Java Basic Input and Output

In this blog, we will be discussing about how we take input from the user and how the output is displayed in java.

Java Input

There are different ways to take input from user in java. But in this blog, we will talk about taking input from user using the object of Scanner class.

In order to use the object of Scanner class, we need to import java.util.Scanner package. 

import java.util.Scanner;

Then we create an object of Scanner class. An object is an instance of a class in java. We can use the object to take input from the user:

// creating an object of Scanner class

Scanner input = new Scanner(System.in);

// taking input from the user

int number = input.nextInt();

Example: Get Integer Input From the User

import java.util.Scanner;

class Input {

    public static void main(String[] args) {

       

        Scanner input = new Scanner(System.in);

       

        System.out.print("Enter an integer: ");

        int number = input.nextInt();

        System.out.println("You entered " + number);

    }

}

Output

Enter an integer: 23

You entered 23

In the above example, we have created an object named input of the Scanner class. We then call the nextInt() method of the Scanner class to get an integer input from the user.

Similarly, we can use nextLong(), nextFloat(), nextDouble(), and next() methods to get long, float, double, and string input respectively from the user.

Note: We have used the close() method to close the object. It is recommended to close the scanner object once the input is taken.

Example: Get float, double and String Input

import java.util.Scanner;

class Input {

    public static void main(String[] args) {

       

        Scanner input = new Scanner(System.in);

       

        // Getting float input

        System.out.print("Enter float: ");

        float myFloat = input.nextFloat();

        System.out.println("Float entered = " + myFloat);

       

        // Getting double input

        System.out.print("Enter double: ");

        double myDouble = input.nextDouble();

        System.out.println("Double entered = " + myDouble);

       

        // Getting String input

        System.out.print("Enter text: ");

        String myString = input.next();

        System.out.println("Text entered = " + myString);

    }

}

Output

Enter float: 2.343

Float entered = 2.343

Enter double: -23.4

Double entered = -23.4

Enter text: Hey!

Text entered = Hey!

As mentioned, there are other several ways to get input from the user. To learn more about Scanner, visit Java Scanner.

Java Output

In java, for displaying output, you can simply use

System.out.println(); or

System.out.print(); or

System.out.printf();

to send the output to the standard output(screen) ===> Standard Output Stream Object

Here,

• System is a class.
• out is a public static field: it accepts output data.

Let's take an example to print a statement

class PrintOutput {

    public static void main(String[] args) {

       

        System.out.println("Java programming is interesting.");  

    }

}

Output

Java programming is interesting.

Here we have used println() method for displaying the string. To learn about println() method, visit Chapter 1 Question 2.1

Difference between println(), print() and printf()

• print() - It prints string inside the double quotes " ".
• println() - It prints string inside the quotes similar like print() method. Then the cursor moves to the beginning of the next line.
• printf() - It provides string formatting (used for formatting the display/output).

Example: print() and println()

class Output {

    public static void main(String[] args) {

       

        System.out.println("1. println ");

        System.out.println("2. println ");

       

        System.out.print("1. print ");

        System.out.print("2. print");

    }

}

Output

1. println

2. println

1. print 2. print

In the above example, we have shown the working of the print() and println() methods. To learn about the printf() method, visit Java printf().

Example: Printing Variables and Literals

class Variables {

    public static void main(String[] args) {

       

        Double number = -10.6;

       

        System.out.println(5);

        System.out.println(number);

    }

}

Output

5

-10.6

Here, you can see that we have not used the quotation marks. It is because to display integers, variables and so on, we don't use quotation marks.

Example: Print Concatenated Strings

class PrintConcatenatedStrings {

    public static void main(String[] args) {

       

        Double number = -10.6;

       

        System.out.println("I am " + "awesome.");

        System.out.println("Number = " + number);

    }

}

Output

I am awesome.

Number = -10.6

In the above example, notice the line,

System.out.println("I am " + "awesome.");

Here, we have used the + operator to concatenate (join) the two strings: "I am " and "awesome.".

And also, the line,

System.out.println("Number = " + number);

Here, first the value of variable number is evaluated. Then, the value is concatenated to the string: "Number = ".