修飾實例方法，作用於當前實例加鎖，進入同步代碼前要獲得當前實例的鎖；實例鎖，一個實例一把鎖

修飾靜態方法，作用於當前類對象加鎖，進入同步代碼前要獲得當前類對象的鎖；對象鎖，一個對象一把鎖

修飾代碼塊，指定加鎖對象，對給定對象加鎖，進入同步代碼庫前要獲得給定對象的鎖；對象鎖，一個對象一把鎖

實例鎖
public class SuperHakceTest implements Runnable{

    public static Integer flag = 0;

    public synchronized void instanse(){
        flag ++;
    }

    @Override
    public void run() {
        for(int i = 0;i < 1000;i ++){
            instanse();
        }
    }

    public static void main(String[] args) throws Exception{
        SuperHakceTest superHakceTest = new SuperHakceTest();
        Thread thread1 = new Thread(superHakceTest);
        Thread thread2 = new Thread(superHakceTest);
        Thread thread3 = new Thread(superHakceTest);
        thread1.start();thread2.start();thread3.start();
        thread1.join();thread2.join();thread3.join();
        System.out.println("LAST FLAG = " + SuperHakceTest.flag);
    }

}

對象鎖
public class SuperHakceTest implements Runnable{

    public static Integer flag = 0;

    public static synchronized void instanse(){
        flag ++;
    }

    @Override
    public void run() {
        for(int i = 0;i < 1000;i ++){
            instanse();
        }
    }

    public static void main(String[] args) throws Exception{
        SuperHakceTest superHakceTest1 = new SuperHakceTest();
        SuperHakceTest superHakceTest2 = new SuperHakceTest();
        SuperHakceTest superHakceTest3 = new SuperHakceTest();
        Thread thread1 = new Thread(superHakceTest1);
        Thread thread2 = new Thread(superHakceTest2);
        Thread thread3 = new Thread(superHakceTest3);
        thread1.start();thread2.start();thread3.start();
        thread1.join();thread2.join();thread3.join();
        System.out.println("LAST FLAG = " + SuperHakceTest.flag);
    }

}

//this,當前實例對象鎖
synchronized(this){
    for(int j=0;j<1000000;j++){
        i++;
    }
}

//class對象鎖
synchronized(AccountingSync.class){
    for(int j=0;j<1000000;j++){
        i++;
    }
}
 

Java並發之synchronized