public class PrintThread extends Thread {
private String msg;
public PrintThread(String msg) {
this.msg = msg;
}
public void run() {
for(int i = 0; i < 10000; i++) {
System.out.print(msg);
}
}

public static void main(String[] args {
new PrintThread("Good!").start();
new PrintThread("Nice!").start();
}
}

在main()方法里，先建立PrintThread类的实例后，调用该实例的start()方法启动线程。建立“PrintThread类的实例”和“启动该实例所对应的线程”是两个完全不同的处理。即使已经建立了实例，仍然必须等到调用start()方法才会启动线程。主线程在main()方法里启动两个线程，因为main()方法会立即结束，所以主线程也会立即结束，不过整个程序还没有结束，一直要等到所有线程都已经结束，程序才会结束。不过这里不包括daemon thread。利用Runnable接口

Runnable接口是java.lang Package里的接口，声明方法如下：

public interface Runnable {public abstract void run();}已实现Runnable接口的类必须实现run()方法。

public class PrintThread implements Runnable {
private String msg;
public PrintThread(String msg) {
this.msg = msg;
}
public void run() {
for(int i = 0; i < 10000; i++) {
System.out.print(msg);
}
}

public static void main(String[] args {
new Thread(new PrintThread("Good!")).start();
new Thread(new PrintThread("Nice!")).start();
}
}

使用该模式来限制同时只让一个线程运行。先看一个不是使用该模式的多线程的例子，并非线程安全（Thread-safe）的Gate类：

public class Main {
public static void main(String[] args) {
System.out.println("Testing Gate, hit CTRC+C to exit.");
Gate gate = new Gate();
new UserThread(gate, "Alice", "Alaska").start();
new UserThread(gate, "Bobby", "Brazil").start();
new UserThread(gate, "Chris", "Canada").start();
}
}

public class Gate {
private int counter = 0;
private String name = "Nobody";
private String address = "Nowhere";
public void pass(String name, String address) {
this.counter++;
this.name = name;
this.address = address;
check();
}
public String toString() {
return "No. " + counter + " name: " + name + ", address: " + address;
}
private void check() {
if (name.charAt(0) != address.charAt(0)) {
System.out.println("******BROKEN*******" + toString());
}
}

public class UserThread extends Thread {
private final Gate gate;
private final String myname;
private final String myaddress;
public UserThread (Gate gate, String myname, String myaddress) {
this.gate = gate;
this.myname = myname;
this.myaddress =myaddress;
}
public void run() {
System.out.println(this.myname + "Begin");
while(true) {
gate.pass(this.myname,myaddress);
}
}
}
}

执行看看。

由于Gate类不是线程安全的，当多个线程对其的状态进行更改时，会出现与期望不符的结果。可以通过将Gate类改造成线程安全的类来解决这个问题。线程安全最简单的方法即是使用本模式，使同一时间只让一个线程执行。线程安全版的Gate类如下：

public class Gate {
private int counter = 0;
private String name = "Nobody";
private String address = "Nowhere";
public synchronized void pass(String name, String address) {
this.counter++;
this.name = name;
this.address = address;
check();
}
public synchronized String toString() {
return "No. " + counter + " name: " + name + ", address: " + address;
}
private void check() {
if (name.charAt(0) != address.charAt(0)) {
System.out.println("******BROKEN*******" + toString());
}
}
}