User input (Scanner)

String Input

import java.util.Scanner; // import java scanner class
public class UserInput {
	public static void main (String[] args){
		Scanner scanner = new Scanner(System.in); // creating scanner object
		System.out.print("What is Your Name : ");
		String name = scanner.nextLine(); // reading string
 
		System.out.print("Hello " + name);
 
	}
 
}

• import java.util.Scanner; : The Scanner class is a part of Java’s standard library and is used for reading input from various sources, such as the keyboard (standard input).

• public class UserInput { : Define the UserInput class. In Java, all codes must be a contained within a class, and the class name must be match the filename (UserInput.java)

• public static void main (String[] args) { : main method, The main method is the entry point for any Java application.

• Scanner scanner = new Scanner(System.in); : The Scanner is set to read input from System.in, which represents standard input (typically the keyboard).

• String name = scanner.nextLine(); : The nextLine() method of the Scanner object reads the entire line of input that the user enters, This input is stored in the String variable name,The nextLine() method reads everything the user types until they press the Enter key, making it ideal for capturing full lines of text.

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Int Input

import java.util.Scanner;
public class UserInput {
 
public static void main (String[] args){
	Scanner scanner = new Scanner(System.in); // creating scanner object
	System.out.print("What is Your Name : ");
	
	String name = scanner.nextLine(); // reading string
	System.out.println("How old are you : ");
 
	int age = scanner.nextInt(); // reading integer
	System.out.print("Hello " + name);
 
	System.out.println(" you are " + age + " years old");
 
	}
 
}

What if we input string to age variable? that leads to Exception Error saying Exception in thread "main" java.util.InputMismatchException. We will cover Exception Handling later

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Common issue happens after we use nextInt() after nextLine()

import java.util.Scanner;
public class UserInput {
	public static void main (String[] args){
		Scanner scanner = new Scanner(System.in); // creating scanner object
		System.out.print("What is Your Name : ");
		String name = scanner.nextLine(); // reading string
 
		System.out.println("How old are you : ");
		int age = scanner.nextInt(); // reading integer
 
		System.out.println("What is your favorite food : ");
		String food = scanner.nextLine(); // reading string
		
		System.out.print("Hello " + name);
		System.out.println(" you are " + age + " years old");
		System.out.println("Your favorite food is " + food);
 
	}
 
}

What happens here is after we enter our age. input for favourite is going to skip by java. like this :

What happens here is :

What happens when u use nextLine() :

Transclude of User-input-(Scanner)-2024-08-30-00.39.07.excalidraw

But what happens when u use nextInt():

Transclude of User-input-(Scanner)-2024-08-30-00.46.44.excalidraw

FIX 💡

To get rid of this we can place empty scanner.nextLine() method after nextInt() to clear out the scanner

import java.util.Scanner;
public class UserInput {
 
	public static void main (String[] args){
		Scanner scanner = new Scanner(System.in); // creating scanner object
		System.out.print("What is Your Name : ");
		String name = scanner.nextLine(); // reading string
		
		System.out.println("How old are you : ");
		int age = scanner.nextInt(); // reading integer
		
		scanner.nextLine(); // to consume the newline character
		
		System.out.println("What is your favorite food : ");
		String food = scanner.nextLine(); // reading string 
		
		System.out.print("Hello " + name);
		System.out.println(" you are " + age + " years old");
		System.out.println("Your favorite food is " + food);
	}
 
}