先说java中实现多线程常用的两种方式：
1：继承Thread类，并重写run()方法
2：实现Runnable接口，实现run方法
实际上Thread类也是实现了Runnable接口
[Java]
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public
class
Thread
implements
Runnable {
........
｝
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而Runnable接口只定义了一个run方法
[AppleScript]
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@FunctionalInterface
public interface Runnable
{
/
*
*
*
When an object implementing interface
<
code
>
Runnable
<
/
code
>
is
used
*
to
create a thread
,
starting
the
thread causes
the
object
's
*
<
code
>
run
<
/
code
>
method
to
be called
in
that
separately executing
*
thread.
*
<
p
>
*
The general contract
of
the
method
<
code
>
run
<
/
code
>
is
that
it
may
*
take any action whatsoever.
*
*
@see java.lang.Thread
#run()
*
/
public abstract void
run
(
)
;
}
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我们需要实现的多线程业务逻辑，都需要在run方法内实现。
而start()是Thread中定义的方法，以下是start()方法的源码
[Java]
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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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start()通过调用本地native方法start0来启动一个线程，本地方法内最终会调用run方法，这样就可以实现在另一个线程中运行我们需要的代码。
而单独运行run()方法，就跟我们调用普通接口实现方法一样了，并不会启动新的线程.
总结：
1、start()方法运行时，本地启动新的线程，线程中会调用run方法，程序不需要等待run方法执行完毕再执行后面的程序;
2、run()方法是我们编写需要新的线程执行代码的方法，单独运行是不会有多线程效果的。
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