While Loop Syntax and Semantics

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來自 Duke University 的課程

Java 程序设计：使用软件解题

2561 個評分

Duke University

Java 程序设计：使用软件解题

2561 個評分

課程 1（共 4 門，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.

從本節課中

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

與講師見面

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

To implement our improved gene-finding algorithm,

you need to learn about while loops, the code that generally comes up when you have

a step in your algorithm like, as long as some condition is true.

You can see an example of a while loop here.

Let's look at this example to delve into the syntax and

semantics of the while loop.

All while loops start out with the keyword while.

Then, they have some condition, sometimes called a guard, in parentheses.

This is the condition that you want to check to see if you should continue

doing the loop.

Then you have the loop body in curly braces.

These are the statements that should be executed each iteration of the loop.

Let's walk through this example to understand the semantics of the loop.

What it means?

For example, let us assume that x was previously declared and

initialized to zero.

And y was initialized to 7.

When execution reaches the while loop,

the first thing that happens is Java evaluates the condition, is x less than y.

In this particular case, that means is 0, less than 7?

0 is less than 7, so the condition evaluates to true.

Since the condition is true, execution will enter the loop body and

continue executing statements there.

The first statement prints x which is 0.

So, we would output the line 0.

The second statement sets x to x + 3 which would update the value of x to be 3.

Now, execution has reached the end of the loop body.

The close calibrates marks its end.

Then execution goes back up to the start of the loop, and

we are right back where we started, but the variables have different values.

X is 3 instead of 0.

We continue following the same rules.

Evaluate the condition, 3 is less than 7.

The condition is true so we enter the loop body.

Print x which is 3, and update x to be 6.

Now we've reach the end of the loop again so we go back up to the start of it.

And again follow the same rules, check the condition, it is true so

we enter the loop body print x which is 6.

Update x to be 9, and now we have reached the end of the loop body again, so

we go back to the start.

Yet again we follow the same rules.

Now when we evaluate the condition, something different happens.

Is 9 less than 7?

No, so, the condition is false.

Instead of entering the loop body, we go past it.

We would then continue executing whatever statements come after the loop.

Great, now you've learned the basics of while loops, their syntax,

the grammatical rules for writing them, and their semantics, their meaning.

Now you're ready to go code your improved gene finding algorithm.

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