昨天去面試，面試官問了一個問題：Runnable和Thread有什么區別，因為針對這個問題以前有背過，並且網上大多數都是這些結論，所以脫口而出：
1.Thread有單繼承的問題；
2.Runnable便於實現資源共享，而Thread不能；
然而面試官好像並沒有什么表示。之后結束后我就找了一下度娘，得到了這篇文章：
https://blog.csdn.net/zhaojianting/article/details/97664370
突然發現“Runnable便於實現資源共享”這一優點好像並不合理，以下是我的代碼實現。
使用Thread實現多線程
public class MyThread extends Thread {
private int ticket = 5;
@Override
public void run() {
while (true) {
System.out.println("Thread ticket = " + ticket--);
if (ticket < 0) {
break;
}
}
}
}
public class Test {
public static void main(String[] args) {
//Test Thread
new MyThread().start();
new MyThread().start();
}
}
執行結果如下：
Thread ticket = 5
Thread ticket = 4
Thread ticket = 3
Thread ticket = 2
Thread ticket = 1
Thread ticket = 0
Thread ticket = 5
Thread ticket = 4
Thread ticket = 3
Thread ticket = 2
Thread ticket = 1
Thread ticket = 0
並不能實現資源共享，跟以前背的面試題答案一樣；但真的是這樣嗎？我們仔細看一下，代碼中我們創建了兩個MyThread對象，每個對象都有自己的ticket成員變量，當然會多賣1倍。現在我們重新測試一下，請看測試代碼：
public class Test {
public static void main(String[] args) {
//Test Thread
MyThread t1 = new MyThread();
new Thread(t1).start();
new Thread(t1).start();
}
}
測試結果如下：
Thread ticket = 5
Thread ticket = 4
Thread ticket = 3
Thread ticket = 2
Thread ticket = 1
Thread ticket = 0
Thread ticket = -1
可以看到這次我們只創建了一個MyThread對象，並沒出現賣兩倍票的情況，Thread也可以實現資源共享。
因為多線程訪問同一變量會有並發問題（需要加鎖），所以Thread正確的寫法如下：
public class MyThread extends Thread {
private int ticket = 5;
@Override
public void run() {
if (ticket > 0) {
synchronized (this) {
if (ticket > 0) {
while (true) {
System.out.println("Thread:" + Thread.currentThread().getName() + "--Thread ticket = " + ticket--);
if (ticket < 0) {
break;
}
}
}
}
}
}
}
public class Test {
public static void main(String[] args) {
//Test Thread
MyThread t1 = new MyThread();
new Thread(t1).start();
new Thread(t1).start();
new Thread(t1).start();
new Thread(t1).start();
new Thread(t1).start();
new Thread(t1).start();
}
}
執行結果如下：
Thread:Thread-1--Thread ticket = 5
Thread:Thread-1--Thread ticket = 4
Thread:Thread-1--Thread ticket = 3
Thread:Thread-1--Thread ticket = 2
Thread:Thread-1--Thread ticket = 1
Thread:Thread-1--Thread ticket = 0
現在看Thread和Runnable的源碼：
public
class Thread implements Runnable {
/* Make sure registerNatives is the first thing <clinit> does. */
private static native void registerNatives();
static {
registerNatives();
}
private volatile String name;
private int priority;
private Thread threadQ;
private long eetop;
@FunctionalInterface
public interface Runnable {
/**
* When an object implementing interface <code>Runnable</code> is used
* to create a thread, starting the thread causes the object's
* <code>run</code> method to be called in that separately executing
* thread.
* <p>
* The general contract of the method <code>run</code> is that it may
* take any action whatsoever.
*
* @see java.lang.Thread#run()
*/
public abstract void run();
}
結論：其實Thread也就是實現了Runnable接口，提供了更多的方法而已。所以說Thread與Runnable並沒有什么區別。如果硬要說有什么區別的話，那就是類與接口的區別，繼承與實現的區別。另外最重要的是，學習的時候不要忘了思考哦！