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Introduction to Java
Tonga Institute of Higher Education
Programming Basics
Program – A set of instructions that a computer uses to do something.
Programming / Develop – The act of creating or changing a program
Programmer / Developer – A person who makes a program
Run / Execute – The act of using a program
Every program was created by someone Computers use special languages Programmers use special languages to create or change a
program
Machine Language
Machine language – A language understood by computers
When programs are run, machine language is used
Machine languages are almost impossible for humans to understand
Every operating system (OS) has its own machine language Windows Linux Macintosh
Hardware
Machine Language
High Level Language
C++ Java VB .NET
High Level Languages
High Level Language - A programming language that is understandable by people
This enables a programmer to write programs
High level languages must be translated into machine language before running on a computer
Hardware
Machine Language
High Level Language
C++ Java VB .NET
Compilers and Interpreters
There are two main ways to change programs written in a high level language to machine language:
1. Use a compiler
2. Use an interpreter
Source Code – Code written in a programming language by a developer.
Compilers Compiler – A program that transforms code from
one format to another
Source code
Linux compiler
Windows compiler
Macintosh compiler
Linux code
Macintosh code
Windows code
Machine LanguageHigh Level Language
Windows
Linux
Macintosh
Compilers vs. Interpreters
Advantages Programs run faster
Disadvantages Platform dependent - Programs only work on a
specific operating system. Windows Linux Macintosh
Compiling a large program may take a long time
Interpreters
Interpreter – A program that translates and executes code
Usually, interpreters translate and execute source code.
Source Code Interpreter
High Level Language Code for Windows, Linux and Macintosh
Machine Language
Windows,Linux and Macintosh
Interpreters vs. Compilers
Advantages Platform Independent. Don’t need to compile anything.
Disadvantages The interpreter program must be installed on the
computer that the program will run on Slower execution You should only use services available on all
platforms. Example: Windows has a cool sound library, but you can’t
use it because it won’t run on Macintosh
Review
Give a short description of:Machine LanguageHigh Level Language
Give a short explanation of how an compiler is different from an interpreter
Introduction to Java
Java is a programming language created by Sun Microsystems.
Java.sun.com Many programmers use Java Java is an object oriented language.
Java Setup
Steps to install Java Required
1. Install the Java Software Development Kit (SDK) Find it at http://java.sun.com. Java 2 Standard Edition
Not Required but good1. Install Java Documentation
2. Install Integrated Development Environment (IDE) IDE – A program that helps you to write code
Demonstration
Sun WebsiteJava DocumentationJava IDE
How Does Java Work? Java uses a compiler and interpreter! You can compile the program once and run it on
each platform with an interpreter
Source code
Java Compiler
Byte Code
Windows
Macintosh
Linux
Java Interpreter
Windows
Linux
Macintosh
How to Create a Java Program
1. Create a source file.
2. Use the Java compiler to create byte code.
3. Run the byte code using the Java interpreter.
Create a Source File
Write Java source code and save it in a file
Use a text editor or Integrated Development Environment (IDE).
Filename extension: .java
Demonstration
Create a source file
Use the Java Compiler to Create Byte Code Source code is compiled by a Java compiler to byte
code. Byte Code
A file that can run on any computer that has a Java Interpreter Filename extension: .class
Compiler program: javac.exe
Java Compile
r
Javac.exe
Source Codevoid main () … ??this$0?!...
Byte Code
.java .class
Use the Java Compiler to Create Byte Code Important Details
Javac.exe <filename>.java Ex: Javac HelloWorld.java
A .class file is made for every class in the file. Common Errors
Unable to find the Compiler - Something is wrong with your Java setup. Windows can’t find the Java compiler.
Is your access to Javac.exe and Java.exe setup properly? Invalid Flag – One of the inputs are wrong.
Did you include the .java extension? Are you using the right file?
Demonstration
Compiling Source Code
Run the Byte Code Using the Java Interpreter Java Virtual Machine (JVM) – A program which interprets Java
programs that have been compiled into byte-code and usually stored in a ".class" file.
Interpreter performs actions Creates windows Prints Etc.
Interpreter program: java.exe
Java Interpret
er
Java.exe
Byte Code??this$0?!...
.class
Run the Byte Code Using the Java Interpreter Important Details
Java.exe <class name> Ex: Java HelloWorld
The class name must have the correct case!
Common Errors NoClassDefFoundError – The class can’t be found.
Is your class in the correct directory? Are you using the correct case?
Demonstration
Running Byte Code