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Core: Adding markers

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面向对象 Java 程序设计

加州大学圣地亚哥分校

4.7（3,506 個評分） | 160K 名學生已註冊

課程 2（共 4 門，面向对象 Java 程序设计專項課程）

你是否曾想过大型软件项目诸如Google搜索引擎是如何开发的？本课程将帮助你超越平凡编程，去学习设计和开发更加复杂的Java软件项目（尽管还没到Google搜索引擎那种级别！）我们会探索如何将一个大的项目分解为层次结构的类，以及如何通过现有的库来增强项目的功能。我们也会探究一些搜索和排序的核心算法。在学习过程中，你将要开发一个令人兴奋的有着图形用户界面（GUI）的交互式应用程序。我们期待本课能启发你去创造。你即将进入课程项目，每节课所涉及的原理概念都设计成可直接应用于项目功能拓展。视频课程同时包括核心课程内容和现实中的软件工程师的来信和故事，与正在学习本课的真实学生之间的对话，以及一些你遇到困惑时可去观看的补充视频。（本课程若发现字幕错误请发送邮件到caesarguangli@hotmail.com，谢谢！）

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Logic Programming, Java Programming, Object-Oriented Programming (OOP), Sorting Algorithm

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4.7（3,506 個評分）

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KP

Feb 21, 2016

Enroll this course if you intend to become a programmer and need fundamental knowledge in Object Oriented Programming. Here you can study the subject and apply new things in a real curious project.

OE

Aug 06, 2017

This course made me understand java concepts in an easy way, and made me realize certain internal workings in Java I haven't seen elsewhere. I love their method/process of tutoring. Awesome job!

從本節課中

Graphical output: Creating GUIs and Displaying Data

Now that you have the tools to write and trace object oriented code, let’s get back to developing the project! In this first (real) part of the project, you will create an interactive graphical map that will display geospatial data. This is a highly interactive week, so make sure you’ve got Eclipse loaded up! We encourage you to play around as you watch the videos. Some of the code that we use in the videos is in the demos package in the starter code you set up for this course. Open it up and experiment with it while you're watching the videos. We also encourage you to dive right into the programming project, even before watching the videos, if you want. The programming assignment instructions are in the last lesson of this week - you can watch a video walkthrough of the instructions and also read the step-by-step directions in the accompanying reading. There’s lots of room for creativity, too, so have fun!

Core: Why Processing?1:08

Support: Using Documentation7:08

In the Real World: Documentation3:24

Core: Setting up map visualization9:49

Core: Adding markers5:27

Core: Using live data11:18

Bonus: Visualizing life expectancy0:29

Bonus: Setting up the map4:48

Bonus: Representing data8:53

Bonus: Coloring markers11:42

Support: ArrayLists and Generics8:54

教學方

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

腳本

[MUSIC]

So we're going to continue building our map application displaying earthquakes,

and we're ready to start adding content to the map that we set up before.

So then the question is how do we add that content?

And we know that our map is, well, it's part of a class that extends p applet.

And so, the two main methods that we've got

where we're doing a lot of the hard work are the set up method and the draw method.

And so, it's a question where do we put the definitions

of all of these new objects that we want to create that will let us

point ad various parts in the map and remember that the setup method gets

executed exactly once at the beginning of when the p upload is launched.

Whereas the draw method that gets executed over and

over again, every time we want to refresh the view.

And all of these objects that were creating the pointers

to various milestones and features of the map

we don't want to create a new object every time the screen gets refreshed,

what we love to do is just have a single instance of those class

that represents a particular point that we're thinking about.

And have that point somehow associated with the map as a whole.

And then every time we need to refresh the map we just say

hey refresh every thing that we've already created.

And so for that reason all of these definitions.

All of the work that we're about to do will get put in the set up method and

then when we execute the map.draw method.

It within the p draw method, that mapped our draw method,

will go through all the objects that are associated with or

attached to a map object and will refresh them as well.

So, let's think about, adding a specific marker,

to denote a particularly significant earthquake that happened in Chile in 1960.

And so, what we'd like to do perhaps, is indicate that location as something

o note, and then put a dot on that location in our graphical representation.

So let's think about some code that we could use to do that.

In the first line of code, notice that we're working with coordinates, which

should be a little bit familiar to you from what Christine was doing earlier so

one of the great things about working with a library of methods and

data types that were special built for

a particular purpose is that a lot of the data types that we would naturally need

have the defined focal ready and location is one of those examples.

So in our earlier videos we actually defined a class called simple location and

we tried to built in some of the functionalities that location

ought to have but we see over here in the documentation for

unfolding maps that we already have that in the location class.

And so notice that there are a couple different constructors depending on which

parameters we want to use and then some public methods that we can use

to both access and modify some of the properties of the location objects.

So the first thing that we would want to do when putting a marker on this

significant earthquake on its location in the world is to create

a location object and set its coordinates to be the coordinates of the epicenter.

Now once we have that location object that still isn't associated with the map, and

the way that we can associate or

highlight a particular location on the map Is to create a marker.

So, a marker is, well, it's what you think it might mean, and

this is the beauty of having our Java objects mirror the, it'd be really

models for the real life objects, so that our code is readable and intuitive.

So a simple point marker represents a single location, and

it represents it using a circle.

Now, notice that there's something else in this documentation.

Notice the documentation points out that the simple point marker implements

something called a Marker, and it's an interface called a Marker.

Now, an interface is

something that indicates that we're dealing with an abstract data type.

It's like a promise between the programmer and

the person using the library's code that any data type

that implements the abstract data type marker will have certain behaviors,

will allow certain functionalities and

what the interface let's us do is hide some of the details of the implementation

of how those functionalities are actually put into practice.

So in our particular application, we don't really care

whether our marker is a SimplePointMarker or some other kind of marker.

All we care about is that it's a way of denoting a specific location on the map.

And so in our code what we might say is that the variable val

of type marker gets assigned to the object of type SimplePointMarker.

So when we're creating an object we have to give it a concrete data type.

So that it can actually,

you can actually use a specific details of the implementation of that class.

But when we're going to be using or pointing to that object,

all we'll need to know about it is that it's some kind of marker.

And in particular, what we'll be doing with it is adding that market to our map

so that it gets displayed, and so

that then when we execute the draw method, that marker will show up on our map.

And so, what we see is the map that displays the location of the Chile

earthquake and coming up, we'll add richer data and more date.

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