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Do curso por Duke University

Java Programming: Solving Problems with Software

2281 classificações

Duke University

Java Programming: Solving Problems with Software

2281 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

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.

For Each Loops7:27

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

Now that you have the high level concepts,

let us delve into the step by step execution of our example Point code.

We're going to start in main which we'll talk about more later.

Args gives you access to

the command line arguments which you won't need for quite a while.

So we're just going to ignore that.

The first line declares point P1 and initializes it to a new point.

Note that classes are types,

so we can use class types that we make to declare variables.

Here we want P1 to be a point.

Until we finish evaluating the right hand side,

we're going to draw this as an arrow with a flat end.

We'll use this notation to indicate when a variable does not reference an object.

Note that this is a bit different from numeric variables

like ints whose initial value is zero.

We've colored this flat ended arrow red to

remember that we have not yet explicitly initialized this variable.

Now, let us evaluate the right hand side of the initialization expression.

We're doing new which will create a new object.

What type of object are we going to create?

We'll look right after new and see that we are creating a new point.

So we're going to draw a box for a point which has fields x and y.

Note that the box we just drew is not in the frame but is outside of it.

It is in a different area called the heap.

Anytime you use new,

you create data in the heap.

The important difference is that data in the heap does

not go away when a function returns destroying its frame.

Note that we have put zero in the field of this new point and

colored them red as we have not explicitly initialized them yet.

Speaking of initialization, remember that we said that the whole point

of a constructor is to initialize a newly created object.

The next thing that happens is that we call the constructor to initialize this point.

As with any call,

we set up a frame and pass parameters.

However, constructors and methods take

an additional implicit parameter which tells them which object they are operating on.

That parameter is called this and its value

is an arrow which points to the object that is being acted on.

In this case, this points to the object that we are

creating to tell the constructor which object to initialize.

Now, we enter the code for the constructor and begin executing statements there.

The first line says X gets start X.

There's no X in this frame,

so where do we store the value of start X?

Here X refers to the field inside of this object.

That is, we want to put start x's value

into the X field of the object we're initializing.

So to find the right box we follow the arrow for this and then

look for the X field in this object and store the value three into that box.

On the next line,

y again refers to the field inside of this object.

So we update that field to be four.

Now we have finished the code inside

the constructor and are ready to return to main at call site one.

Back in main, we need to finish this assignment statement.

To do that, we need to store the value of the right hand side into the box for P1.

A new expression evaluates to an arrow pointing at the object that it created.

So we'll make P1 to point at the newly made point.

The next line does a similar thing.

It declares P2 and initializes it to a new point.

So once again we create a box for P2.

We haven't initialized it explicitly yet.

So we have a default value of

a flattened arrow meaning it does not point to any object yet.

We color red to remember that it has a default value.

We then create a new point with its x and y fields set to default values of zero.

And we call the constructor to initialize this point.

Notice how this points at the newly created point.

With multiple points in our world,

it is important that we can keep track of which point we are working on.

We then initialize the x inside of this point to be six as before we found

the right box by following the arrow from this

and we initialize the y inside of this point to be eight.

Now we have finished the constructor and are again ready to return to main.

In main, we finish the assignment statement

setting P2 to point at the newly created object.

We'll stop there and pick up with executing the method call in the next video.

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