Java线程：线程的同步与锁

一、同步问题提出
 
线程的同步是为了防止多个线程访问一个数据对象时，对数据造成的破坏。
例如：两个线程ThreadA、ThreadB都操作同一个对象Foo对象，并修改Foo对象上的数据。
 
public
class
Foo {
    private
int
x = 100;
    public
int
getX() {
        return
x;
    }
    public
int
fix(int
y) {
        x = x - y;
        return
x;
    }
}
 
public
class
MyRunnable implements
Runnable {
    private
Foo foo = new
Foo();
    public
static
void
main(String[] args) {
        MyRunnable r = new
MyRunnable();
        Thread ta = new
Thread(r, "Thread-A"
);
        Thread tb = new
Thread(r, "Thread-B"
);
        ta.start();
        tb.start();
    }
    public
void
run() {
        for
(int
i = 0; i < 3; i++) {
            this
.fix(30);
            try
{
                Thread.sleep(1);
            } catch
(InterruptedException e) {
                e.printStackTrace();
            }
    &