Arithmetic Operators and Data Types

Learn about the arithmetic operators and data types in Java.

We'll cover the following

Back to our project

So far, we’ve covered good ground in learning how to code for some of the project requirements. Let’s take a look at our client’s requirements once again.

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Project requirements that require printing on the screen
Project requirements that require printing on the screen

According to requirements 4 and 6, our app should be able to:

  • Perform calculations of addition, subtraction, multiplication, and division.

  • Compute the actual answer to each question.

So, let’s dive right in!

Adding two numbers

This should be easy: input two numbers and assign them to num1 and num2, then print num1 + num2. Run the program below and see if we’re getting the expected outputInput 8 and 2. What should be the expected output of 8 + 2?. Let’s enter “8” as the first number and “2” as the second one. Run the program below and see if we’re getting the expected output.

import java.util.Scanner;

public class MyJavaApp {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //Taking two numbers as input and storing inside two variables respectively
        System.out.print("First number: ");
        String num1 = scan.nextLine();
        System.out.print("Second number: ");
        String num2 = scan.nextLine();
        System.out.println("The answer to " + num1 + " + " + num2 + " is " + num1 + num2);
        
 }
}
Program to add two numbers

But wait a minute! We get the output “82” instead of “10.” Why do you think that is?

Data types and their conversion

In our code:

  1. When we use scan.nextLine(), it takes whatever we type and returns us a string. So, the numbers stored in num1 and num2 are treated as text and not as mathematical numbers.

In Java, String is a basic data type used to represent text or sequences of characters (string). It’s employed for storing and manipulating words, sentences, or any textual information in a program. Strings are enclosed in double quotes " ".

  1. When we try to add num1 and num2 using the + operator, it concatenatesThis is the action of joining or linking strings together to create a longer string. the two strings rather than adding the numbers. That’s why we got “82” instead of “10.”

To solve this problem, we need to convert these strings to numbers (to another basic data type called integer), so the computer understands that we want to do math with them.

An integer is a whole number, either positive or negative, without any decimal or fractional parts.

If there was a way to convert the input strings to integers while we were scanning for input, perhaps we could add the two numbers easily using a +. And there is one such method we can invoke: scan.nextInt().

The int data type

When we know that our variable will store integers instead of a string, we have to define it as such. Two things happen in line 8. First, we tell Java that num1 is an integer and we initialize it with the input coming from the keyboard, but instead of calling nextLine(), we call scan.nextInt(). Read the code carefully, line by line. It will make sense to you.

import java.util.Scanner;

public class MyJavaApp {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //Taking two numbers as input and storing inside two variables respectively
        System.out.print("First number: ");
        int num1 = scan.nextInt();
        System.out.print("Second number: ");
        int num2 = scan.nextInt();
        int result = num1 + num2;
        System.out.println("The answer to " + num1 + " + " + num2 + " is " + result);
    }
}
Program to add two numbers

Running the code above gives us “10”—which is the result we were expecting.

It’s always a good idea to convert the input from the keyboard to int in the case of numbers.

Adding arithmetic operations

Now that we’ve covered the concepts of basic data types, like int and String, and how to convert each data type to another, let’s get back to our project requirements. This brings us to the arithmetic operators.

The arithmetic operators in Java

In Java, arithmetic operators are special symbols that perform operations on variables and values, just like when solving simple arithmetic equations. For numbers, we’ve already seen how the + operator adds two numbers together. Other arithmetic operators available in Java are - for subtraction, * for multiplication, and / for division.

Let’s look at an example of each operator in use.

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public class MyJavaApp {
    public static void main(String[] args) {
        int num1 = 7;
        int num2 = 3;
        
        // addition
        System.out.println("7 + 3 is " + (num1 + num2));
        // subtraction
        System.out.println("7 - 3 is " + (num1 - num2));
        // multiplication
        System.out.println("7 * 3 is " + (num1 * num2));
        // division
        System.out.println("7 / 3 is " + (num1 / num2));
    }
}

Now, after running the program above, you might have noticed that we’re not getting the last output as a fractional value, even though 7 / 3 is not a whole number. This is because in Java, when two integers are divided using / operator, the result is also an integer—in this case, 2. But in actuality, the answer is more like 2.333, which is not an integer.

Just like we have an int data type for whole numbers, we also have a basic data type for numbers with decimal values (such as 2.333) known as double. So, when we know that a variable will be assigned such kind of value, we should declare a double, which is what we do with the variable named result in line 3 below:

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public class MyJavaApp {
    public static void main(String[] args) {
        double result = 2.333;
        System.out.println(result);
    }
}

Now that we know we have operators available in Java, we can easily compute the correct answer for each question.

In the program below, let’s take the user’s answer and then print its correct answer (calculated by our program). 

import java.util.Scanner;

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

        int n1 = 4;
        int n2 = 9;

        String question = "What is " + n1 + " + " + n2 + "?"; 
        System.out.println(question);
        int userAnswer = scan.nextInt();
        System.out.println("Your answer is: "+ userAnswer);
        // Computing the correct answer
        System.out.println("The correct answer is: " + (n1 + n2));
        
 }
}
Printing the user’s answer and the correct answer

We can do the same for all operators, as shown below:

import java.util.Scanner;

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

        int n1 = 4;
        int n2 = 9;
        int userAnswer;

        String question = "What is " + n1 + " + " + n2 + "? "; 
        System.out.print(question);
        userAnswer = scan.nextInt();
        System.out.println("Your answer is: "+ userAnswer);
        // Computing the correct answer
        System.out.println("The correct answer is: " + (n1 + n2));
        
        question = "What is " + n1 + " - " + n2 + "? "; 
        System.out.print(question);
        userAnswer = scan.nextInt();
        System.out.println("Your answer is: "+ userAnswer);
        // Computing the correct answer
        System.out.println("The correct answer is: " + (n1 - n2));

        question = "What is " + n1 + " * " + n2 + "? "; 
        System.out.print(question);
        userAnswer = scan.nextInt();
        System.out.println("Your answer is: "+ userAnswer);
        // Computing the correct answer
        System.out.println("The correct answer is: " + (n1 * n2));

        question = "What is " + n1 + " / " + n2 + "? "; 
        System.out.print(question);
        userAnswer = scan.nextInt();
        System.out.println("Your answer is: "+ userAnswer);
        // Computing the correct answer
        System.out.println("The correct answer is: " + (n1 / n2));        
 }
}
Printing the user’s answer and the correct answer for different arithmetic operations

That’s it! We’ve learned to incorporate requirements 4 and 6.

Review of the lesson

To sum up, we learned some of the methods and data types in Java that made it possible for us to compute correct sums. You might be thinking that Java has a built-in method for every situation in the world. However, that’s not true, and it’s a good thing too.