Shapes: Collections of Points

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Java Programming: Solving Problems with Software

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Duke University

Java Programming: Solving Problems with Software

2344 ratings

Course 1 of 4 in the Specialization Object Oriented Programming in Java

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.

From the lesson

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.

Shapes: Collections of Points2:29

Why Semantics: Motivation to Read Code1:11

Mathematical Operators2:24

Meet the Instructors

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

Hello, we're going to learn how to calculate the perimeter of

shapes using Java.

We'll use what is called a Java Class, which you'll learn about soon,

named Shape to model polygons in geometry.

These kinds of shapes are used in many applications.

For example, a triangle is the simplest polygonal shape,

it's simply a collection of three points.

But triangles can be combined into complex shapes that are colorful or

form the basis of wireframe diagrams used in computer graphics and video games.

We'll use a Shape Java class to represent a collection of points.

We'll use a class for point and for shape to understand programming concepts

that are applicable across many programming languages.

We'll need to construct shapes by adding points one at a time.

This will allow us to create shapes like this six sided shape,

which is constructed from six points.

Here is a shape with five points.

Here is another six sided shape.

The order in which the points are added to the shape is important.

When we look at the code for the Java Shape class, we'll also need methods for

accessing the points, either one at a time or using other approaches.

We'll likely want to create operations or

methods that use shapes, like drawing a shape or finding the perimeter of a shape.

We've seen that shapes can have many points.

Our shape class is simple, but

we could expand it to create complex shapes of many, many points.

Like this butterfly.

When viewed more closely, it's clear that the butterfly is

simply a collection of colored triangles, like the wireframe drawing we saw earlier.

The shape class we'll look at is very simple.

Circles aren't really a finite collection of points.

So circles and some other shapes are harder to model using our Java class.

In geometry, a circle is an infinite collection of points

that are all the same distance from the center of a circle.

Our Java class is just a finite collection of points.

However, even with our simple class, we could model a circle using many points,

as shown in the diagram here.

So, even our simple class will prove very powerful.

After we cover some of the basics of writing programs in Java,

we'll explore the point and shape classes in more detail.

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