Introducing Java

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Introducing Java

• CSC1401

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Course Goals

• Teaching programming concepts
• In a real language

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Course Approach

• Alternate between Alice and Java as we learn
  programming concepts
• Some concepts well explore first in Alice
• Others well explore first in Java
• The problem of Java
• Its hard
• Well use specially created graphics libraries to
  help us

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Java libraries

• What is a Java library?
• Its just a class or several classes
• In Alice, classes were located
• Local Gallery
• CD Gallery
• Web Gallery
• In Java, well need to tell the computer where to
  find the classes
• Setting the classpath (this is the directory
  where the classes will be located)
• Or, using an import statement in our Java program
• Well see how to do this in lab on Friday

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Important object-oriented concepts

• Class
• Object
• Method
• Parameter
• Sequencing (Do in order vs. Do together)
• Design

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Alice Java similarities

• We are going to find that Alice and Java are
  quite similar, and that concepts learned in one
  language immediately apply to the other
• There are some differences, mostly mechanical,
  between the 2 languages

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Some differences between Java and Alice

• Alice uses a drag and drop editor

• Java has Integrated Development Environments
  (IDEs) that generally require typing code. Well
  be using one called JGrasp

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Alice-Java Differences

• Classes are found in the local gallery, the CD
  gallery, or the web gallery

• Classes can be located anywhere, but you need to
  tell the computer where they are

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Alice-Java Differences

• The main program is generally world.my first
  method

• The main program is generally public static void
  main (String args)

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Alice-Java Differences

• In Alice, objects are added to a world by
  dragging them and dropping them into position

• In Java, we use the new keyword. We also use the
  constructor to specify such things as where to
  place them.

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Alice-Java Differences

• In Alice each method is located on a separate
  window but you can export all of the dragons
  methods into a single html file

• In Java, all of the methods for a single class
  are in one window

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Alice Java Differences

• File names always end in .a2w (and sometimes .a2c)

• File names always end in .java

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Alice-Java Differences

• To run an Alice program, just click on the play
  button

• Running a Java program is a 2-step process
• Click on compile. This will make sure you dont
  have any typos and generates a .class file
• Click on Run

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Alice-Java differences

• In Alice, an objects methods are located in the
  object pane at the lower left of the screen

• In Java, we need to look at an html file (called
  Javadoc- short for Java documentation) to see an
  objects methods

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Alice Java differences

• In Alice most objects (except for billboards) are
  3D

• In Java, most of our objects will be 2D. Java
  supports 3D, but its much harder to program.

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Java Example Turtles

• We will work with Turtles in a World in Java
• We do this by writing a Turtle class definition
• Turtle.java
• We compile it to convert it into something the
  computer can understand
• Bytes codes for a virtual machine
• Turtle.class

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History of Turtles

• Seymour Papert at MIT in the 60s
• By teaching the computer to do something the kids
  are thinking about thinking
• Develop problem solving skills
• Learn by constructing and debugging something
• Learn by making mistakes and fixing them

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JGrasp Demo

• Opening a new Java file

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Using Turtles

• Add bookClasses to your classpath to use these
  classes

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Telling JGrasp where to find the Turtle class
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Classpath part 2
?
Then click on OK Then click on Apply Then click OK
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Turtle Demo

• Writing a Turtle program
• class
• public static void main(String args)
• versus
• // and /
• new
• Compiling and running and stopping
• Looking at the Javadoc

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Assignment

• Read Media Computation Chapter 3, Sections 1
  through 5
• Classes
• Objects
• Methods