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Support: For-Each Loops, part 3 of 5

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Data Structures and Performance

Калифорнийский университет в Сан-Диего

4.8 (оценок: 1,586) | Зарегистрировано учащихся: 52K

Курс 1 из 4 — Object Oriented Programming in Java Специализация

How do Java programs deal with vast quantities of data? Many of the data structures and algorithms that work with introductory toy examples break when applications process real, large data sets. Efficiency is critical, but how do we achieve it, and how do we even measure it? This is an intermediate Java course. We recommend this course to learners who have previous experience in software development or a background in computer science, and in particular, we recommend that you have taken the first course in this specialization (which also requires some previous experience with Java). In this course, you will use and analyze data structures that are used in industry-level applications, such as linked lists, trees, and hashtables. You will explain how these data structures make programs more efficient and flexible. You will apply asymptotic Big-O analysis to describe the performance of algorithms and evaluate which strategy to use for efficient data retrieval, addition of new data, deletion of elements, and/or memory usage. The program you will build throughout this course allows its user to manage, manipulate and reason about large sets of textual data. This is an intermediate Java course, and we will build on your prior knowledge. This course is designed around the same video series as in our first course in this specialization, including explanations of core content, learner videos, student and engineer testimonials, and support videos -- to better allow you to choose your own path through the course!

Просмотреть программу курса

Получаемые навыки

Trees (Data Structures), Data Structure, Linked List, Binary Tree

Рецензии

4.8 (оценок: 1,586)

5 stars
1,319 ratings
4 stars
230 ratings
3 stars
28 ratings
2 stars
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1 star
4 ratings

AE

Dec 06, 2016

Very solid review of data structures. In fact, I learned a lot of new things along the way like how to benchmark test Java code and how to properly use JUnit and other unit testing frameworks.

YK

Jan 11, 2016

I really liked this course and the way it was taught. Although I am a CS major, I really learnt a lot of other stuff from this course apart from learning the core content of Data Structures.

Из урока

Working with Strings

This week we're going to dive into the course programming project. In the first lesson you'll learn about Strings and Regular Expressions, and in the programming assignment this week you'll apply that knowledge to adding functionality to your text editor so that it can measure the "readability" of text by calculating something called the "Flesch Readability Score". This course is focused on building code that not only does interesting things, but also finishes them quickly. So, let's get started building some code!

Core: Introduction to the Flesch Readability Score5:44

Core: Basics of Strings in Java6:21

Core: Working with Strings in Java8:44

Support: For-Each Loops, part 1 of 51:50

Support: For-Each Loops, part 2 of 54:37

Support: For-Each Loops, part 3 of 54:31

Support: For-Each Loops, part 4 of 59:52

Support: For-Each Loops, part 5 of 52:01

Core: Introduction to Regular Expressions10:29

When I struggled: Regular expressions1:44

Concept Challenge: Regular Expressions9:10

Support: More with Regular Expressions8:50

Преподаватели

Christine Alvarado
Associate Teaching Professor
Mia Minnes
Assistant Teaching Professor
Leo Porter
Associate Teaching Professor

Текст видео

[SOUND]

So we saw, when we went through that method, that it actually didn't quite work for us.

And the problem that we ran into is even though we declared this pointer

to an array of characters, cArray, and the issue is that to toCharArray that method,

which was a copy of the words, arrays of characters.

It doesn't let us access that array of characters itself, and so

we ran into troubles as you saw, so let's try to modify our method a little bit and

say what if we returned a new string with cArray

as its input character array, maybe that will work for us.

Does this method now successfully return a modified word?

So we've tried again, let's focus on what we've changed.

It's this last line over here where we return something at the end of our method.

And notice that the beginning of the memory model is really the same as what we

had because right now we're just representing the input arguments,

the arguments and parameters to the method.

Now as we did before the first step of this method is to create a variable

that points to a copy of of the character array of the string,

and so we're going to have that represented in our memory model as well.

And just as before, what it's pointing to in the heap is not the character array

that we had before, but rather a copy that we create in the heap.

All right, and notice that what we're returning at the end is a new

string object and the string object is built out of this character array.

And so, maybe this will work.

So, in order to see that, let's trace through what happened.

And so after we've declared and

initialized the character array cArray, we now go into this for each loop.

And in this for each loop what we're doing is we're going through

every character in the cArray of characters.

And for each one, we're looking at the character c, so

that so means that c becomes a new variable in our memory model.

And so this is the new part for this method so I'm using a different color.

And now we have to think about what gets stored in this box, so

when we go through that first iteration of the for

each loop we've declared this character variable c, and what we store in it is

the contents of the first element of the array pointed to by the cArray.

And so the contents of this first element of the array is the character a.

Now notice this is a primitive type.

And so what that means is when we assign the variable c to have this value,

what we're storing here is a, the character a.

And notice that there's no connection between this a and

the a that's stored over here.

They're different copies of the character a.

And so in particular, when we go through this body of the for loop and

we're checking whether the contents of c agree with the content of gone.

And we say, oh this guy's an a and over here we've stored a as well and so

that means we have to reassign.

The contents of c to, instead of it's current value,

it gets the new value, whatever was stored in the variable here, so that's i.

Notice that what that assignment variable does,

is it changed the content of the box pointed to by c.

But it doesn't change the content of the character array pointed to by cArray.

And so even though we've noticed that this a actually was the same as this a,

where we've changed the character was down here and not up here.

And so even though we could go through this for loop and make all of

the modifications to c that are necessary, when we go ahead and return the value,

we're returning a new string object that's based on this character array.

And this character array has not been modified at all.

All of our modifications,

all of our assignment statements, have just changed the contents of a variable c.

And not inside this character array.

And so this method implementation still doesn't do what we're looking for.

It's not going to be our replace method.

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