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Do curso por Duke University

Java Programming: Solving Problems with Software

2508 classificações

Duke University

Java Programming: Solving Problems with Software

2508 classificações

Curso 1 de 4 em Specialization Object Oriented Programming in Java

Building upon Duke’s “Programming and the Web for Beginners” course, you will grow in your ability to be a problem-solver and programmer by writing Java programs. We are excited that you've chosen to learn Java with us! You will soon be able to solve problems that you find interesting and useful by practicing a design process you will learn in this course. Java concepts presented in this course include basic control flow; object-oriented concepts including classes and methods; custom, open-source classes; and a design-implement-debug process that you can continue to leverage as you build your experience and knowledge of programming principles. The custom, open-source classes will provide a consistent application programming interface (API) so that you can write programs that access and transform images, websites, comma separated value (CSV) files and other data files using simple and accessible coding idioms built on the Java Iterable interface. You will learn to design, test, and debug programs and to find and read Java documentation that can serve as the basis for continued study of Java and programming. After completing this course you will be able to: 1. Edit, compile, and run a Java program; 2. Use conditionals and for loops appropriately in a Java program; 3. Use Java API documentation in writing programs. 4. Debug a Java program using the scientific method; 5. Develop 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 more than one method.

Na lição

Strings in Java

This module begins with a short presentation from Raluca Gordân, an assistant professor in Duke University’s Center for Genomic and Computational Biology, about an important problem genomics scientists encounter regularly: how to identify genes in a strand of DNA. To tackle this problem, you will need to understand strings: series of characters such as letters, digits, punctuation, etc. After learning about Java methods that work with strings, you will be able to find genes within a DNA string as well as tackle other string related problems, such as finding all of the links in a web page. By the end of this module, you will be able to: (1) Use important methods for the Java String class; (2) Use conditionals, for loops, and while loops appropriately in a Java program; (3) Find patterns in the data represented by strings to help develop the algorithm for your program; (4) Understand the importance of designing programs that keep different data processing steps separate; (5) Use the StorageResource iterable for this course to store some data for further processing; and (6) Rely on Java documentation to better understand how to use different Java packages and classes.

Introduction0:48

Conceptual Understanding4:01

While Loops9:30

While Loop Syntax and Semantics3:06

Coding While Loops6:45

Three Stop Codons5:03

Coding Three Stop Codons - Part I7:45

Coding Three Stop Codons - Part II4:35

Logical And / Or8:01

Coding And / Or6:52

Finding Multiple Genes5:16

Translating to Code8:00

Conheça os instrutores

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, welcome back to gene-finding, yet another time.

In this version of the program that we're writing to find genes, we're going to

make one small change to what we return when we look for a stop codon.

And that change is going to mean that we have to use some

complex boolean expressions using ands and ors to make our code work properly.

So as we've already seen, the one small change we're going to make

is that instead of returning dnaStr.length() to indicate that

no stop codon was found, we're going to return -1.

That's a good value to return to indicate that nothing was found, because now

our code mirrors what for example the indexOf method in the String class uses.

It uses -1 to indicate that no string was found when searching.

Now our findStopCodon method also returns -1.

Now that change means that our test function won't work correctly.

Remember, we had a test function down here.

These functions will now fail because they didn't find that.

So to see that, very quickly, I'm going to run this new class,

create an object on the object workbench, and test the findStopCodons.

And you can see I got an error 26 twice.

And that's because in my program, I had if it's not equal to 26.

So if I change that to -1.

Compile.

And now test my program again.

Finding stopCodons.

I can see that my tests finished.

So my test program needed to change to

recognize this return value of -1 rather than the length of the string.

Now I'm confident that my stopCodon method, with this one small change,

works correctly and that it returns -1 to indicate that no stopCodon was found.

That means my findGene method is also going to need to change.

Rather than using Math.min, I'm going to need these boolean expressions that you've

just learned about.

And I've put here in my comments what those

boolean expressions are supposed to do.

So I'm going to simply translate this stuff,

the comments from my seven step process, into code.

And what that code says here is,

if (taaIndex == -1 || and

we use that double vertical bar for

or, or (tgaIndex != -1

&& tgaIndex < taaIndex).

Now, that's a lot.

So let's look and make sure we got that right.

It says, if taaIndex equals -1 or

tgaIndex is not equal to -1 and

tgaIndex is less than taaIndex.

In that case, it says, set minIndex to tgaIndex.

So I'm going to say minIndex = tgaIndex; just as it says there.

That means I'm going to not use these versions of minIndex,

which werer from before.

But if I compile this code,

I'm going to get an error message, something about temp.

So if I comment that out.

Let me comment all of these out.

Now I get that variable minIndex isn't known.

So I'm going to define minIndex.

And I need to give it a value.

I need to give it some value.

I'll just give it 0.

I'm going to put in my else statement here.

What it says to else set minIndex to taaIndex,

else minIndex gets taaIndex.

So what I've got now in my code

is a translation of if taaIndex is equal to -1 or

tgaIndex is not equal to -1 and this expression,

then set minIndex to tgaIndex, also set minIndex to this value.

Then, I still have yet another boolean expression to write.

I need to write, if minIndex is equal to -1 or

tgaIndex is not equal to -1 and

tagIndex is less than minIndex.

In that case, my comments say, set minIndex to tagIndex.

So I'm writing that.

I'm simply translating this into my code here.

Finally, it says, if minIndex is equal to -1 rather than dna.length(),

return the empty string.

Otherwise, return this.

My program compiles, well, almost compiles,

I forgot second a parenthesis up here, but that's an easy thing to fix.

Well, maybe not fixing it that way by erasing it all.

Maybe I should type in a parenthesis instead.

Now when I compile my program, it works.

How do I test this?

Before, in the previous version, I didn't have a test program, a test method.

Now I do.

I have my test method, findGene.

So I'm going to try that out.

See if it works.

Right-click to create an object.

Right-click to testing findGene().

And it just simply printed, tests finished.

Which is what I wanted, since in findGene() I looked for a gene.

I found this start codon, and I found this stop codon, TAA.

Now, I could change this TAA to a different stop codon, and

I would keep testing those to make sure that my method works correctly.

I'll leave that to you, because as we've already seen,

testing is as important as writing your code.

Because you need to be sure your methods work correctly.

Have fun testing.

Have real fun programming.

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