How To Check If Scanner Has Input Before Scanning Next

Question

I am trying to check if my scanner has multiple tokens before separating the tokens. I am currently trying to use scanner.hasNext() (my scanner's name is sc). If the user inputs "string int int" then I don't want to print "enter age" or "enter grade"

System.out.println("Enter name or command: ");
            name = sc.next();
            if(name.toLowerCase().equals("next")) {
                students.remove(0);
            }else if(name.toLowerCase().equals("end")) {
                running = false;
            }else {
//This is where it gets dicey
                if(!sc.hasNext())
                    System.out.println("Enter age: ");
                age = sc.nextInt();
                if(!sc.hasNext())
                    System.out.println("Enter grade: ");
                grade = sc.nextInt();

                if(first) {
                    students.add(new Student(name, age, grade));
                    first = false;
                }else {
                    addStudent(new Student(name, age, grade), students.get(students.size()-1));
                }
            }

Currently, my program skips past the if statements no matter the input. If I remove the !s then the lines print no matter what, even if input is a single line. They also seem to print after the nextInt is taken which I found to be odd. I would be very grateful for some help!

Answer 1

I had to make some modifications, as it wouldn't compile. When i ran it, it gave me what you're saying you want to have:

C:\Users\..snip..\stackOverflow>java src\stackOverflowTest.java
Enter name or command:
Peter 78 34
addStudent(new Student(name, age, grade), students.get(students.size()-1));

However, if I only put in one parameter, it just hangs (in accordance to the javaDoc: "This method may block while waiting for input to scan."):

C:\Users\..snip..\stackOverflow>java src\stackOverflowTest.java
Enter name or command:
hello

This is the compilable modification:

import java.util.Scanner;

public class StackOverflowTest {
  static String name;
  static int age;
  static int grade;
  static boolean first;
  static boolean running;

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter name or command: ");
      name = sc.next();
      if(name.toLowerCase().equals("next")) {
            System.out.println("students.remove(0);");
//          students.remove(0);
      }else if(name.toLowerCase().equals("end")) {
          running = false;
      }else {

//This is where it gets dicey
        if(!sc.hasNext())
            System.out.println("Enter age: ");
        age = sc.nextInt();
        if(!sc.hasNext())
            System.out.println("Enter grade: ");
        grade = sc.nextInt();

        if(first) {
            System.out.println("students.add(new Student(name, age, grade));");
//            students.add(new Student(name, age, grade));
            first = false;
        }else {
            System.out.println("addStudent(new Student(name, age, grade), students.get(students.size()-1));");
//            addStudent(new Student(name, age, grade), students.get(students.size()-1));
        }
      }
  }
}

If you want to keep all options open, you may do something like this (note there's no exception handling here):

import java.util.Scanner;

public class StackOverflowTest {
  static String name = "";
  static int age = -1;
  static int grade = -1;

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter name or command: ");


    String[] input = sc.nextLine().split(" ");
    switch (input.length) {
      case 3: grade = Integer.valueOf(input[2]);
              // fallthrough
      case 2: age = Integer.valueOf(input[1]);
              // fallthrough
      case 1: name = input[0];
    };

    if (name.isEmpty()) {
      System.out.println("Enter name: ");
      name = sc.next();
    }   

    if (age == -1) {
      System.out.println("Enter age: ");
      age = sc.nextInt();
    }   

    if (grade == -1) {
      System.out.println("Enter grade: ");
      grade = sc.nextInt();
    }
  }
}