Corey Leigh Latislaw

Instead of focusing on styling in yesterday’s class, we focused on the Java code to make the calculator work. We’ve moved the styling lab and material to today’s class. If you were having trouble with the calculator portion of the class – do not dispair! Download the latest code from the classroom example so you can follow along with the styling lab today.

If you haven’t finished last week’s homework, don’t be discouraged! Join us at project night! Also, I will be posting my finished application so you can see how I implemented the project.

• Slides: Class 3 & Slides: Class 4
• Notes
• Classroom Example

Homework Exercises

Tonight will engage your artistic side and make your calculator feel like a real application.

• Create a style for operator keys. Add dimensions and colors to support the style.
• Create a drawable for the operator key states.
• Create a style for the equals key. Add dimensions and colors to support the style.
• Create a drawable for the equal key states.
• Create a style for the clear key. Add dimensions and colors to support the style.
• Create a drawable for the clear key states.

What’s Next?

We’ve only scratched the surface of the wonderful world of Android. My goal was to get you excited about this platform and wanting to learn more. Luckily, there are a lot of great resources that can help you on your way, including local meet ups.

• The Android Alliance is a monthly meet up on 4th Wednesday of every month. The next one is tomorrow, sign up here.
• Girl Develop It project night is a great place to bring things you’re working on, discuss things that have come up, and talk to teachers and peers.
• Android’s documentation is good and there lots of tutorials.
• Stackoverflow is a question and answer forum and a great resource when you run into problems implementing your app.
• If you’re looking for a book, I highly suggest Professional Android 4 Application Development by Roto Meier.

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The first half of the class will be a hands on lab focusing on last week’s homework assignment. Then we’ll discuss how to style the application.

Course Material

• Slides
• Notes
• Classroom Example

Homework Exercises

If you haven’t finished last week’s homework, don’t be discouraged! You’ll have more time to work on it tomorrow.

Tonight will engage your artistic side and make your calculator feel like a real application.

• Create a style for operator keys. Add dimensions and colors to support the style.
• Create a drawable for the operator key states.
• Create a style for the equals key. Add dimensions and colors to support the style.
• Create a drawable for the equal key states.
• Create a style for the clear key. Add dimensions and colors to support the style.
• Create a drawable for the clear key states.

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Although I love the idea of highlighting geeky leaders and businesses that make a difference in this city, I’m disappointed that the mobile community has been underserved for two years running.

Last year there was a category to recognize the best iOS app of the year. I found out about the event rather late and mounted an unsuccessful campaign to get an Android category on the roster. Although defeated, I was encouraged about the future, because the organizers promised to have a category the following year to highlight all platforms.

Fast forward to this year. I was super excited when I saw that the category list contained Mobile Developer of the Year. I ran out and bought tickets immediately for the event. Apparently submissions were low for this particular category and without warning the category was cut. I found out on the day that the nominations were announced and immediately emailed organizers to find out what had happened. They were unmoveable about giving even a short of period of time to reach out to the community to garner more nominations to reinstate the category. I spent several months debating my next move, but eventually gave up and sold my tickets for lack of enthusiasm about the event.

Last year the awards favored iOS over Android and this year both were left out in the cold. The argument has been made that it’s the community’s fault for not stepping up. However, I think the marketing message didn’t reach these communities effectively. For example, I wrote an email to the women in tech scene here to encourage them to submit nominations for various categories (a population that may have completely overlooked this award ceremony in the past). Reaching out to this community had a strong mobilizing affect – you can see this reflected in the number of women nominated for awards.

For whatever reason, I didn’t send the same email to my community – the Android Alliance. They had no idea that the event was happening or how to submit nominations. Several later expressed disappointment that they missed their chance to participate. If the organizers had mentioned that submissions were low, I would have gone out of my way to garner more. I never had an inkling that there was trouble brewing for this category.

In short, I’m very disappointed that mobile is not being highlighted at all this year. I wish organizers had reached out the mobile communities – either when selecting a category or when submissions were low. This could have been avoided if we worked together.

Full disclosure: I nominated myself for this award (as did a few others). Would I like to have been recognized, sure. But that’s not my motivation for writing this blog. My motivation is to have the Android, iOS, and Windows mobile communities recognized for its role in this city’s economy and technological innovation. I don’t want the mobile community to be overlooked a third time.

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It’s time to make our first Android application!

Course Material

• Slides
• Notes
• Code from Classroom Lab

Office Hours

If you have any questions, please feel free to reach out to the Facebook group. This forum gives you access to your fellow classmates, the TAs, and myself. In addition, I will hold Skype office hours on Thursday, August 16 from 7-8 PM to answer any questions that will help you get started. I will hold office hours again on Saturday from 4-6 PM to answer questions you may have when deeper in the coding assignment.

Homework Exercises

If you haven’t finished last night’s homework, please start there to get more familiar with the foundations of Java.

Now that we’ve laid the ground work for the calculator app, let’s make it work! Here’s what the calculator should do:

1. Consecutive numbers should be appended to the current number (Example: 1 2 3 4 5 should display 12345).
2. Create an enum that represents operation types that a calculator can perform (see below for more details).
3. When an operation is performed, store the type.
4. When an operation is performed, store the number displayed.
   • NOTE: We’re displaying as a String, but should store a number type.
   • int number = Integer.parseInt(“12345″)   // Gives the integer 12345
5. When equal is pressed, calculate the result using the operation type and stored number.
6. Division and modulus should perform integer calculations (Example: 7 / 3 = 2 and 7 % 3 = 1).
7. When equal is pressed, update the display with the result.
8. Pressing equal after a calculation is complete should show the last result (Example: 2 + 3 = 5 ==== 5, pressing equal repeatedly after the initial calculation will show as result of 5).
9. The clear button should reset the calculator state.
10. Users should be able to change their minds about what calculation to perform (Example: 2 * + / * 4 = 8, should calculate 2 * 4 because the last operation entered was multiplication).
11. Calculations can “chain” or use the last calculated number in the new equation (Example: 2 + 3 = 5 + 2 = 7).

Extra Credit (End of Class Goals)

Users don’t always do what you expect them too! Handle the following unexpected user actions or exceptional states:

• Detect division and modulus by 0. When this occurs, place the application in an error mode and display the string “NaN”. Only pressing the clear button or a number key clears this state.
• User presses equals after starting the application.
• User presses an operation before a number is entered.
• User enters a number, presses an operation, then presses enter.
• Prevent and detect integer overflow. To prevent, limit the number of digits a user can enter. When a calculation exceeds the maximum integer amount, place the calculator in an error mode and display the string “Error”. Only pressing the clear button or a number key clears this state.

Switches & Enums

Using switches and enums together can simplify the coding assignment. An enum is a handy data type that allows you to basically specify a name for an integer. Consider this example:

public enum Season { WINTER, SPRING, SUMMER, FALL }

You’d define this enum in Season.java or in your current class. Then, you create a field in your activity that stores a particular season.

Season season = Season.SUMMER;

This technique is especially useful when you want to do different things for different seasons. You could do this with normal if/else/else if blocks, but a switch statement is much cleaner:

switch (season)
{
    case SPRING:
        System.out.println("I love spring!");
        break;

    case SUMMER:
        System.out.println("I love summer!");
        break;

    case FALL:
        System.out.println("I love fall!");
        break;

    case WINTER:
        System.out.println("I love winter!");
        break;

    default:
        System.out.println("Not sure what season we're in!");
}

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