[英]When there is 2 object being declared in main method, the code is being compiled simultaneously?
我在這里調查多線程操作。 但我目前對主要方法執行順序感到懷疑。 請向我解釋這些,問題在下面標記。
這是我正在研究的一個簡單程序
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();
}
}
實際結果
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
我的問題:
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
問題:為什么這里會從1切換到2? main 方法中的 2 個對象是否同時運行?
這是因為您使用的是多線程,而多線程提供了並行執行。
在 main 方法中,您已經啟動了兩個子線程 obj1.start() 和 obj2.start()。 直到 obj1.start() 只有一個子線程(主線程是父線程)。 但是當您啟動第二個子線程 obj2.start() 時,現在有兩個子線程正在並行執行,這就是發生切換的原因。兩個線程將有單獨的執行路徑並將並行運行。
此外,由於 CPU 使用了線程調度算法(輪詢等),因此正在發生切換。
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