synchronized关键字的三种用法
注：java提供了两种锁机制，一种是内置的锁synchronized，另一种是显示的Lock对象
1.synchronized直接指定加锁对象
对给定对象加锁，进入同步代码前要获得给定对象的锁
package 并发;
public class FirstThread implements Runnable{
public void run() {
synchronized (this) {
for(int i=0;i<5;i++) {
System.out.println(Thread.currentThread().getName()+" "+i);
}
}
}
public static void main(String[] args) {
FirstThread task=new FirstThread();
Thread thread1=new Thread(task);
Thread thread2=new Thread(task);
Thread thread3=new Thread(task);
thread1.start();
thread2.start();
thread3.start();
}
}
2.synchronized作用于非静态方法
相当于对当前对象加锁，进入同步代码前要获得当前对象的锁
package 并发;
public class FirstThread implements Runnable{
public synchronized void run() {
for(int i=0;i<5;i++) {
System.out.println(Thread.currentThread().getName()+" "+i);
}
}
public static void main(String[] args) {
FirstThread task=new FirstThread();
Thread thread1=new Thread(task);
Thread thread2=new Thread(task);
Thread thread3=new Thread(task);
thread1.start();
thread2.start();
thread3.start();
}
}
3.synchronized作用于静态方法
相当于对当前类加锁，进入同步代码前要获得当前类的锁
package 并发;
public class FirstThread implements Runnable{
public static synchronized void count() {
for(int i=0;i<5;i++) {
System.out.println(Thread.currentThread().getName()+" "+i);
}
}
public void run() {
count();
}
public static void main(String[] args) {
FirstThread task=new FirstThread();
Thread thread1=new Thread(task);
Thread thread2=new Thread(task);
Thread thread3=new Thread(task);
thread1.start();
thread2.start();
thread3.start();
}
}
重点！！！
- 对象锁：
synchronized修饰非静态方法、代码块synchronized (this)和synchronized (非this对象)，加锁的是对象 - 类锁：
synchronized修饰静态方法、代码块的synchronized (类.class)，加锁的是类
