Chapter 1

• Early computers and machine language

– Any computer can directly understand only its own machine language

• Assembly languages

– Translated directly into machine language by an assembler

• High-level languages

– Types of translators: Compilers and Interpreters

– History of C and C++

• The Internet and the WWW

– Java and platform independence

• Typical Java Development Environment

The Java environment

• A text editor is used to record the high level java program in ASCII code

– We will use BlueJ

– A file with .java extension is created; it is in ASCII code

• A java compiler translates the .java file into bytecode

– The compiler we use is the JDK (Java Development Kit)

– A file with .class extension is created; it is in bytecode

• A bytecode interpreter translates the .class file into the machine language for the its specific machine

– The bytecode must be loaded into RAM before it is interpreted

– As the bytecode is loaded, the bytecode verifier checks to make sure it does not violate any security restriction.

The Java Platform summary

• First the source code is compiled into bytecode.

• On the local machine an interpreter reads the bytecode and translates it into machine language for that specific machine.

– It is easier to write an interpreter for the Java bytecodes than it is to write a compiler for the Java source code

• This interpreter is included in modern browsers so that they can interpret bytecodes (i.e. run an applet)

Applications and Applets

• Applets

– programs that can be embedded in HTML documents.

– HTML has tags specifically designed for Java applets

• Applications

– Traditional programs that can run stand-alone from the command line or a GUI

– In Java, a main method is included in a class to make it an application

Getting started with Java

• The Java Development Kit (JDK) is provided free from Sun, who developed Java

• The user interface to the JDK is not great

• BlueJ is a editor that uses the JDK; it provides a GUI, designed especially for education

• There is a BlueJ tutorial (31 pages) provided by the developers of BlueJ, available for download free

– It is in Adobe Acrobat format.

Downloads

• If you have a machine, you should download the JDK and BlueJ

• The versions on the disk supplied with your text of the JDK and BlueJ are not the latest versions

• The latest versions, which can be downloaded from the Internet.

• See Resources on the home page for download links

Test-Driving a Java Application

• Page 16-20 of your text

• Your text tells you how to run the application using the command line

• An alternate way is to use BlueJ

– Open BlueJ

– Click on Project, then Open non BlueJ

– Find the program

• Use appJ instead of the program in Chapter 1

• The Chapter 1 version has only the .class files, not the .java files which BlueJ needs

– Compile the program

• To execute a program in BlueJ, you must know which class contains the main method

• Since it stated on the command line with ATMCaseStudy, that is the one