Seven Steps in Action: Testing the Algorithm

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From the course by Duke University

Java Programming: Solving Problems with Software

2166 ratings

Duke University

Java Programming: Solving Problems with Software

2166 ratings

Course 1 of 4 in the Specialization Object Oriented Programming in Java

Learn to code in Java and improve your programming and problem-solving skills. You will learn to design algorithms as well as develop and debug programs. Using custom open-source classes, you will write programs that access and transform images, websites, and other types of data. At the end of the course you will build a program that determines the popularity of different baby names in the US over time by analyzing comma separated value (CSV) files. After completing this course you will be able to: 1. Edit, compile, and run a Java program; 2. Use conditionals and loops in a Java program; 3. Use Java API documentation in writing programs. 4. Debug a Java program using the scientific method; 5. Write a Java method to solve a specific problem; 6. Develop a set of test cases as part of developing a program; 7. Create a class with multiple methods that work together to solve a problem; and 8. Use divide-and-conquer design techniques for a program that uses multiple methods.

From the lesson

Fundamental Java Syntax and Semantics

In this module, you will learn to write and run your first Java programs, including one program that prints “Hello!” in various countries’ languages and another where you will analyze the perimeters and other information of shapes. To accomplish these tasks, you will learn the basics of Java syntax and how to design stepwise solutions with programs. By the end of this module, you will be able to: (1) Download and run BlueJ, the Java programming environment for this course; (2) Access the documentation for the Java libraries specially designed for this course; (3) Edit, compile, and run a Java program; (4) Construct methods, variables, if else statements, and for each loops in Java; and (5) Use Iterables (like DirectoryResource) to run a program that iterates over multiples lines in a document or webpage or multiple files in a directory.

Solving Programming: A Seven Step Approach6:03

Seven Steps in Action: Developing an Algorithm7:51

Seven Steps in Action: Testing the Algorithm4:12

Seven Steps in Action: Translating to Code5:02

Meet the Instructors

Owen Astrachan
Professor of the Practice
Computer Science
Robert Duvall
Lecturer
Computer Science
Andrew D. Hilton
Associate Professor of the Practice
Electrical and Computer Engineering
Susan H. Rodger
Professor of the Practice
Computer Science

Hi.

We've developed an algorithm to find the perimeter of a shape.

But are we ready to turn this algorithm into code?

Well we could, but

we'd like to be confident that it's right before we do that.

After all, there were a lot we had to do to generalize our steps.

And it's entirely possible that we made a mistake.

Or perhaps we just didn't think through all the special cases.

So before we turn this into code, we should test it out.

To test the algorithm, we need a different instance of the problem,

something other than what we used to make the algorithm.

In fact, it's good if our test instance

is pretty different from the one we used to make the algorithm.

Here, we've shown a triangle

instead of the four-sided trapezoid we used when we developed the algorithm.

Before we go any further, take a second to figure out what the right answer is.

What is the perimeter of this shape?

When you finish,

you'll want to check if the answer to our simulated algorithm is correct.

And to do, that you'll need to know the right answer.

Now, we'll execute the algorithm by hand for this particular input.

As we test the algorithm, notice the similarities between the code and English.

We're going to execute this English algorithm by hand,

just as we executed code by hand.

They both work pretty much the same way.

And that's not a coincidence.

When you turn this algorithm into code,

you want to write down code that has the same semantics as the English.

The same meaning.

The code should transform the program state

in the same way that the English transforms this diagram.

So we'll start with totalPerim and set it to 0, and

prevPt being the last point in the shape.

But what is the last point?

We'll say that points in this shape start at the top and go counter-clockwise.

So this point in the lower right-hand corner is the last one.

And we'll initialized prevPt to be that point.

You will note briefly that if it is were actual Java object,

prevPt might be an error pointing at an object.

But we're going to just write down the coordinates here to keep the diagram

simple and legible.

Next, we're going to do the steps for each point.

So, we need to start at the first point,

which is this one at the top of the diagram.

And that will be the initial value of currPt as we enter the for

each repetition.

Then, we'll find the distance between these two points, which is 10.

And we'll update totalPerim to be 10, 0 plus 10.

And then, we'll update prevPt to be currPt.

Now we're at the end of our for each repetition.

So we'll update currPt to be the next point in the shape, which is (-3, -4).

When we update currPt, we go back to repeat these steps.

We repeat the steps again.

Find the distance between those two points, which is 8.

And then we update total perimeter to be 10 plus 8, or 18.

And then we update prevPt to be the current point.

Then we go back to the top of our loop, updating currPt.

We repeat these steps for the last point in our shape.

After which we've gone through all the points.

So we skip to the steps after our repetition.

Here, we can say that totalPerim is our answer.

TotalPerim is 24.

Is that the answer you came up with earlier?

Yes, that is the perimeter of this shape.

The fact that our algorithm came up with the right answer here

gives us more confidence that we generalized correctly.

We're done executing the algorithm by hand and

we have some great confidence that it's correct.

So we're ready to turn the algorithm into code.

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