Scanner Buffer / CRLF Problem

Workbook 1c, pp. 82-86 — Why nextInt() and nextLine() don't play nice

Buggy Code

          Scanner scanner = new Scanner(System.in);
          System.out.println("Enter your age: ");
          int age = scanner.nextInt();
          System.out.println("Enter your name: ");
          String name = scanner.nextLine();
          System.out.println("Hello " + name + ", age " + age);
        

age ?

name ?

Input Buffer

System.in buffer

Press Next Step to walk through the code line by line.

Console Output

Waiting...

Fixed Code

          Scanner scanner = new Scanner(System.in);
          System.out.println("Enter your age: ");
          int age = scanner.nextInt();
          scanner.nextLine(); // consume the leftover \n
          System.out.println("Enter your name: ");
          String name = scanner.nextLine();
          System.out.println("Hello " + name + ", age " + age);
        

age ?

name ?

Input Buffer

System.in buffer

Press Next Step to see how the fix works.

Console Output

Waiting...

⚠ The Golden Rule

After nextInt(), nextDouble(), or nextFloat(), always add an extra scanner.nextLine() to consume the leftover newline character before reading a String.

★ Alternative Approach

Some developers avoid this problem entirely by reading everything as strings with nextLine() and parsing numbers manually with Integer.parseInt() or Double.parseDouble().

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