synchronized是Java中的关键字，是一种同步锁。它修饰的对象有以下几种：
1. 修饰一个代码块，被修饰的代码块称为同步语句块，其作用的范围是大括号{}括起来的代码，作用的对象是调用这个代码块的对象；
2. 修饰一个方法，被修饰的方法称为同步方法，其作用的范围是整个方法，作用的对象是调用这个方法的对象；
3. 修改一个静态的方法，其作用的范围是整个静态方法，作用的对象是这个类的所有对象；
4. 修改一个类，其作用的范围是synchronized后面括号括起来的部分，作用主的对象是这个类的所有对象。
问题：
class test1{
public static synchronized void t11()
public synchronized void t12()
public synchronized void t13()
public void t14()
}
这几个函数哪几个之间存在竞争关系？
Synchronized ：锁住的是对象，出现synchronized表示随后的代码块要用到共享数据了，要锁住了。
Synchronized 4种形式。
1、synchronized(obj)：可以任意指定对象.
2、synchronized(this)：当前对象：当一个类加到内存时，常量池有一个地址直接指向当前正在执行的对象.
3、public synchronized void run()：当前对象（this），这是实例方法，每一方法里存着一个This.方法
对象：可以是普通类 public class Test {}, 也可以是干活线程类 ,只要是new 类名 的所有对象。
4、public static synchronized void test () : 由类加载器加载的class字节码文件（XXX.class、this.getClass）
到这里上面的问题就知道答案：t12与t13 之间存在竞争关系
下面我们开始验证public static synchronized void test () 与public synchronized void run()形式的同步锁，采用前两种的表现形式作为比较项：
一、首先验证public synchronized void run()
public class MainClass implements Runnable{
public int num = 100;
public boolean flag = true;
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
@Override
public void run() {
if (flag) {
while (true) {
synchronized (this) {//同步代码块
if(num>0){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"1--------"+num--);
}
}
}
} else {
while (true) {
this.salt();
}
}
}
public synchronized void salt(){
if(num > 0){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"2....."+num--);
}
}
public static void main(String[] args) {
MainClass main = new MainClass();
HashMap<String, Thread> hashMap = new HashMap<>();
//实例化thread对象，并放到hashmap中
for (int i = 0; i < 10; i++) {
Thread threadq = new Thread(main);
hashMap.put("thread for all "+ i, threadq);
}
//遍历hashmap，依次开启线程
Iterator<Entry<String, Thread>> Iterator = hashMap.entrySet().iterator();
while (Iterator.hasNext()) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
Thread thread = Iterator.next().getValue();
thread.start();
if(main.isFlag()){
main.setFlag(false);
}else{
main.setFlag(true);
}
}
}
}
输出结果：
Thread-02.....100
Thread-02.....99
Thread-02.....98
Thread-91--------97
Thread-82.....96
Thread-82.....95
Thread-82.....94
Thread-71--------93
Thread-62.....92
Thread-51--------91
Thread-42.....90
Thread-42.....89
Thread-31--------88
Thread-22.....87
Thread-11--------86
Thread-11--------85
Thread-11--------84
Thread-11--------83
Thread-22.....82
Thread-22.....81
Thread-31--------80
Thread-42.....79
Thread-51--------78
Thread-62.....77
Thread-62.....76
Thread-71--------75
Thread-71--------74
Thread-71--------73
Thread-82.....72
Thread-82.....71
Thread-82.....70
Thread-91--------69
Thread-02.....68
Thread-02.....67
Thread-91--------66
Thread-82.....65
Thread-82.....64
Thread-82.....63
Thread-82.....62
Thread-82.....61
Thread-82.....60
Thread-82.....59
Thread-82.....58
Thread-82.....57
Thread-82.....56
Thread-82.....55
Thread-71--------54
Thread-62.....53
Thread-62.....52
Thread-62.....51
Thread-51--------50
Thread-51--------49
Thread-42.....48
Thread-42.....47
Thread-42.....46
Thread-42.....45
Thread-31--------44
Thread-22.....43
Thread-11--------42
Thread-22.....41
Thread-22.....40
Thread-31--------39
Thread-31--------38
Thread-31--------37
Thread-31--------36
Thread-31--------35
Thread-31--------34
Thread-31--------33
Thread-31--------32
Thread-31--------31
Thread-42.....30
Thread-51--------29
Thread-51--------28
Thread-51--------27
Thread-51--------26
Thread-51--------25
Thread-51--------24
Thread-62.....23
Thread-62.....22
Thread-62.....21
Thread-62.....20
Thread-71--------19
Thread-71--------18
Thread-71--------17
Thread-82.....16
Thread-91--------15
Thread-02.....14
Thread-02.....13
Thread-91--------12
Thread-82.....11
Thread-82.....10
Thread-82.....9
Thread-82.....8
Thread-71--------7
Thread-71--------6
Thread-62.....5
Thread-62.....4
Thread-51--------3
Thread-42.....2
Thread-31--------1
二、验证public static synchronized void run()锁
public class MainStaticClass implements Runnable {
private static int num ;
private boolean flag = true;
private static CountDownLatch lanch;
public MainStaticClass(int num1,CountDownLatch lanch1){
lanch = lanch1;
num = num1;
}
public boolean isFlag() {
eturn flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
@Override
public void run() {
if (flag) {
while (true) {
synchronized (this.getClass()) {
if(num>0){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"-1----------"+num--);
lanch.countDown();
}
}
}
} else {
while(true){
salt();
}
}
}
public static synchronized void salt(){
if(num>0){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"-2----------"+num--);
lanch.countDown();
}
}
public static void main(String[] args) {
CountDownLatch countDownLatch = new CountDownLatch(100);
MainStaticClass main = new MainStaticClass(100,countDownLatch);
HashMap<String, Thread> hashMap = new HashMap<>();
for (int i = 0; i < 10; i++) {
Thread threadq = new Thread(main);
hashMap.put("thread for all "+ i, threadq);
}
Iterator<Entry<String, Thread>> Iterator = hashMap.entrySet().iterator();
while (Iterator.hasNext()) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
Thread thread = Iterator.next().getValue();
thread.start();
if(main.isFlag()){
main.setFlag(false);
}else{
main.setFlag(true);
}
}
try {
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
MainStaticClass main1 = new MainStaticClass(100,countDownLatch);
for (int i = 0; i < 10; i++) {
Thread threadq = new Thread(main1);
hashMap.put("thread for all "+ i, threadq);
}
Iterator<Entry<String, Thread>> Iterator1 = hashMap.entrySet().iterator();
while (Iterator1.hasNext()) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
Thread thread = Iterator1.next().getValue();
thread.start();
if(main1.isFlag()){
main1.setFlag(false);
}else{
main1.setFlag(true);
}
}
}
}
