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Do curso por Duke University

Java Programming: Solving Problems with Software

2096 classificações

Duke University

Java Programming: Solving Problems with Software

2096 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

All right, so you've been learning about while loops and break statements and

working on your gene finding algorithm.

And your current task is to write a method which will print out all the genes in

a sequence of DNA.

So we have here the print all genes method which takes in a string for the DNA and

has the algorithm or pseudo code that we came up with in a previous video.

Now we have earlier here in this code the gene finding algorithm

that you developed along with Owen in a previous video.

And we're just going to make one small change to it.

I'm going to have it take one more parameter to say where to start and

this is going to let us start looking for

a gene somewhere in the middle of the sequence of DNA.

So once we've found one at the beginning we can start looking for

one after that, by passing this index, and we'll just pass that to

index of the teller where to start looking for the first start code on.

So with that small change, we're going to go back here and

start translating our algorithm into code.

The first thing we said to do was to set the startIndex to 0.

So we haven't made a variable called start index yet, so the first thing we need to

do is declare startIndex, it's going to be an int since we're setting it to 0.

It's going to tell us the position of the string,

also a good clue that it's an integer.

And then we're going to repeat the following steps.

So you're used to repeating steps by now.

You've done things for each pixel or each of a variety of other things.

For each as a lot, you've also seen some examples of while,

where you've had a condition for as long as something.

But here we want to repeat some steps,

and then figure out somewhere else inside those steps when we're done, so

we're going to write while true, and then put curly braces around our steps.

And then we're going to go in here and we're going to start doing stuff, and

then figure out when we want to stop repeating these.

Now we want to find the next gene after startIndex.

Finding a gene is a big complicated step.

You've been devoting lots of effort and thought into how to do that.

Fortunately we've abstracted that out into a method, so we can just call it.

And let findGene that we've already written do all of that work for us.

So what does findGene take?

It takes a string for the dna and int saying where to start, and

then it returns a string.

So here we want to call findGene passing in what dna?

Well, this dna that we're working with.

And where do we want to start?

At startIndex.

And then it's going to give us back a string as its answer, so

we want to give that a name.

I'm going to call it currentGene.

We didn't say to give it a name in our steps, but

we kept referring to it without a name.

We kind of know what we mean, but

it's good to give things names in your steps anyways.

And now we can refer to that gene that we found.

If no gene was found, leave this loop.

So if something is the case, do some other steps.

By now, you should be getting very familiar with if statements.

So if no gene was found, how do we know if no gene was found?

What does findGene do if there's nothing left?

If you don't remember, we can go back up here and look.

You can see that it returns this empty string.

So we want to know, is currentGene the empty string?

Fortunately for us, strings have a .isEmpty method,

which will tell us if they're the empty string.

How would you do that if you didn't know?

Well, you could go look at the Java documentation.

Are there other ways to figure out if a string is empty?

Sure, you could see if its length was zero for example.

Any way that you can find that works is a good way to do it.

All right, so if this Gene is empty, if current Gene is empty and

we didn't find it, what do we want to do?

We want to leave this loop, that is, we want Java's executing along and

it gets here.

We wanted to jump down here pass this loop,

that's exactly what a break statement does, which you just learned about.

So we would get here and then come down here,

we basically put the loop condition in the middle.

All right, if we don't break out to that loop, we want to print out that gene,

System.out.println, hopefully you're getting somewhat familiar with that.

We can print out that currentGene and

then we want to update statIndex to be just past the end of the Gene.

All right, so now this seems a little tricky.

We wrote a step that's a little bit complicated.

Maybe we have to think it through a little bit.

Let's just go down here to where I've got some testing and

think about what we are going to do.

I've written some methods to help us test, and

let's think through one of these cases here.

So this testOn just prints out that we're testing it and then it does printAllGenes.

So, we say okay, start index is going to be zero.

We're going to find this gene right here, which is length nine, right?

And so then after that we would want our new start index to be nine, okay?

So we might think we just want to add the length of the gene

that got us from 0 to 9.

That's a good first guess.

Now lets think about this next one.

So then, we're going to go, and we're going to find this next gene here,

which is length 3, 6, 9, 12, 15.

But that didn't start right where we left off, right?

So if we were to only add 15, we'd end up here in the middle of this gene,

and we want to end up over here.

So what do we need to do?

Well, we need to add the length to the start position of this gene.

How can we find that gene?

Well, index() is becoming your friend, right?

So startIndex is going to be dna.indexOf(CurrentGene,

startIndex) + currentGene.length.

That seems kind of magical, let me just explain that again really quickly.

All right, we want to find where that current gene was in the string,

we can do that by looking for it again starting at start index.

So that's going to tell me, this gene was right here.

And then we can add its length to end up past here.

That'll work for this first one because looking for

this first gene from the start index of zero is just going to give me zero.

And when I add its length, I'm going to end up here, all right?

So that still doesn't make sense to work it out on your own.

So, I'm now going to hit Compile.

All is well there and now I'm going to come over here and

I'm going to make a new object and then I'm going to run my test method.

And, you can see it says, all right, I'm testing print all genes on this

sequence of DNA, and it's got two of these.

Back over in my code, I tried to make this a little easier for us to see.

So we've got this gene here, and then we've got this gene here, and

these little vs are just for me to keep track of the codons.

And those were what it printed here.

I tested it on the empty string,

I wouldn't expect it to find any genes in there.

But it's always good to test on these wacky corner cases where maybe our code

would break if we weren't careful.

We didn't find any genes, but our code didn't crash either, that's really good.

And then on this one, where I have this one long gene here, which we found and

printed out.

And then this really short gene here which we also found and printed out.

So that worked well and the important thing here, the new lesson was this while

true, figure out if we want to keep going in the middle and then break.

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