1. 线程是程序中单独顺序的控制流，线程本身依靠程序进行运行，线程是程序中的顺序控制流，只能使用分配给程序的资源和环境。
2. 进程是执行中的程序，一个进程可以包含一个或多个线程，但至少要包含一个线程。
3. 单线程是程序中只存在一个线程，实际上主方法就是一个主线程；多线程是在一个程序中运行多个任务，其目的是更好的使用CPU资源。
4. 在Java中，线程的实现有两种：继承Thread类和实现Runnable接口。Thread类是在java.lang包中定义的，继承Thread类必须重写run()方法。
例1：继承Thread类的线程
class MyThread extends Thread{
private String name;
public MyThread(String name){
this.name = name;
}
@Override
public void run() {
for(int i = 0; i < 10; i++){
System.out.println(name+":"+i);
}
super.run();
}
}
public class ThreadDemo01 {
public static void main(String[] args) {
MyThread t1 = new MyThread("A");
MyThread t2 = new MyThread("B");
// 线程的启动是通过start方法
t1.start();
t2.start();
}
}
例2：实现Runnable接口
class MyRunnable implements Runnable{
private String name;
public MyRunnable(String name){
this.name = name;
}
@Override
public void run() {
for(int i = 0; i < 100; i++){
System.out.println(name+":"+i);
}
}
}
public class ThreadDemo02 {
public static void main(String[] args) {
MyRunnable r1 = new MyRunnable("A");
MyRunnable r2 = new MyRunnable("B");
Thread t1 = new Thread(r1);
Thread t2 = new Thread(r2);
t1.start();
t2.start();
}
}
5. 线程的状态
(1) 创建状态：准备好了一个多线程的对象
(2) 就绪状态：调用了start()方法，等待CPU进行调度
(3) 运行状态：执行run()方法
(4) 阻塞状态：暂时停止执行，可能将资源交给其他线程使用
(5) 终止状态：线程销毁
6. 线程的常用方法
(1) getName()：取得线程名称
(2) currentThread()：取得当前线程对象
(3) isAlive()：判断线程是否启动
(4) join()：线程的强制运行
(5) sleep()：线程的休眠
(6) yield()：线程的礼让
例1：前五种方法的使用：
class RunnableDemo implements Runnable{
private String name;
public RunnableDemo(String name){
this.name = name;
}
public void run(){
for(int i = 0; i < 10; i++){
try {
// 1s执行一次
Thread.sleep(1000);
System.out.println(name+":"+Thread.currentThread().getName());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public class ThreadDemo03 {
public static void main(String[] args) {
RunnableDemo rd1 = new RunnableDemo("A");
Thread t1 = new Thread(rd1);
//System.out.println(t1.isAlive());
t1.start();
//System.out.println(t1.isAlive());
// 强行执行
for(int i = 0; i < 10; i++){
if(i > 5){
try {
t1.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("主线程:"+i);
}
RunnableDemo rd2 = new RunnableDemo("B");
Thread t2 = new Thread(rd2);
t2.start();
}
}
其结果为：
主线程:0
主线程:1
主线程:2
主线程:3
主线程:4
主线程:5
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
A:Thread-0
主线程:6
主线程:7
主线程:8
主线程:9
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
B:Thread-1
例2：礼让的使用
class RunnableDemo02 implements Runnable{
private String name;
public RunnableDemo02(String name){
this.name = name;
}
@Override
public void run(){
for(int i = 0; i < 10; i++){
System.out.println(name+":"+i);
if(i == 4){
System.out.println("礼让");
// 线程的礼让
Thread.yield();
}
}
}
}
public class ThreadDemo04 {
public static void main(String[] args) {
RunnableDemo02 r1 = new RunnableDemo02("A");
RunnableDemo02 r2 = new RunnableDemo02("B");
Thread t1 = new Thread(r1);
Thread t2 = new Thread(r2);
t1.start();
t2.start();
}
}
7. 线程的优先级，不一定会影响线程的执行顺序
优先级顺序设置：1-MIN-PRIORITY; 10-MAX-PRIORITY; 5-NORM-PRIORITY，默认值是5。
class RunnableDemo03 implements Runnable{
@Override
public void run() {
for(int i = 0; i < 5; i++){
try {
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName()+":"+i);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public class ThreadDemo05 {
public static void main(String[] args) {
Thread t1 = new Thread(new RunnableDemo03(),"A");
Thread t2 = new Thread(new RunnableDemo03(),"B");
Thread t3 = new Thread(new RunnableDemo03(),"C");
t1.setPriority(Thread.MIN_PRIORITY);
t2.setPriority(Thread.NORM_PRIORITY);
t3.setPriority(Thread.MAX_PRIORITY);
t1.start();
t2.start();
t3.start();
}
}
8. 同步
例1：同步代码块
class MyThread2 implements Runnable{
private int ticket = 5;
public void run(){
for(int i = 0; i < 10; i++){
synchronized(this){
if(ticket > 0){
try {
Thread.sleep(500);
System.out.println(Thread.currentThread().getName()+":"+ticket--);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}
public class ThreadDemo06 {
public static void main(String[] args) {
MyThread2 m = new MyThread2();
Thread t1 = new Thread(m);
Thread t2 = new Thread(m);
Thread t3 = new Thread(m);
t1.start();
t2.start();
t3.start();
}
}
例2：同步方法
class MyThread2 implements Runnable{
private int ticket = 5;
public void run(){
for(int i = 0; i < 10; i++){
method();
}
}
public synchronized void method(){
if(ticket > 0){
try {
Thread.sleep(500);
System.out.println(Thread.currentThread().getName()+":"+ticket--);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public class ThreadDemo06 {
public static void main(String[] args) {
MyThread2 m = new MyThread2();
Thread t1 = new Thread(m);
Thread t2 = new Thread(m);
Thread t3 = new Thread(m);
t1.start();
t2.start();
t3.start();
}
}
9. 线程的生命周期