几道基础的线程题

第一题

　　子线程循环十次，每次从1加到10，最后在主线程中相加得到结果?

 1 public class CallableTest {
 2     public static void main(String[] args) {
 3         ThreadDemo demo = new ThreadDemo();
 4         
 5         FutureTask<Integer> result = new FutureTask<Integer>(demo);
 6         
 7         int sum = 0;
 8         for(int i = 0;i < 10;i++){
 9             Thread thread = new Thread(result);
10             thread.start();
11             try {
12                 Integer num = result.get();
13                 sum += num;
14             } catch (InterruptedException e) {
15                 e.printStackTrace();
16             } catch (ExecutionException e) {
17                 e.printStackTrace();
18             }
19         }
20         
21         System.out.println(sum);
22     }
23     
24 }
25 
26 class ThreadDemo implements Callable<Integer> {
27     @Override
28     public Integer call() throws Exception {
29         int sum = 0;
30         for(int i = 1;i <= 10;i++){
31             sum += i;
32         }
33         return sum;
34     }
35 }

第二题

　　设计 4 个线程，其中两个线程每次对 j 增加 1，另外两个线程对 j 每次减少
　　1。写出程序。

 1 public class AddSubThread {
 2     public static void main(String[] args) {
 3         Operater operater = new Operater();
 4         ThreadDemoAdd add = new ThreadDemoAdd(operater);
 5         ThreadDemoSub sub = new ThreadDemoSub(operater);
 6         
 7         while(true) {
 8             for(int i = 0;i < 2;i++){
 9                 new Thread(add).start();
10             }
11             
12             for(int i = 0;i < 2;i++){
13                 new Thread(sub).start();
14             }
15         }
16     }
17 }
18 
19 class ThreadDemoAdd implements Runnable{
20     private Operater operater;
21     
22     public ThreadDemoAdd(Operater operater){
23         this.operater = operater;
24     }
25     
26     @Override
27     public void run() {
28         operater.add();
29     }
30     
31 }
32 
33 class ThreadDemoSub implements Runnable {
34 　　private Operater operater;
35     
36     public ThreadDemoSub(Operater operater){
37         this.operater = operater;
38     }
39 
40     @Override
41     public void run() {
42         operater.sub();
43     }
44     
45 }
46 
47 class Operater {
48     private int i = 0;
49     
50     public synchronized void add(){
51         i++;
52         System.out.println("i :" + i);
53     }
54     
55     public synchronized void sub(){
56         i--;
57         System.out.println("i :" + i);
58     }
59 }