[PPT] - Introduction to Java Programming Design goals Language features PowerPoint Presentation

SLIDE 1

Introduction to Java Programming

Design goals Language features Running sample code Tools support A1

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SLIDE 2

Origin

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Java was developed by Sun in the 1990s, as an alternative to C++.
Designed to be multi-platform
Compiles to bytecode (IR) that runs on a Java Virtual Machine.
Binary compatibility across platforms (i.e. you can deploy the compiled

code to multiple targets and it will run).

Object-oriented language.
Strongly-typed, static compilation (to bytecode).
Strong library support for different application styles and paradigms.
Open source under GNU GPL in 2007
Sun and Java acquired by Oracle in 2010
Why?
Supports Win/Mac/Linux desktop + Android

SLIDE 3

Java Tools Installation

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Java JDK https://adoptopenjdk.net IntelliJ Community https://www.jetbrains.com/idea/download You will need to install the Java SDK 11 and IntelliJ 2019.3 Community.

SLIDE 4

Java Documentation

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https://docs.oracle.com/en/java/javase

SLIDE 5

Virtualization

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Java source files (.java extension)
compile to bytecode (.class files)
Java Virtual Machine (JVM) runs it
Supports Just-in-Time (JIT)

compilation for near-native performance.

JVM can execute code from any

language that compiles to JVM bytecode (e.g. Java, Scala, Kotlin)

Java runs everywhere by having a

JVM for each target platform (Mac, Linux, Windows, Raspberry Pi, Arduino, car OS, toasters…)

http://viralpatel.net/blogs/java-virtual- machine-an-inside-story/

SLIDE 6

Compiling Java Applications

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Compile java source files using `javac’

You will often have multiple class files (typically one per .java file)
You can compile all at once e.g. `javac *.java’

To run an application

Use the `java' command with the name of the class file containing the

`main()’ method:

// compile // execute

Java files contain classes.

Each file must contain a class with the same name as the file.
One class should typically have a main() method

SLIDE 7

Using Libraries

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Classes are grouped into ”packages” (collection of classes)

package keyword to assign source to a package
a package is a subdirectory
It’s also the name of the namespace for a class file

The package for these Java source files will be net.codebot e.g. net.codebot.Main Use `import` at the top of a source file to import a class from a different package.

There are 3 classes here: Main, SomeClass1, SomeClass2

SLIDE 8

Java vs. C++?

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Java “feels” like C++ in some ways…
C++ syntax w/ semi-colons
Classes and “standard” OO features
Static typing: compiler checks your program when its compiled
But Java isn’t C++
No headers! Single file declaration and definition.
No pointers! Reference or value types, but no raw addresses.
No operator overloading. Use methods like equals() or plus()
No support for multiple inheritance. Use interfaces instead.
Garbage collection! No need (or support) for destructors.

SLIDE 9

Hello World!

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class definition static main constructor

Things that stand out

Top-level class definition (remember that Filename matches Class name)
Static main method is scoped within the class
No-argument constructor

Compiling and running it > javac Hello.java > java Hello

compiles to Hello.class executes Hello.class

Hello.java

SLIDE 10

Command-Line Parameters

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Command-line arguments are passed to the main() method as an

array of Strings.

The shell will automatically expand wildcards, so that each filename

comes in as a string.

See public/code/04.java/CommandLine

SLIDE 11

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constructor methods main fields class

Bicycle.java

SLIDE 12

Useful Packages and Packages

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Package Classes (Examples) Description java.awt Color, Graphics, Font, Graphics2D, event. Base classes for creating user interfaces and for painting graphics and images. javax.swing JFrame, JButton, JList, JToolbar ”Lightweight" components that works the same on all platforms. javafx.* Scene, Stage, Button, ”Lightweight” components that work across all platforms. More “modern” than Swing. java.io File, FileReader, FileWriter, InputStream Provides for system input and output through data streams, serialization and the file system. java.lang Boolean, Integer, String, System, Thread, Math Provides classes that are fundamental to the design of the Java programming language. java.util ArrayList, HashMap, Observable Contains the collections framework, legacy collection classes, event model,…

SLIDE 13

No Pointers!

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Parameters are passed by value. However, this isn’t always obvious.

Primitive types (int, float, etc.) are allocated on the stack and

always passed by value.

Objects are allocated on the heap, and the address is passed-by-

value

Java uses pass-by-reference semantics, so it appears as-if you’re

passing by reference.

Practically, you can treat Java as passing objects by reference.
There are no pointer semantics in Java
i.e. no *, no &, no out, no ref

both refer to same memory

n the heap

SLIDE 14

Inheritance

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Inherit some methods or fields from a base class (“is a”)
Very common in Java to extend and override other classes
Example:
“Mountain Bike” is-a “Bike”
Mountain bike inherits speed and gear fields
Mountain bike defines addition field for suspension type

Bike Mountain Bike

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inner derived class ” Meow! “ “ Woof! “ abstract inner base class top-level class

Animals1.java

SLIDE 16

No Multiple-Inheritance

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Java only supports single (class) inheritance
However, to specify complex class behavior, you can use interfaces
An interface represents an API (i.e. it defines functionality)
It represents a set of methods a class must have
You can’t instantiate an interface
Essentially, it’s a pure abstract class
Classes can choose to implement an interface
A class that implements an interface must implement *all* of the

methods in the interface

A class can implement multiple interfaces, representing different

behaviours that the class wants to support (e.g. you might have interfaces indicating that something printable and loggable).

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The interface Pet is like a type interface implementations

Animals2.java

SLIDE 18

Managing Errors

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You can use things like error codes and check return values in your
wn code, but system libraries and classes use exception handling.
You need to “wrap” library calls in try… catch() blocks like this:

SLIDE 19

How to Start A1?

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Getting Started

Copy A0 into A1 (or create a new project in a1/ directory)
Open your project in IntelliJ, and make sure it builds!
Make sure that you have a single Java file: FindFiles.java
i.e. class is named FindFiles

Structure

1. Read the command line parameters and options

1. Check that they are valid

2. Get the files in the directory that match the given filename or regular expression

3. Print the absolute path of the found files

SLIDE 20

A1 Classes

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Java has extensive libraries that cover any functionality you will need.
Useful classes for A1:
java.lang.String
matches()
equals (String) // do NOT use == since that compares objects
java.io.File
isDirectory()
getParentFile()
listFiles()

See Sample Code!

1. Intro project

SLIDE 21

Packaging Java Applications

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How do you deploy a more complex Java application?

1. Give out all of the .class files (could be hundreds of them!)
i.e. email, flash drive etc.
2. Use `jar’ utility to package the .class files into a single file
Basically a ZIP file with some metadata. e.g. Main.jar
User can execute from the JAR file directly.

e.g. java –jar Main.jar

3. Use a third-party utility to build a standalone EXE file (e.g. Launch4j)

For this course, we’re not going to package our apps.

SLIDE 22

Coding w. an IDE

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We’re using IntelliJ 2019.3 in this course. This is an Integrated

Development Environment (IDE) that provides:

Better code navigation
Code completion
Debugging
Integration with API docs
Integration with testing framework
Simplified build framework
For your assignments, you are required to submit source code AND

an IntelliJ project that compiles and builds your code.

This is critical when we start building more complex applications