Hello everybody,
It’s Michael, and today’s post will be on user input, importing classes, and doing math in Java. I know these may seem like three totally unrelated topics, but I think they relate well to one another, which is why I’m going to cover all of them in this post.
First off, let’s discuss how to manage user input in your Java program. If you weren’t already aware, Java output doesn’t always have to be predefined-you can write your code so that you can choose the output.
The first thing you would need to do is import the Scanner class from Java, which is the class that handles all text input (don’t think about using it for graphics-heavy programs). Importing the Scanner class (or any class for that matter) allows you to use all its methods.
Here’s an example of a Scanner program:
The first thing I did was to import the Scanner class. I then created s, which is a variable of type Scanner. Remember to always create a Scanner variable every time you want to use the Scanner class in your program! And remember to ALWAYS set the parameters as (System.in).
I then used System.out.println to write the command asking the user for their input. The user’s input then is stored in a variable, in this case int year. You must always store your input in a variable if you want it to display on the screen. What variable type you choose depends on what kind of input you are seeking. In this case, since I am seeking integers, I want to use type int. The value you assign to the variable would be (name of Scanner variable).next(type of variable your input is). Since my Scanner variable is named s and my input variable is of type int, the value I assigned my variable was s.nextInt(). The next______ method you use depends on the input variable’s type, so if I had a char variable I would use s.nextChar(). Please note that there is no nextString method so for String variables use next or nextLine.
For those who would like a video demonstration of the Scanner class, check out this program-Scanner demo.
Now, Scanner isn’t the only class you can import from Java. In fact there are plenty of other classes (and methods) you can use and import for a variety of purposes, such as the class Calendar for calendar programs. The best part is that you don’t need to memorize all of the classes available on Java, as there is a handy online dictionary where you can look up classes and methods that you need for your program. This dictionary does a very good job of explaining how you can use each available class.
Now at the beginning of this post, I said I was going to cover how to do math in Java. Well, there is a certain class that I will show you how to use to do just that-it’s the Math class. To access this class, use the line import java.lang.Math. Here are three programs utilizing the Math class and its methods.
This program asks the user for a negative number, then finds the absolute value of that number. Since I typed -33, the program calculated 33 as the absolute value.
This program asks the user for two numbers, then will calculate the value of the first number raised to the power of the second number. Since my first number was 9 and my second number was 3, the program printed out 729, or 9 cubed (which is a more colloquial way of saying “to the third power”)
This last program asks the user for a number, which in this context is an angle measurement for a right triangle. The program will then display the cosine (recall SOHCAHTOA) for that angle measurement; since I used a 49 degree angle in this example, the cosine is 0.3006 (rounded to four decimal places).
However, one thing to note is that the Math is more geared towards complex mathematical operations (like finding logs, trigonometric ratios, and square roots). You don’t need the Math class for basic arithmetic.
In case you’re wondering, here are two programs showing how to do basic arithmetic in Java:
This program demonstrates simple division; the user is asked for a number divisible by 3, then the program will print out the quotient of that number divided by 3. Since I used 612, the quotient displayed was 204.
This program utilizes the order of operations (think PEMDAS); the user is asked to type in a number and the program will print out the answer to the problem (pemdas/2)*3+8-4. Remember pemdas is the name of the variable where you will store the number you choose. I chose to store the user input as a double because I wanted a precise answer; had I stored the input as int , I would’ve gotten the nearest whole number (12) instead of the more precise answer I wanted-11.5.
- Something I should have pointed out earlier-ALWAYS remember to put semicolons after each statement! To be clear, this only means the lines of code inside each method or class along with any import statements. This doesn’t mean semicolons are needed after class/method declarations themselves!
- This isn’t totally necessary when coding, but the
//symbol right before a line of code is a way to take notes within your program. The compiler won’t read any line of code that begins with//.
Now before I go, here’s a video demonstration on doing math in Java (both with the Math class and without)-Java Math.
Thanks for reading,
Michael