) {
 4             System.out.println("打游戏..." + i);
 5             if(i == 10) {
 6                 //创建线程对象并且启动
 7                 //匿名内壁类 方式一：
 8              new Thread() {
 9                  public void run() {
10                      for(int i = 0; i < 50; i++) {
11                          System.out.println("听音乐" + i);
12                      }
13                  }
14              }.start();
15             }
16         }
17     }

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7.两种方式对比：引例吃苹果比赛

 1 //方式一   继承Thread类
 2 class Person extends Thread{
 3     private int num = 50;
 4     public Person(String name) {
 5         super(name);//调用父类构造器
 6     }
 7     public void run(){
 8         for(int i = 0; i < 50; i ++) {
　　　　　　　　　if(num > 0){
 9             System.out.println(getName() + "吃了" + "第" + num-- +"个苹果")};//getName是Thread中的方法 获取线程的名称
10         }
11     }
12 }
13 public class ExtendsThread {
14     public static void main(String[] args)  {
15      //一共50个苹果 3个同学吃
16         Person p1 = new Person("A");
17         p1.start();
18         Person p2 = new Person("B");
19         p2.start();
20         Person p3 = new Person("C");
21         p3.start();
22     }
23 }

结果：每个同学都吃了50个苹果，上图中有具体原因。

 1 //方式二   实现Runnable接口
 2 class Person implements Runnable{
 3     private int num = 50;
 4     public void run(){
 5         for(int i = 0; i < 50; i++) {
 6             if(num > 0) {
 7                 System.out.println(Thread.currentThread().getName()+ "吃了" + "第" + num-- +"个苹果");
 8             }
 9         }
10     }
11 }
12 public class  ImplementsDemo {
13     public static void main(String[] args)  {
14      //一共50个苹果 3个同学吃
15         Person a  = new Person();
16         new Thread(a, "A").start();
17         new Thread(a, "B").start();
18         new Thread(a, "C").start();
19     }
20 }

吃苹果比赛分析继承方式和实现方式的区别

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8.线程不安全问题的分析：

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9.解决线程不安全的两种方法：

方法一：synchronized代码块

 1     public void run() {
 2             for (int i = 0; i < 50; i++) {
 3                 synchronized (this) {
 4                 if (num > 0) {
 5                     try {
 6                         Thread.sleep(10);
 7                     } catch (InterruptedException e) {
 8                         e.printStackTrace();
 9                     }
10                     System.out.println(Thread.currentThread().getName() + "吃了" + num-- + "号苹果");
11                 }
12             }
13         }
14     }

方法二：synchronized方法：

 1     public void run() {
 2         eat();
 3     }
 4 
 5     private void eat() {
 6         for (int i = 0; i < 50; i++) {
 7             synchronized (this) {
 8                 if (num > 0) {
 9                     try {
10                         Thread.sleep(10);
11                     } catch (InterruptedException e) {
12                         e.printStackTrace();
13                     }
14                     System.out.println(Thread.currentThread().getName() + "吃了" + num-- + "号苹果");
15                 }
16             }
17         }
18 
19     }
20 }

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9.synchronized的好与坏：

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10。同步锁

class Apple implements Runnable{
    
    private int num = 5000;
    private final Lock locks = new ReentrantLock();
    @Override
    public void run() {
        for(int i = 0; i < 500; i ++) {
        eat();
        }
    }
    private void eat() {
        locks.lock();
        try {
            if(num > 0)
                    System.out.println(Thread.currentThread().getName() + " eat " + num + "th " + "apple");
                    Thread.sleep(10);
                    num --;
            
        }catch (Exception e) {
            e.printStackTrace();
        }
        finally {
            locks.unlock();
        }
    }
    
}
public class LockDemo {
    public static void main(String[] args) {
        Apple a = new Apple();
        new Thread(a, "A").start();;
        new Thread(a, "B").start();;
        new Thread(a, "S").start();
    }
}

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