Non-terminating Java program

问题

I have this Java input-related problem. I'm solving some cases in UVAToolkit, but there are some problems that the line input requires from the System.in. Basing from these codes below, how could I terminate the problem once I've pressed key? The sample input/output are displayed below.

Scanner scanner = new Scanner(System.in);
String line;
while((line = scanner.nextLine()) != null) {
    System.out.println(line);
}
System.out.println("done");

Sample Input:

1 10
10 100
100 1000

Sample Output:

Thanks in advance.

回答1:

Don't check for null input but for an empty string. This way, you should be able to terminate just by pressing the return key.

while(!(line = scanner.nextLine()).equals(""))

回答2:

To end the input, you should pree ctrl+d, otherwise, scanner.nextLine() will not return null, but hang.

if you want to quit the application once the word quit entered for example, you can do:

Scanner scanner = new Scanner(System.in);
String line;
while((line = scanner.nextLine()) != null && !line.equalsIgnoreCase("quit")) {
    System.out.println(line);
}
System.out.println("done");

回答3:

Either use sentinel value like STOP\n or close the stream. Press ctrl +z for windows(i guess) and ctrl + d for Linux to close the stream.

回答4:

You could decide on a special string that will make the loop end, and check for this special string. For example:

while((line = scanner.nextLine()) != null) {
    if (line.equals("quit") break;
    System.out.println(line);
}
System.out.println("done");

回答5:

Try checking for an empty line instead of null:

while((line = scanner.nextLine()).isEmpty()) {
    System.out.println(line);
}

来源：https://stackoverflow.com/questions/8062749/non-terminating-java-program

标签

java

java.util.scanner