多线程入门--synchronized介绍

线程安全

/**

* Allocates a new {@code Thread} object. This constructor has the same

* effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}

* {@code (null, target, name)}.

*

* @param  target

*         the object whose {@code run} method is invoked when this thread

*         is started. If {@code null}, this thread's run method is invoked.

*

* @param  name

*         the name of the new thread

*/

public Thread(Runnable target, String name) {

init(null, target, name, 0);

}

实现多线程的资源共享：

public class Test {
public static void main(String[] args) {
Thread1 thread1 = new Thread1();
Thread a = new Thread(thread1, "A");
Thread b = new Thread(thread1, "B");
Thread c = new Thread(thread1, "C");
Thread d = new Thread(thread1, "D");
Thread e = new Thread(thread1, "E");

a.start();
b.start();
c.start();
d.start();
e.start();
}
}

线程定义：

public class Thread1 extends Thread {
private int count=5;

@Override
public void run() {
super.run();
count--;
System.out.println(Thread.currentThread().getName() + " is running!");
System.out.println(Thread.currentThread().getName() + " count: " + count);
}
}

虽然共享了资源，但是对资源count的访问是不同步的。

A is running!
A count: 2
C is running!
B is running!
C count: 0
E is running!
D is running!
E count: 0
B count: 0
D count: 0

@Override
synchronized public void run() {
super.run();
count--;
System.out.println(Thread.currentThread().getName() + " count: " + count);
System.out.println(Thread.currentThread().getName() + " is running!");
}