1.start()方法来启动线程,真正实现了多线程运行,这时无需等待run方法体代码执行完毕而直接继续执行下面的代码:
通过调用Thread类的start()方法来启动一个线程,
这时此线程是处于就绪状态,
并没有运行。
然后通过此Thread类调用方法run()来完成其运行操作的,
这里方法run()称为线程体,
它包含了要执行的这个线程的内容,
Run方法运行结束,
此线程终止,
而CPU再运行其它线程,
2.run()方法当作普通方法的方式调用,程序还是要顺序执行,还是要等待run方法体执行完毕后才可继续执行下面的代码:
而如果直接用Run方法,
这只是调用一个方法而已,
程序中依然只有主线程--这一个线程,
其程序执行路径还是只有一条,
这样就没有达到写线程的目的。
通过implements Runnable接口来实现多线程
示例代码:
代码如下 |
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package com;
public class TestRunnable implements Runnable{
private int num = 0;
public static void main(String[] args) {
for(int i=0; i<5; i++){
new Thread(new TestRunnable(i)).start();
}
}
public TestRunnable(int num) {
this.num = num;
}
//实现方法
public void run(){
System.out.println("线程:"+this.num);
}
}
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上例打印出来的结果是无序的:
1 4 3 2 0
也可能是别的顺序,通过Thread类调用start,真正实现了多线程,不用等待run方法执行完毕再起新线程。
如果将
代码如下 |
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new Thread(new TestRunnable(i)).start()
改成
new Thread(new TestRunnable(i)).run(),
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则打印出来的结果是由顺序的,也就是:
0 1 2 3 4
通过Thread类直接调用run方法,实际上就是调用TestRunnable类的run方法,查看Thread类的run方法:
代码如下 |
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public void run() {
if (target != null) {
target.run();
}
}
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发现Thread类run方法就是调用了TestRunnable的run(),所以通过
代码如下 |
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new Thread(new TestRunnable(i)).run()
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并不是多线程,其执行线程还是主线程。
下面再将Thread类的start方法贴出来,可与上面Thread类的run方法做个对比:
代码如下 |
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/**
* Causes this thread to begin execution; the Java Virtual Machine
* calls the run method of this thread.
*
* The result is that two threads are running concurrently: the
* current thread (which returns from the call to the
* start method) and the other thread (which executes its
* run method).
*
* It is never legal to start a thread more than once.
* In particular, a thread may not be restarted once it has completed
* execution.
*
* @exception IllegalThreadStateException if the thread was already
* started.
* @see #run()
* @see #stop()
*/
public synchronized void start() {
/**
* This method is not invoked for the main method thread or "system"
* group threads created/set up by the VM. Any new functionality added
* to this method in the future may have to also be added to the VM.
*
* A zero status value corresponds to state "NEW".
*/
if (threadStatus != 0)
throw new IllegalThreadStateException();
/* Notify the group that this thread is about to be started
* so that it can be added to the group's list of threads
* and the group's unstarted count can be decremented. */
group.add(this);
boolean started = false;
try {
start0();
started = true;
} finally {
try {
if (!started) {
group.threadStartFailed(this);
}
} catch (Throwable ignore) {
/* do nothing. If start0 threw a Throwable then
it will be passed up the call stack */
}
}
}
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