Java Scanner: The Ultimate Beginner’s Guide

Introduction: The Scanner Machine

By default, the variables you write in code are fixed. But what if we want to ask the user for the numbers?

Think of the Scanner like a physical scanner machine in an office. Usually, when you put a paper in a physical scanner, it scans the entire page at once.

In Java, our Scanner is a bit different. It looks at what the user types on the keyboard, but we can be very specific about what to scan. We can tell it: “Only scan the next number (int)” or “Only scan the next decimal point (float).”

The 3 Steps

To use the Scanner, follow these three steps.

Step 1: The Import Line

Java hides the Scanner tool in a specific library. You need to tell Java where to find it. Put this line at the very top of your file.

import java.util.Scanner;

Step 2: Turn on the Scanner

Inside your code (in the main section), you need to write a specific line to set up the scanner.

Note

This line looks a bit complicated with keywords like new and System.in. For now, please just accept this line as a rule. Copy and paste it exactly as it is.

// This line prepares the scanner to read from the keyboard
Scanner input = new Scanner(System.in);

Step 3: Scan the Data

Now, you command the scanner to wait for the user to type something and store it in a variable.

int age = input.nextInt();

Cheat Sheet: Which Command to Use?

Depending on the Data Type (variable) you want to fill, you must use a specific command.

Data Type	Command	Example Use Case
`int`	`input.nextInt()`	Whole numbers (Age, Year)
`long`	`input.nextLong()`	Large whole numbers (Population)
`float`	`input.nextFloat()`	Decimal numbers (Temperature)
`double`	`input.nextDouble()`	Decimal numbers (Price, GPA)
`boolean`	`input.nextBoolean()`	True/False answers

💻 Full Code Example

Here is a complete program. It asks for a student’s number and age.

import java.util.Scanner; // Step 1

public class Main {
    public static void main(String[] args) {
    
        // Step 2: Setup the Scanner 
        // (Remember: Just copy this line for now!)
        Scanner input = new Scanner(System.in);

        // Step 3: Ask and Scan
        
        // 1. Ask for an Integer
        System.out.print("Enter your Student Number: ");
        int studentNumber = input.nextInt();

        // 2. Ask for an Integer
        System.out.print("Enter your age: ");
        int age = input.nextInt();

        // Print the results back to see if it worked
        System.out.println("--- Result ---");
        System.out.println("Student Number: " + studentNumber);
        System.out.println("Age: " + age);
    }
}

Summary

Import the tool at the top: import java.util.Scanner;
Setup the tool inside main: Scanner input = new Scanner(System.in);
Scan the specific type you need: nextInt() or nextDouble().

Happy Coding! 🚀