class Printer {
public static void print1() {
synchronized(Printer.class){ //锁对象可以是任意对象,但是被锁的代码需要保证是同一把锁,不能用匿名对象
System.out.print("程");
System.out.print("序");
System.out.print("员");
System.out.print("\r\n");
}
}
/*
* 非静态同步函数的锁是:this
* 静态的同步函数的锁是:字节码对象
*/
public static synchronized void print2() {
System.out.print("码");
System.out.print("农");
System.out.print("\r\n");
}
}
public class Demo2_Synchronized {
/**
* @param args
* 需求:铁路售票,一共100张,通过四个窗口卖完.
*/
public static void main(String[] args) {
TicketsSeller t1 = new TicketsSeller();
TicketsSeller t2 = new TicketsSeller();
TicketsSeller t3 = new TicketsSeller();
TicketsSeller t4 = new TicketsSeller();
t1.setName("窗口1");
t2.setName("窗口2");
t3.setName("窗口3");
t4.setName("窗口4");
t1.start();
t2.start();
t3.start();
t4.start();
}
}
class TicketsSeller extends Thread {
private static int tickets = 100;
static Object obj = new Object();
public TicketsSeller() {
super();
}
public TicketsSeller(String name) {
super(name);
}
public void run() {
while(true) {
synchronized(obj) {
if(tickets <= 0)
break;
try {
Thread.sleep(10);//线程1睡,线程2睡,线程3睡,线程4睡
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(getName() + "...这是第" + tickets-- + "号票");
}
}
}
}
单例设计模式: 保证类在内存中只有一个对象
如何保证类在内存中只有一个对象呢?
单例写法
//饿汉式
class Singleton {
//1,私有构造函数
private Singleton(){}
//2,创建本类对象
private static Singleton s = new Singleton();
//3,对外提供公共的访问方法
public static Singleton getInstance() {
return s;
}
public static void print() {
System.out.println("11111111111");
}
}
//懒汉式,单例的延迟加载模式
class Singleton {
//1,私有构造函数
private Singleton(){}
//2,声明一个本类的引用
private static Singleton s;
//3,对外提供公共的访问方法
public static Singleton getInstance() {
if(s == null)
//线程1,线程2
s = new Singleton();
return s;
}
public static void print() {
System.out.println("11111111111");
}
}
class Singleton {
private Singleton() {}
public static final Singleton s = new Singleton();//final是最终的意思,被final修饰的变量不可以被更改
}