class?CalTask?extends?RecursiveTask<Integer>{
??private?static?final?int?THRESHOLD=20;
????private?int?arr[];
????private?int?start;
????private??int?end;
????public?CalTask(int[]?arr,?int?start,?int?end)?{
super();
this.arr?=?arr;
this.start?=?start;
this.end?=?end;
????}
????@Override
????protected?Integer?compute()?{
int?sum=0;
if?(end-start<THRESHOLD)?{
????for?(int?i?=?start;?i?<?end;?i++)?{
????????????sum?+=?arr[i];
????}
????return?sum;
????}?else?{
????int?middle=(start+end)/2;
????CalTask?left=new?CalTask(arr,?start,?middle);
????CalTask?ringht=new?CalTask(arr,?middle,?end);
????left.fork();
????ringht.fork();
????return?left.join()+ringht.join();
?????}
????}
}
public?class?Sum?{
????public?static?void?main(String[]?args)?throws?InterruptedException,?ExecutionException?{
int[]?arr?=?new?int[100];
Random?rand?=?new?Random();
int?total?=?0;
for?(int?i?=?0;?i?<?arr.length;?i++)?{
int?tmp=rand.nextInt(20);
total+=(arr[i]=tmp);
}
System.out.println(total);
ForkJoinPool?pool=ForkJoinPool.commonPool();
Future<Integer>?future?=?pool.submit(new?CalTask(arr,0,arr.length));
System.out.println(future.get());
pool.shutdown();
????}
}無返回值的情況下已經(jīng)搞懂了但像這樣有返回值的情況下，compute方法else塊中最后 return left.join()+right.join();理解不了，請大神通俗的解釋一下另外這里fork()方法能說明一下嗎？書中居然沒有說，看例子就是執(zhí)行的意思？還有commPool的運行狀態(tài)不是說不受shutdown()影響嗎？那這里為何要有這個方法？
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