第五章 java中notify和notifyAll的区别


notify在这篇文章中,我们将看到 Java和Java 之间的区别notifyall

通知():

当您在对象上调用notify]方法时,它会唤醒等待该对象的线程之一。因此,如果多个线程正在等待一个对象,它将唤醒其中一个。现在你一定想知道它会唤醒哪一个。它实际上取决于操作系统的实现。

通知所有():

notifyAll 将唤醒等待该对象的所有线程,不像 notify 只唤醒其中一个。哪个将首先唤醒取决于线程优先级和操作系统实现。

让我们借助示例来理解它:

1. 创建一个名为 File.java 的类:

线程将在其上执行操作并调用等待和通知方法是 java bean 类。

package org.arpit.java2blog.thread;

public class File {

String name;
boolean isCompleted;

public File(String name) {
super();
this.name = name;
}

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public boolean isCompleted() {
return isCompleted;
}
public void setCompleted(boolean isCompleted) {
this.isCompleted = isCompleted;
}

}

2. 创建一个名为 FileReader.java 的类

这个线程会一直等到其他线程调用notify方法,然后才会完成它的处理。它将首先锁定文件对象,并从同步块中调用。因此在此示例中,它将等待 FileWriter 完成文件。

package org.arpit.java2blog.thread;

public class FileReader implements Runnable{

File file;

public FileReader(File file) {
  super();
  this.file = file;
}

@Override
public void run() {
  synchronized (file) {
   System.out.println(Thread.currentThread().getName()+" is waiting for the file to be completed: "+file.getName());
   try {
    file.wait();
   } catch (InterruptedException e) {    
    e.printStackTrace();
   }
   System.out.println(Thread.currentThread().getName()+": File has been completed now!! you can read it");
  }
}

}

3. 创建一个名为 FileWriter.java 的类

此类将通知正在等待文件对象的线程(在通知的情况下)。它不会在调用 notify 后立即放弃锁,它首先完成其同步块。所以在本例中,FileWriter 将完成文件并将其通知给 FileReaders。

package org.arpit.java2blog.thread;
public class FileWriter implements Runnable{

File file;

public FileWriter(File file) {
  super();
  this.file = file;
}

@Override
public void run() {
  synchronized (file) {
   System.out.println("Write is going to start writing the file : " +file.getName() );
   try {
    Thread.sleep(1000);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
   file.setCompleted(true);
   System.out.println("File has been completed now");

   file.notify();
   System.out.println("notify one reader");

  }
}
}

4. 创建类NotifyAndNotifyAllMain,java。

这是我们的主类,它将创建上述类的对象并运行它。

package org.arpit.java2blog.thread;

public class NotifyAndNotifyAllMain {

public static void main(String args[])
{
  // File object on which wait and notify method will be called
  File file=new File("Excel file");
  FileReader reader1=new FileReader(file);
  FileReader reader2=new FileReader(file);

  // FileReader threads which will wait for completion of file
  Thread thread1=new Thread(reader1,"Reader 1");
  Thread thread2=new Thread(reader2,"Reader 2");

  thread2.start();
  thread1.start();

  // To ensure both readers started waiting for the file
  try {
   Thread.sleep(3000);
  } catch (InterruptedException e) {

   e.printStackTrace();
  }
  // FileWriter thread which will notify once file get completed
  FileWriter fileWriter=new FileWriter(file);
  Thread fileWriterThread=new Thread(fileWriter);
  fileWriterThread.start();
}
}

在通知()的情况下:

当您运行上述程序时,您将获得以下输出:

Reader 2 is waiting for the file to be completed: Excel file
Reader 1 is waiting for the file to be completed: Excel file
Write is going to start writing the file : Excel file
File has been completed now
notify one reader
Reader 2: File has been completed now!! you can read it

所以在这里,两个 FileReader 线程(阅读器 1 和阅读器 2)正在等待文件完成,所以他们调用了 file.wait()。一旦 FileWriter 完成它的文件,它就会调用 file.notify() 并且 reader 2 线程启动并完成其处理。

在 notifyAll() 的情况下:

让我们将 FileWriter 类更改为调用 file.notifyAll()。

package org.arpit.java2blog.thread;
public class FileWriter implements Runnable{
File file;

public FileWriter(File file) {
  super();
  this.file = file;
}

@Override
public void run() {
  synchronized (file) {
   System.out.println("Write is going to start writing the file : " +file.getName() );
   try {
    Thread.sleep(1000);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
   file.setCompleted(true);
   System.out.println("File has been completed now");

   file.notifyAll();
   System.out.println("notify all readers");

  }
}
}

当你运行上面的程序时,你会得到以下输出:

Reader 2 is waiting for the file to be completed: Excel file
Reader 1 is waiting for the file to be completed: Excel file
Write is going to start writing the file : Excel file
File has been completed now
notify all readers
Reader 1: File has been completed now!! you can read it
Reader 2: File has been completed now!! you can read it

在 notifyAll() 的情况下,它会通知所有等待该对象的线程。


原文链接:https://codingdict.com/