[英]When there is 2 object being declared in main method, the code is being compiled simultaneously?
我在这里调查多线程操作。 但我目前对主要方法执行顺序感到怀疑。 请向我解释这些,问题在下面标记。
这是我正在研究的一个简单程序
public class HelloWorld implements Runnable {
private Thread t;
private String threadname;
HelloWorld(String name){
threadname= name;
System.out.println("Create " +threadname);
}
public void run() {
System.out.println("Running " +threadname);
try {
for(int i=4; i>0;i--) {
System.out.println("Thread" +threadname +", "+i);
Thread.sleep(50);
}
}catch(InterruptedException e) {
System.out.println("Thread" +threadname +"interrupted ");
}
System.out.println("Thread" +threadname +"exiting ");
}
public void start() {
System.out.println("Starting " +threadname);
if(t==null)
{
t=new Thread(this, threadname);
t.start();
}
}
public static void main(String[] args) {
HelloWorld obj1= new HelloWorld ("Thread-1");
obj1.start();
HelloWorld obj2= new HelloWorld ("Thread-2");
obj2.start();
}
}
实际结果
Create Thread-1
Starting Thread-1
Create Thread-2
Starting Thread-2
Running Thread-1
ThreadThread-1, 4
Running Thread-2
ThreadThread-2, 4
ThreadThread-2, 3
ThreadThread-1, 3
ThreadThread-1, 2
ThreadThread-2, 2
ThreadThread-1, 1
ThreadThread-2, 1
ThreadThread-2exiting
ThreadThread-1exiting
我的问题:
Create Thread-1
Starting Thread-1
Create Thread-2(why here will switch from 1 to 2)
Starting Thread-2
Running Thread-1
ThreadThread-1, 4
Running Thread-2(At here, I understand the thread is switch when Thread.sleep(50) is being executed;)
ThreadThread-2, 4
ThreadThread-2, 3
ThreadThread-1, 3
ThreadThread-1, 2
ThreadThread-2, 2
ThreadThread-1, 1
ThreadThread-2, 1
ThreadThread-2exiting
ThreadThread-1exiting
问题:为什么这里会从1切换到2? main 方法中的 2 个对象是否同时运行?
这是因为您使用的是多线程,而多线程提供了并行执行。
在 main 方法中,您已经启动了两个子线程 obj1.start() 和 obj2.start()。 直到 obj1.start() 只有一个子线程(主线程是父线程)。 但是当您启动第二个子线程 obj2.start() 时,现在有两个子线程正在并行执行,这就是发生切换的原因。两个线程将有单独的执行路径并将并行运行。
此外,由于 CPU 使用了线程调度算法(轮询等),因此正在发生切换。
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