java Long 不能取消引用
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Long cannot be dereferenced
提问by
I did almost everything to solve the annoying issue with "Long cannot be dereferenced", but anything worked out. Thus, can anyone please, help me? The problem is when I check if program timed out in if(System.currentTimeMillis().longValue()==finish), the comparison is not working.
我几乎尽一切努力解决了“Long无法取消引用”的烦人问题，但一切都解决了。因此，任何人都可以请帮助我吗？问题是当我检查程序是否超时时if(System.currentTimeMillis().longValue()==finish)，比较不起作用。
public void play()
{
long begin = System.currentTimeMillis();
long finish = begin + 10*1000;
while (found<3 && System.currentTimeMillis() < finish) {
Command command = parser.getCommand();
processCommand(command);
}
if(System.currentTimeMillis().longValue()==finish){
if(found==1){System.out.println("Time is out. You found "+found+" item.");}
else if(found>1 && found<3){System.out.println("Time is out. You found "+found+" items.");}}
else{
if(found==1){System.out.println("Thank you for playing. You found "+found+" item.");}
else if(found>1 && found<3){System.out.println("Thank you for playing. You found "+found+" items.");}
else{System.out.println("Thank you for playing. Good bye.");}
}
}
采纳答案by davidxxx
System.currentTimeMillis()returns a primitive longnot a object Long.
So you cannot invoke the longValue()method or any method on it as primitive cannot be the object of method invocations.
System.currentTimeMillis()返回一个原语long而不是一个对象Long。因此，您不能调用该longValue()方法或其上的任何方法，因为原语不能是方法调用的对象。
Besides, it is useless to invoke longValue()as System.currentTimeMillis() returns already a long value.
此外，longValue()因为 System.currentTimeMillis() 已经返回一个 long 值，所以调用它是没有用的。
This is better :
这个更好 ：
if(System.currentTimeMillis()==finish){
But in fact this condition : if(System.currentTimeMillis()==finish)could not be trueeven if System.currentTimeMillis() == finishin the whilestatement :
但事实上，这个条件： if(System.currentTimeMillis()==finish)不能true即使 System.currentTimeMillis() == finish在while语句：
while (found<3 && System.currentTimeMillis() < finish) {
Command command = parser.getCommand();
processCommand(command);
}
Because between the end of the while statement and the condition evaluation :
因为在 while 语句的结尾和条件评估之间：
if(System.currentTimeMillis() == finish), the time goes on elapsing.
if(System.currentTimeMillis() == finish)，时间在流逝。
So you should rather use :
所以你应该使用：
if(System.currentTimeMillis() >= finish){
