Start learning with our library of video tutorials taught by experts. Get started

Java Essential Training

Creating a simple calculator application


From:

Java Essential Training

with David Gassner

Video: Creating a simple calculator application

It's time to put some of what we've talked about to work in a real application. This is going to be a very tiny almost trivial application that does little bit of calculation. It will accept input from the command line and then evaluate values that the user types in as numbers and add them together, not too complicated, but it will require setting variables, converting values, and doing a few other things that I have taught how to do in this chapter. I'm working in a project named SimpleCalc that's available in the Exercise Files. The calculative class in this project has a main method that in turn makes a call to a method called getInput, the getInput method is down here, the purpose of getInput method is to allow the user to type a value in and then return it as a string.
Expand all | Collapse all
  1. 10m 8s
    1. Welcome
      1m 3s
    2. Is this course for you?
      5m 35s
    3. Using the exercise files
      3m 30s
  2. 31m 24s
    1. The history of Java
      5m 19s
    2. Java compilation and syntax
      8m 54s
    3. Understanding the principles of Java
      8m 28s
    4. Choosing a development environment
      8m 43s
  3. 19m 5s
    1. Installing Java on Windows
      6m 42s
    2. Installing Eclipse on Windows
      3m 19s
    3. Exploring Java on Mac OS X Leopard and Snow Leopard
      2m 27s
    4. Installing Java on Mac OS X Lion
      3m 27s
    5. Installing Eclipse on Mac OS X
      3m 10s
  4. 46m 10s
    1. Creating a Hello World application
      11m 7s
    2. Exploring the Eclipse IDE
      8m 55s
    3. Compiling and running from the command line
      8m 2s
    4. Passing arguments to the application
      8m 17s
    5. Using the Java API documentation
      4m 5s
    6. Memory management and garbage collection
      5m 44s
  5. 58m 57s
    1. Everything is an object
      5m 59s
    2. Declaring and initializing variables
      9m 15s
    3. Working with numbers
      8m 32s
    4. Converting numeric values
      6m 40s
    5. Understanding operators
      7m 58s
    6. Working with character values
      5m 14s
    7. Working with boolean values
      5m 13s
    8. Outputting primitive values as strings
      5m 33s
    9. Creating a simple calculator application
      4m 33s
  6. 53m 40s
    1. Writing conditional code
      5m 35s
    2. Using the switch statement
      8m 50s
    3. Repeating code blocks with loops
      7m 35s
    4. Creating reusable code with methods
      6m 31s
    5. Declaring methods with arguments
      5m 41s
    6. Overloading method names with different signatures
      5m 53s
    7. Passing arguments by reference or by value
      5m 35s
    8. Creating a more complex calculator application
      8m 0s
  7. 20m 30s
    1. Using the String class
      5m 44s
    2. Building strings with StringBuilder
      3m 34s
    3. Parsing string values
      3m 19s
    4. Working with date values
      7m 53s
  8. 20m 44s
    1. Understanding compile-time vs. runtime errors
      4m 5s
    2. Handling exceptions with try/catch
      4m 55s
    3. Throwing exceptions in methods
      2m 50s
    4. Using the debugger
      8m 54s
  9. 32m 22s
    1. Using simple arrays
      4m 47s
    2. Using two-dimensional arrays
      6m 17s
    3. Managing resizable arrays with ArrayList
      7m 14s
    4. Managing unordered data with HashMap
      6m 5s
    5. Looping through collections with iterators
      7m 59s
  10. 52m 2s
    1. Understanding encapsulation
      5m 59s
    2. Creating and instantiating custom classes
      8m 8s
    3. Organizing classes with packages
      6m 47s
    4. Creating and using instance methods
      6m 52s
    5. Storing data in instance variables
      6m 56s
    6. Using constructor methods
      5m 40s
    7. Managing instance data with getter and setter methods
      8m 26s
    8. Using class variables and Enum classes
      3m 14s
  11. 41m 15s
    1. Understanding inheritance and polymorphism
      9m 12s
    2. Extending custom classes
      9m 1s
    3. Overriding superclass methods
      3m 8s
    4. Casting subclass objects
      5m 3s
    5. Understanding interfaces and implementing classes
      4m 2s
    6. Creating your own interfaces
      4m 14s
    7. Using abstract classes and methods
      6m 35s
  12. 32m 17s
    1. Managing files with the core class library
      7m 46s
    2. Managing files with Apache Commons FileUtils
      7m 32s
    3. Reading a text file from a networked resource
      7m 52s
    4. Parsing an XML file with DOM
      9m 7s
  13. 17m 39s
    1. Creating your own JAR files
      4m 54s
    2. Understanding the classpath
      5m 2s
    3. Documenting code with Javadoc
      7m 43s
  14. 47s
    1. Goodbye
      47s

Watch this entire course now—plus get access to every course in the library. Each course includes high-quality videos taught by expert instructors.

Become a member
Please wait...
Java Essential Training
7h 17m Beginner Dec 14, 2011

Viewers: in countries Watching now:

Join author David Gassner as he explores Java SE (Standard Edition), the language used to build mobile apps for Android devices, enterprise server applications, and more. This course demonstrates how to install both Java and the Eclipse IDE and dives into the particulars of programming. The course also explains the fundamentals of Java, from creating simple variables, assigning values, and declaring methods to working with strings, arrays, and subclasses; reading and writing to text files; and implementing object oriented programming concepts.

Topics include:
  • Understanding the history and principles of Java
  • Installing Eclipse and Java
  • Compiling and running from the command line
  • Managing memory and performing garbage collection
  • Declaring and initializing variables
  • Writing conditional code
  • Building and parsing strings
  • Debugging and exception handling
  • Using simple arrays
  • Creating custom classes
  • Working with encapsulation, inheritance, and polymorphism
  • Managing files
  • Documenting code with Javadocs
Subjects:
Developer Programming Languages
Software:
Android Java Eclipse
Author:
David Gassner

Creating a simple calculator application

It's time to put some of what we've talked about to work in a real application. This is going to be a very tiny almost trivial application that does little bit of calculation. It will accept input from the command line and then evaluate values that the user types in as numbers and add them together, not too complicated, but it will require setting variables, converting values, and doing a few other things that I have taught how to do in this chapter. I'm working in a project named SimpleCalc that's available in the Exercise Files. The calculative class in this project has a main method that in turn makes a call to a method called getInput, the getInput method is down here, the purpose of getInput method is to allow the user to type a value in and then return it as a string.

I'm not going to talk right now about the different classes that are used, the BufferedReader and the InputStreamReader, and in fact, for this lesson I'm recommending using this method as a bit of black box. Just call the method knowing you'll get back a String value and to make things less complicated I'm going to collapse the code by clicking on the little minus icon right next to the method name. And that leaves me with a very small view of my code showing the details of the main method. and the fact that there is a getInput method that returns a String. The application in its current state calls the getInput method once and returns the value as a variable called s1 and then outputs that value to the console.

I'll run the application. The value I pass into the method enter a value is displayed as a prompt, I'll type in a value, some value and press Enter and that value is echoed to the console. So I know that the input method is working correctly. Now the goal of this application is to receive two numeric values, so I'm going to change the prompt on this first call to getInput and I'll change the prompt to Enter a numeric value, then I'm going to copy and paste that line of code and I'll change the variable that's being returned to s2.

I don't need this output for the moment so I'm just going to commented out by pressing Ctrl+/ on Windows or Command+/ on Mac. Now the next step is to convert these Strings to numeric values, I want my two Strings to turn into two double values. So I'm going to declare a double value called d1 and I'm going to convert the String to a double value using this method of the double wrapper class, Double.parseDouble and I'll parse in s1. Then I'll do the same thing for the second value double d2= Double.parsedouble(s2).

And so now I have two numeric values. Now I'm going to add the two values together, I'll create a third double value called result and now add d1+d2; Now because I cast the numeric values as doubles originally, they'll correctly add together and create a third double. And then finally, I'll uncomment this command, System.out.println and I'll change the output to "The answer is" and I'll append result. So now I'm asking the user to enter a two values both numbers as long as they can be parsed as double values, the mathematical operation should work.

I'll run the application; I'll click into the console and type in an initial value of 10 and a second value of 25.5. I'm using a fractional value because I know I cast these values as doubles and they can accept that. I'll press Enter and there is the result, The answer is 35.5.Now, let's take a look at what happens if the user types in a non-numeric value, I'll click the Run button again and this time I'll type in a value of xyz. So far so good nothing bad is happened and that's because I haven't tried to parse the String as a number yet, I've just gone to the next line that asks for another String, so I'll type abc, now when I press Enter the parsing will begin and I'll get an error, because xyz can't be translated as a numeric value, specifically as a double value, I get an exception called java.lang.NumberFormatException.

Now, I haven't shown you the tools you need to handle this exception yet, so for now this simple calculative will only work if the user types in correct values, that is String values that can be parsed and turned into numbers without creating exceptions, but if the users does what they are supposed to do directly, then the application will work. In later chapters I'll show you more about Strings and more specifically about Error Handling, so that you can easily capture this kind of problem and tell the user what kind of input you need.

There are currently no FAQs about Java Essential Training.

Share a link to this course
Please wait... Please wait...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.
Upgrade now


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ.

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

Upgrade now

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed Java Essential Training.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferencesfrom the dropdown menu.

Continue to classic layout Stay on new layout
Welcome to the redesigned course page.

We’ve moved some things around, and now you can



Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked