NO1
public class Main { public static class AddTest extends Thread { private static Integer num = 0; @Override public void run() { for (int i = 0; i < 1000; i++) { num = num + 1; System.out.println("now num is " + num); } } } public static void main(String[] args) throws Exception { for (int i = 0; i < 100; i++) { new AddTest().start(); } } }
NO2
public class Main { public static class AddTest extends Thread { private static Integer num = 0; private static Object lock = new Object(); @Override public void run() { for (int i = 0; i < 1000; i++) { synchronized (lock) { num = num + 1; System.out.println("now num is " + num); } } } } public static void main(String[] args) throws Exception { for (int i = 0; i < 100; i++) { new AddTest().start(); } } }
NO3
public class Main { public static class AddTest extends Thread { private static Integer num = 0; @Override public void run() { for (int i = 0; i < 1000; i++) { synchronized (num) { num = num + 1;// System.out.println("now num is " + num); } } } } public static void main(String[] args) throws Exception { for (int i = 0; i < 100; i++) { new AddTest().start(); } } }
NO4
public class Main { public static class AddTest extends Thread { private static Integer num = 0; private Integer lock = 0; //-128~127 @Override public void run() { for (int i = 0; i < 1000; i++) { synchronized (lock) { num = num + 1; System.out.println("now num is " + num); } } } } public static void main(String[] args) throws Exception { for (int i = 0; i < 100; i++) { new AddTest().start(); } } }
1 no
2 yes
3 no num=num+1,会生成另一个对象,锁就不唯一了
4 yes Integer 会缓存 -128(固定)~127(默认可配置) 的整数,所以无论多少个Integer(0) 都是一个对象