05 Java Fundamentals

Input in Java

By Dummy for Dummies

Input in Java

What happens when Monkey collects food for the whole jungle? Monkey grabs bananas. Just bananas. Don't be like Monkey.

A good program works for everyone, not just the one case you had in mind. But you don't have everyone's data ahead of time, their name, age, whatever it is. So instead, you ask for it while the program is running. That's input.

How to Take Input?

There are several ways to take input from the user. The easiest and most common is the Scanner class.

Java doesn't load every feature by default, you pull in only what you need, when you need it. That keeps things light. Scanner is one of those features, and you bring it in with one line:

import java.util.Scanner;

This tells Java to pull Scanner in from its utilities so you can actually use it. But wait, what is a class? How do you use one? Let's talk about that.

Class

Monkey sees a photo of a banana. Monkey cannot eat the photo. But the photo shows the shape and color, everything a real banana should have.

A class works the same way, it's a blueprint. On its own you can't do anything with it. But unlike the banana photo, a class lets you build a real, usable thing from it, called an object. We already imported the class. Now let's create an object from it:

Creating Scanner Object

import java.util.Scanner;

public class InputInt {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);  // This line created object
    }
}

The line which created the object says to the computer: "Hey Mr. Scanner, create a new Scanner object that takes input into the system and name it sc."

Points to Remember

• Class is just a blueprint Scanner
• Every class name starts with a capital letter; object name must NOT start with a capital letter
• Class is imported at the top of the code even before the greyed lines
• Object is created after the line with main keyword
• We will use the object, e.g., sc
• You can give any name to the object, e.g., input or scanner or scnnrrr
• The object name must not be exactly the same as the class name (Scanner and scanner are different)
• Repeat the same process and exact code every time you want to create a Scanner object

Taking Input from User

As we know there are many types of variables and many datatypes. Therefore taking input for each is a bit different. Here is a list for each:

Let's write a simple code for it... The green part beginning with // are comments we talked about earlier. We are putting them to work to explain the code, and the computer will ignore them while the remaining will be read.

// importing Scanner
import java.util.Scanner;

// Start of the program
public class Main {
    public static void main(String[] args) {
        // creating Scanner object
        Scanner sc = new Scanner(System.in);

        // Integer input
        System.out.print("Enter your age: ");
        int age = sc.nextInt();

        // Double input
        System.out.print("Enter your GPA: ");
        double gpa = sc.nextDouble();

        // Word input
        System.out.print("Enter your first name: ");
        String firstName = sc.next();

        sc.nextLine();  // Consumes the leftover newline

        // Full line input
        System.out.print("Enter your full address: ");
        String address = sc.nextLine();

        // Character input
        System.out.print("Enter your grade (A/B/C...): ");
        char grade = sc.next().charAt(0);

        // Display results
        System.out.println(age);
        System.out.println(gpa);
        System.out.println(firstName);
        System.out.println(address);
        System.out.println(grade);
    }
}

Closing

That's it for taking input in Java! By using the Scanner, we can collect numbers, words, sentences, and even single characters right from the keyboard. In the next blog, we will learn how to give output back to the user.