JUC线程进阶篇08：线程中常见的8中用锁情况
标签： 多线程
在工作用，多线程中对是否加上synchronized，是否加上static等，8种常见的用锁的情况
8种情况
题目
判断打印的”one” or “two”??
1.两个普通同步方法，两个线程，标准打印，结果：one two
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number.getTwo();
}
}).start();
}
}
class Number{
public synchronized void getOne(){
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
}2.新增Thread.sleep()给getOne(),结果：one two
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number.getTwo();
}
}).start();
}
}
class Number{
public synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
}3.新增普通方法getThree(),结果：three one two
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number.getTwo();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number.getThree();
}
}).start();
}
}
class Number{
public synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
public void getThree(){
System.out.println("Three");
}
}4.两个普通同步方法，两个对象，结果：two one
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number1 = new Number();
final Number number2 = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number1.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number2.getTwo();
}
}).start();
}
}
class Number{
public synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
}5.修改getOne()为静态同步方法，结果：two one
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number1 = new Number();
final Number number2 = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number1.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number2.getTwo();
}
}).start();
}
}
class Number{
public static synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
}6.修改两个方法均为静态同步方法，一个对象，结果：one two
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number1 = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number1.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number1.getTwo();
}
}).start();
}
}
class Number{
public static synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public static synchronized void getTwo(){
System.out.println("Two");
}
}7.一个静态同步方法，一个非静态同步方法，两个对象，结果：two one
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number1 = new Number();
final Number number2 = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number1.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number2.getTwo();
}
}).start();
}
}
class Number{
public static synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public synchronized void getTwo(){
System.out.println("Two");
}
}8.两个静态同步方法，两个对象，结果：one two
public class TestThread8Monitor {
public static void main(String[] args) {
final Number number1 = new Number();
final Number number2 = new Number();
new Thread(new Runnable() {
@Override
public void run() {
number1.getOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
number2.getTwo();
}
}).start();
}
}
class Number{
public static synchronized void getOne(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("one");
}
public static synchronized void getTwo(){
System.out.println("Two");
}
}总结
其实这八种用法的区别关键在于以下两点：
非静态方法的锁默认为this，静态方法的锁为对应的class实例（这里是NUmber.class）
某一个时刻内，只能有一个线程持有锁，无论有几个方法
