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joc
Asked: 2020-09-03 01:45:57 +0800 CST 2020-09-03 01:45:57 +0800 CST

Scanner.nextLine() does not act correctly after Scanner.nextInt()

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I have this code:

Scanner scan = new Scanner(System.in);
    
String s2 = scan.nextLine();
int i2    = scan.nextInt();
    
System.out.println("natural= " + i2);
System.out.println("cadena = " + s2);
    
scan.close();

Which works correctly:

This is a string
1714
natural= 1714
string = This is a string

But if I change the order of the lines of the Scanner:

int i2    = scan.nextInt();
String s2 = scan.nextLine();

It ignores the line scan.nextLine()and gives me the result right after I enter the int.

1714
natural= 1714
chain =

Does anyone know what is going on and how to fix it?

java

1 Answers

  1. Best Answer

    The behavior nextInt()is not what you expect. When you input a 1714you are actually inputting a 1714and a line break ( \n) and the nextInt()does not consume the line break ( \n).

    That means the nextLine()is reading this line break (which is empty --> \n).

    To fix it, when you do a nextInt()always put a nextLine()that will have no content.

    From your code:

    int i2    = scan.nextInt();
String saltoDeLinea = scan.nextLine();
String s2 = scan.nextLine();

    Another way to fix it is to always read with nextLine()and do a castpost:

    int i2 = Integer.parseInt(scan.nextLine());
String s2 = scan.nextLine();

    In this answer from the original SO they give some more detail, in case you are interested.

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