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Functions

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Java 程序设计：使用软件解题

4.6（2,796 个评分） | 120K 名学生已注册

课程 1（共 4 门，面向对象 Java 程序设计专项课程）

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.

查看授课大纲

您将学习的技能

Algorithms, Problem Solving, String (Computer Science), Java Programming

审阅

4.6（2,796 个评分）

5 stars
2,040 ratings
4 stars
548 ratings
3 stars
114 ratings
2 stars
33 ratings
1 star
61 ratings

DN

Aug 08, 2016

You need a little more experience in coding that just the first course, or try not to leave everything by the end of the week(as I did) to find what you need for the assignments. Great course !

JS

May 19, 2019

Really practical course content with great tutorials. The programming assignments are fun and challenging and deal with real world data and problems which makes the course all the more useful!

从本节课中

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.

Conditionals3:25

教学方

Owen Astrachan
Professor of the Practice
Robert Duvall
Lecturer
Andrew D. Hilton
Associate Professor of the Practice
Susan H. Rodger
Professor of the Practice

脚本

The next important idea to understand is function calls.

Functions extract a computation out, giving it a name and parameters.

You then can use the function to perform that computation without rewriting it.

You can also think about what the function does and not how it does it.

Technically speaking, Java doesn't have functions.

It has methods since all code in Java is inside of objects.

However, before we learn the more complex behavior of objects and methods,

we'll learn the basic principles of function calls.

These concepts will then lay the foundation for understanding method calls.

We have three functions here.

My function, f and g.

Why are we starting at g?

We'll assume for now that you chose to call g from the BlueJ interface.

Later, you'll learn about the main method which is where programs start when you run

them outside of BlueJ.

We start with a frame for g and

with the execution right at the start of that function.

The first line declares a, so we create it's box inside of the frame for g.

Next, we're going to set a equal to the value of the function call

myFunction(3, 7).

To evaluate this expression,

we need to create a frame of the function that we're calling.

In this case, myFunction.

This will hold the parameters and variables of myFunction.

Next, we pass the parameters to myFunction.

We create a box for

each parameter with the names coming from the function declaration, x and y.

We initialize these by copying in the values of the expressions that were

passed.

Here, 3 and 7.

Next, we need to note where to return when we finish executing my function.

This location in the code is named the call site.

The place where the function was called.

We'll note it with a marker one in the code and

put the same marker in the corner of the frame.

Finally, we move the execution arrow into myFunction and start executing code there.

Here, we declared an initial of z.

Evaluating the expression 2 times x minus y.

The values for x and y come from the frame from myFunctions, 3 and 7 respectively.

So, z will be -1.

Now, we have reached a return statement.

Return statements tell us to leave the correct function,

returning to the call site noted in the frame.

They also tell us the value to return to the caller.

The first thing we need to do is evaluate this expression

to obtain the return value.

Here, the expression is z times x.

So we evaluate -1x3 and we get -3.

Next, find where we should return.

This is the call site we noted in the frame,

then we copy the return value back to the call site.

The function call evaluates to this return value.

We move the execution arrow back to the call site and destroy the frame for

the function we just returned from.

Now, we're back in g.

The call to my function evaluated to -3.

So, this line behaves like a gets -3.

We'll finish that assignment, putting -3 in its box.

Our next line again has a variable declaration and a function call.

We make a box for b and go through the same process to call f.

You make a frame for f and past parameters.

This time, there's one parameter n, whose value is a times a which is 9.

We know where to return and begin executing code inside of f.

Our next statement is a return statement, but

the expression involves a function call.

So, we have to evaluate that call before anything else.

We start with a frame and pass parameters.

X gets a value of n, which is 9.

And y gets a value of n+1, which is 10.

We know the call site will use two this time since we are already using one

somewhere else and move the executioner to the start of myFunction, and

start executing code there.

We declare z and initialize it to a.

Now, we are ready to return from my function.

We evaluate z times x which is 72,

then we find the call site noted in the frame and copy the return value 3.

Finally, we move our execution arrow back to the call site.

Destroying the frame from myFunction.

Now, we pick up where we left off in f using 72 for

the value of the call to myFunction.

We evaluate 3 plus 72 to get 75.

Since we're evaluating the return statement, this is the return value of f.

So we find the call site and copy the return value there,

then we return to that call site.

Destroying the frame for f.

Now, we can finish the initialization of b.

B gets 75.

Lastly, we reach the return statement for g which is where we started.

When we return from the function where we started, we are done.

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