Computer Programming 12

Mr. Jean

March 19th, 2013

The plan:

• Video clip of the day

• Why Java

• More simple programs

2.1 Why Java?

• Java is the fastest growing programming language in the world.

• Java is a modern object-oriented programming language.

• Java has benefited by learning from the less desirable features of early object-oriented programming languages.

2.1 Why Java?

• Java is ideally suited to develop distributed, network-based applications because it:

– Enables the construction of virus-free, tamper-free systems (security)

– Supports the development of programs that do not overwrite memory (robust)

– Yields programs that can be run on different types of computers without change (portable)

2.1 Why Java?

• Java supports advanced programming concepts such as threads.

– A thread is a process that can run concurrently with other processes.

• Java resembles C++, the world’s most popular industrial strength programming language.

• Java however, runs more slowly than most modern programming languages because it is interpreted.

2.2 The Java Virtual Machine and Byte Code

• Java compilers translate Java into pseudomachine language called java byte code.

• To run java byte code on a particular computer, a Java virtual machine (JVM) must be installed.

2.2 The Java Virtual Machine and Byte Code

• A Java virtual machine is a program that acts like a computer. It is called an interpreter.

• Disadvantage:– Runs more slowly than an actual

computer• To combat slower processing, some JVMs

translate code when first encountered. This is known as just-in-time compilation (JIT).

2.2 The Java Virtual Machine and Byte Code

• Advantages:

– Portability. Any computer can run Java byte code.

– Applets. Applets are small Java programs already translated into byte code.

• Applets run in a JVM incorporated in a web browser• Applets can be decorative (like animated characters on

a web page.)• Applets can be practical (like continuous streams of

stock market quotes.)

– Security. It is possible to limit the capabilities of a Java program since it runs inside a virtual machine.

2.3 Choosing a User Interface Style

• There are two types of user interfaces available to use to create Java programs.

– Graphical User Interface (GUI)– Terminal I/O interface

• Figure 2-1 illustrates both interfaces used to create the same program.

2.3 Choosing a User Interface Style

2.3 Choosing a User Interface Style

• There are 3 reasons for beginning with terminal I/O:

– It is easier to implement than a GUI– There are programming situations that

require terminal I/O– Terminal-oriented programs are similar in

structure to programs that process files of sequentially organized data. (What is learned here is easily transferred to that setting.)

2.4 Hello World

• Figure 2-2 displays the results of a small Java program, entitled “hello world”

2.4 Hello World

• A program is a sequence of instructions for a computer.

• The following is the bulk of instructions, or source code, for the “hello world” program.

2.4 Hello World

• Sending messages to objects always takes the following form:

<name of object>.<name of message>(<parameters>)

2.4 Hello World

• The original “hello world” program needs to be embedded in a larger framework defined by several additional lines of code, in order to be a valid program.

2.5 Edit, Compile, and Execute

• Figure 2-3 illustrates the edit, compile and execute steps.

2.5 Edit, Compile, and Execute

• Development environments:– Unix

• standard text editor• command line activation of compiler and JVM

– DOS, using Microsoft Windows and NT OS• notepad text editor• command line activation of compiler and JVM

from a DOS window– Integrated development environment, using

Windows, NT, or MAC OS• Examples: Symantec’s Visual Café, Microsoft’s

Visual J++, or Borland’s J Builder

2.5 Edit, Compile, and Execute

• Preparing your development environment:

– Create a directory, open a terminal window, use the cd command to move to your new directory

– Open notepad, create the file HelloWorld.java, type in the lines of code

– Save the file, go back to the terminal window, compile the program

– Run the program

2.5 Edit, Compile, and Execute

• The following figures illustrate the steps necessary for preparing your development environment.

2.5 Edit, Compile, and Execute

2.5 Edit, Compile, and Execute

Today’s Task:

• Create a program which completes the following task.

• Output Display needed:

a = 30b = 40a * b = 1200

Today’s Task:

• Build Program #2

• Build Program #3

• Using what we have seen in programs #2 & #3, build a program which successfully asks for your name, what class your are in and today’s date.