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Java实现线程的三种方式
Java实现线程的三种方式:
  1. 1.
    继承Thread
  2. 2.
    实现Runnable接口
  3. 3.
    实现Callable接口

1. 区别:

  1. 1.
    第一种方式继承Thread就不能继承其他类了,后面两种可以;
  2. 2.
    使用后两种方式可以多个线程共享一个target;
  3. 3.
    Callable比Runnable多一个返回值,并且call()方法可以抛出异常;
  4. 4.
    访问线程名,第一种直接使用this.getName(),后两种使用Thread.currentThread().getName()。
下面我们通过代码来看一下实现和区别:

2. 三种实现:

//1. 继承Thread,重写run()方法
class Thread1 extends Thread {
private int n = 5;
@Override
public void run() {
while(n > 0) {
System.out.println("name:" + this.getName() + ", n:" + n);
n--;
}
}
}
//2. 实现Runnable接口,实现run()方法
class Thread2 implements Runnable {
private int n = 5;
@Override
public void run() {
while(n > 0) {
System.out.println("name:" + Thread.currentThread().getName() + ", n:" + n);
n--;
}
}
}
//3. 实现Callable接口,实现call()方法,带有返回值和异常
class Thread3 implements Callable<String> {
private int n = 5;
@Override
public String call() throws Exception {
while(n > 0) {
System.out.println("name:" + Thread.currentThread().getName() + ", n:" + n);
n--;
}
return String.valueOf(n);
}
}
如何使用:
//第一种实现方式
Thread1 t11 = new Thread1();
Thread1 t12 = new Thread1();
Thread1 t13 = new Thread1();
t11.start();
t12.start();
t13.start();
//第二种实现方式
Thread2 t21 = new Thread2();
Thread2 t22 = new Thread2();
Thread2 t23 = new Thread2();
Thread t211 = new Thread(t21);
Thread t212 = new Thread(t22);
Thread t213 = new Thread(t23);
t211.start();
t212.start();
t213.start();
//第三种实现
Thread3 t31 = new Thread3();
Thread3 t32 = new Thread3();
Thread3 t33 = new Thread3();
FutureTask<String> f1 = new FutureTask<>(t31);
FutureTask<String> f2 = new FutureTask<>(t32);
FutureTask<String> f3 = new FutureTask<>(t33);
Thread t311 = new Thread(f1);
Thread t312 = new Thread(f2);
Thread t313 = new Thread(f3);
t311.start();
t312.start();
t313.start();
从代码可以看出以上提到的区别1,3,4。那么区别2共享一个target是什么意思呢?
首先我们看一下上述代码的运行结果,
第一种:
name:Thread-1, n:5
name:Thread-1, n:4
name:Thread-1, n:3
name:Thread-1, n:2
name:Thread-1, n:1
name:Thread-2, n:5
name:Thread-2, n:4
name:Thread-2, n:3
name:Thread-2, n:2
name:Thread-2, n:1
name:Thread-0, n:5
name:Thread-0, n:4
name:Thread-0, n:3
name:Thread-0, n:2
name:Thread-0, n:1
第二种:
name:Thread-4, n:5
name:Thread-4, n:4
name:Thread-4, n:3
name:Thread-3, n:5
name:Thread-5, n:5
name:Thread-3, n:4
name:Thread-4, n:2
name:Thread-4, n:1
name:Thread-3, n:3
name:Thread-3, n:2
name:Thread-3, n:1
name:Thread-5, n:4
name:Thread-5, n:3
name:Thread-5, n:2
name:Thread-5, n:1
可以看到,这两种方式的结果一样,都是new了三个线程,每个线程内部循环5次。第二种方式并没有体现共用同一个target。如果我们将第二种创建线程的方式改为:
//第二种实现方式
Thread2 t21 = new Thread2();
Thread2 t22 = new Thread2();
Thread2 t23 = new Thread2();
Thread t211 = new Thread(t21);
Thread t212 = new Thread(t21);
Thread t213 = new Thread(t21);
t211.start();
t212.start();
t213.start();
看一下运行结果:
name:Thread-4, n:5
name:Thread-4, n:4
name:Thread-4, n:3
name:Thread-4, n:2
name:Thread-4, n:1
name:Thread-3, n:5
name:Thread-5, n:5
可以看到,虽然也启动了3个线程,但是由于共享一个target,n的值改变了,其他两个线程也会知道,所以因此一共循环了5次。但是这里明明是7次啊,这是由于多线程的同步问题,可以给run方法加上synchronized关键字解决:
@Override
public synchronized void run() {
while(n > 0) {
System.out.println("name:" + Thread.currentThread().getName() + ", n:" + n);
n--;
}
}
运行结果:
name:Thread-3, n:5
name:Thread-3, n:4
name:Thread-3, n:3
name:Thread-3, n:2
name:Thread-3, n:1
这里可能有点迷惑,只启动了一个线程啊。其实另外两个线程也启动了,只是这个时候n=0无法进入循环。我们可以加一行打印:
@Override
public synchronized void run() {
System.out.println("进入" + Thread.currentThread().getName() + "线程");
while(n > 0) {
System.out.println("name:" + Thread.currentThread().getName() + ", n:" + n);
n--;
}
}
可以看到运行结果:
进入Thread-3线程
name:Thread-3, n:5
name:Thread-3, n:4
name:Thread-3, n:3
name:Thread-3, n:2
name:Thread-3, n:1
进入Thread-5线程
进入Thread-4线程
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1. 区别:
2. 三种实现: