Question

I must be missing something obvious about how the various Scanner methods work but this really doesn’t make any sense:

this code causes an infinite loop:

Scanner valueScan = new Scanner(line);
valueScan.useDelimiter(",");
while(valueScan.hasNext())
{
count++;
}

while this code is valid:

Scanner valueScan = new Scanner(line);
valueScan.useDelimiter(",");
while(valueScan.hasNext())
{
System.out.println("value token: " + valueScan.next());
cellCount++;
}

This is from Oracle’s documentation I am not sure if it applies or what it means: “This method may block while waiting for input to scan, even if a previous invocation of hasNext() returned true. ” (http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html#next%28%29)

Answer 1

Because hasNext doesn’t remove anything from the Scanner, so in your first case, you never change its state, hence the infinite loop. next extracts input, and hence changes the state of the Scanner.