如何让 Java 注册一个带空格的字符串输入？

Question

Here is my code:

public static void main(String[] args) {
  Scanner in = new Scanner(System.in);
  String question;
  question = in.next();

  if (question.equalsIgnoreCase("howdoyoulikeschool?") )
    /* it seems strings do not allow for spaces */
    System.out.println("CLOSED!!");
  else
    System.out.println("Que?");

When I try to write "how do you like school?" the answer is always "Que?" but it works fine as "howdoyoulikeschool?"

Should I define the input as something other than String?

Answer 1

in.next() will return space-delimited strings. Use in.nextLine() if you want to read the whole line. After reading the string, use question = question.replaceAll("\\\\s","") to remove spaces.

Answer 2

Since it's a long time and people keep suggesting to use Scanner#nextLine() , there's another chance that Scanner can take spaces included in input.

Class Scanner

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace.

You can use Scanner#useDelimiter() to change the delimiter of Scanner to another pattern such as a line feed or something else.

Scanner in = new Scanner(System.in);
in.useDelimiter("\n"); // use LF as the delimiter
String question;

System.out.println("Please input question:");
question = in.next();

// TODO do something with your input such as removing spaces...

if (question.equalsIgnoreCase("howdoyoulikeschool?") )
    /* it seems strings do not allow for spaces */
    System.out.println("CLOSED!!");
else
    System.out.println("Que?");

Answer 3

I found a very weird thing in Java today, so it goes like -

If you are inputting more than 1 thing from the user , say

Scanner sc = new Scanner(System.in);
int i = sc.nextInt();
double d = sc.nextDouble();
String s = sc.nextLine();

System.out.println(i);
System.out.println(d);
System.out.println(s);

So, it might look like if we run this program, it will ask for these 3 inputs and say our input values are 10, 2.5, "Welcome to java" The program should print these 3 values as it is, as we have used nextLine() so it shouldn't ignore the text after spaces that we have entered in our variable s

But, the output that you will get is -

10
2.5

And that's it, it doesn't even prompt for the String input. Now I was reading about it and to be very honest there are still some gaps in my understanding, all I could figure out was after taking the int input and then the double input when we press enter, it considers that as the prompt and ignores the nextLine().

So changing my code to something like this -

Scanner sc = new Scanner(System.in);
int i = sc.nextInt();
double d = sc.nextDouble();
sc.nextLine();
String s = sc.nextLine();

System.out.println(i);
System.out.println(d);
System.out.println(s);

does the job perfectly, so it is related to something like "\\n" being stored in the keyboard buffer in the previous example which we can bypass using this.

Please if anybody knows help me with an explanation for this.

Answer 4

Instead of

Scanner in = new Scanner(System.in);
String question;
question = in.next();

Type in

Scanner in = new Scanner(System.in);
String question;
question = in.nextLine();

This should be able to take spaces as input.

Answer 5

This is a sample implementation of taking input in java, I added some fault tolerance on just the salary field to show how it's done. If you notice, you also have to close the input stream .. Enjoy :-)

/* AUTHOR: MIKEQ
 * DATE: 04/29/2016
 * DESCRIPTION: Take input with Java using Scanner Class, Wow, stunningly fun. :-) 
 * Added example of error check on salary input.
 * TESTED: Eclipse Java EE IDE for Web Developers. Version: Mars.2 Release (4.5.2) 
 */

import java.util.Scanner;

public class userInputVersion1 {

    public static void main(String[] args) {

    System.out.println("** Taking in User input **");

    Scanner input = new Scanner(System.in);
    System.out.println("Please enter your name : ");
    String s = input.nextLine(); // getting a String value (full line)
    //String s = input.next(); // getting a String value (issues with spaces in line)

    System.out.println("Please enter your age : ");
    int i = input.nextInt(); // getting an integer

    // version with Fault Tolerance:
    System.out.println("Please enter your salary : ");
    while (!input.hasNextDouble())
    {
        System.out.println("Invalid input\n Type the double-type number:");
        input.next();
    }
    double d = input.nextDouble();    // need to check the data type?

    System.out.printf("\nName %s" +
            "\nAge: %d" +
            "\nSalary: %f\n", s, i, d);

    // close the scanner
    System.out.println("Closing Scanner...");
    input.close();
    System.out.println("Scanner Closed.");      
}
}