User Input in Java

User input is the bridge between a Java program and the real world. Java provides several classes such as Scanner, BufferedReader and Console to read values from the keyboard. Mastering input handling is the very first step toward building interactive command line applications.

• Import the Scanner class with import java.util.Scanner;
• Create a Scanner object: Scanner sc = new Scanner(System.in);
• Use sc.nextInt(), sc.nextLine(), sc.nextDouble() to read values.
• Always close the scanner with sc.close() when done.

Let's start with a hands-on example. The program below shows the core idea behind User Input in just a few lines of Java. Read it line by line and observe how Java executes each statement in order.

import java.util.Scanner;

class Main
{
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int n = sc.nextInt();

        System.out.println("You entered: " + n);

        sc.close();
    }
}

The following examples progress from simple to more practical patterns. Try each in your IDE, change the inputs and observe the output. This is the fastest way to internalize the concept.

import java.util.Scanner;

class Main
{
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter your name: ");
        String name = sc.nextLine();

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

        System.out.println("Hello " + name + ", age " + age);
    }
}

import java.util.Scanner;

class Main
{
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter first number: ");
        int a = sc.nextInt();

        System.out.print("Enter second number: ");
        int b = sc.nextInt();

        int sum = a + b;

        System.out.println("Sum = " + sum);
    }
}

import java.io.*;

class Main
{
    public static void main(String args[]) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        System.out.print("Enter city: ");
        String city = br.readLine();

        System.out.println("City entered: " + city);
    }
}

import java.util.Scanner;

class Main
{
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter price: ");
        double price = sc.nextDouble();

        double tax = price * 0.18;

        System.out.println("Tax = " + tax);
    }
}

• Always call sc.nextLine() after sc.nextInt() if you plan to read a string next — to consume the newline character.
• Closing a Scanner that wraps System.in also closes System.in. Be careful in large programs.
• BufferedReader.readLine() always returns a String — convert manually with Integer.parseInt().
• Use a try-with-resources block to ensure Scanner is closed automatically.
• For password input, prefer System.console().readPassword() over Scanner.

Reading is not enough — practice solidifies knowledge. Try every question below in your own editor before peeking at any solution.

• Q1. Write a program that reads two numbers and prints their product.
• Q2. Read a student's name and three marks, then print the average.
• Q3. Take a sentence as input and print its length using length().
• Q4. Read a temperature in Celsius and convert it to Fahrenheit.
• Q5. Read 5 numbers in a loop and print the largest one.

These are the most common questions asked in Java interviews on this topic. Memorize the concept, not just the answer — interviewers often follow up with edge cases.

Even experienced developers slip on the same pitfalls. Watch out for these classic mistakes while working with User Input in Java:

• Forgetting the semicolon ; at the end of statements while using User Input.
• Mixing up similar method names — read Java docs before using new APIs related to User Input.
• Ignoring compiler warnings — they often hint at bugs that will appear later in production.
• Hard-coding values that should come from configuration files or environment variables.
• Not handling edge cases: empty inputs, very large inputs, negative numbers and null references.
• Skipping unit tests — small tests prevent big regressions, especially around control flow.