Chapter 1

Introduction

Chapter Goals

• To understand the activity of programming
• To learn about the architecture of computers
• To learn about machine code and high level programming languages
• To become familiar with your computing environment and your compiler
• To compile and run your first Java program
• To recognize syntax and logic errors

Prerequisites

• Computer savvy (file management, text editing)
• Problem solving skills
• Time management
• High school math (algebra, trigonometry)
• No prior programming background required

What Is Programming?

• Computers are programmed to perform tasks
• Different tasks = different programs
• Program
  • Sequence of basic operations executed in succession
  • Contains instruction sequences for all tasks it can execute
• Sophisticated programs require teams of highly skilled programmers and other professionals

Self Check

1. What is required to play a music CD on a computer?
2. Why is a CD player less flexible than a computer?
3. Can a computer program develop the initiative to execute tasks in a better way than its programmers envisioned?

Answers

1. A program that reads the data on the CD and sends output to the speakers and the screen.
2. A CD player can do one thing–play music CDs. It cannot execute programs.
3. No–the program simply executes the instruction sequences that the programmers have prepared in advance.

The Anatomy of a Computer

• Central processing unit
  • Chip
  • Transistors
• Storage
  • Primary storage: Random-access memory (RAM)
  • Secondary storage: e.g. hard disk
  • Removable storage devices: e.g.: floppy disks, tapes, CDs
• Peripherals
• Executes very simple instructions
• Executes instructions very rapidly
• General purpose device

Central Processing Unit

A Memory Module with Memory Chips

A Hard Disk

A Motherboard

Schematic Diagram of a Computer

The ENIAC

Self Check

4. Where is a program stored when it is not currently running?
5. Which part of the computer carries out arithmetic operations, such as addition and multiplication?

Answers

4. In secondary storage, typically a hard disk.
5. The central processing unit.

Machine Code

• Java Virtual Machine (JVM) – a typical sequence of machine instructions is:
  
  1. Load the contents of memory location 40.
  2. Load the value 100.
  3. If the first value is greater than the second value, continue with the instruction that is stored in memory location 240.
  Machine instructions are encoded as numbers:
  21 40
  16 100
  163 240
• Compiler translates high-level language to machine code

Self Check

6. What is the code for the Java virtual machine instruction "Load the contents of memory location 100"?
7. Does a person who uses a computer for office work ever run a compiler?

Answers

6. 21 100
7. No–a compiler is intended for programmers, to translate high-level programming instructions into machine code.

The Java Programming Language

• Simple
• Safe
• Platform-independent ("write once, run anywhere")
• Rich library (packages)
• Designed for the internet

Applets on a Web Page

Self Check

8. What are the two most important benefits of the Java language?
9. How long does it take to learn the entire Java library?

Answers

8. Safety and portability.
9. No one person can learn the entire library–it is too large.

Becoming Familiar with your Computer

• Log in
• Locate the Java compiler
• Understand files and folders
  • Programs are kept in files
  • File: a collection of items of information that are kept together
  • Files have names, and the rules for legal names differ from one system to another
  • Files are stored in folders or directories; these file containers can be nested
• Write a simple program (later)
• Save your work
  • Develop a strategy for keeping backup copies of your work

A Shell Window

An Integrated Development Environment

Nested Folders

Self Check

10. How are programming projects stored on a computer?
11. What do you do to protect yourself from data loss when you work on programming projects?

Answers

10. Programs are stored in files, and files are stored in folders or directories.
11. You back up your files and folders.

File HelloTester.java

Output

   Hello, World!

HelloTester in a Console Window

HelloTester in an IDE

A Simple Program

• public class ClassName
• public static void main(String[] args)
• // comment
  
• Method call
  
• System class
• System.out object
• println method

Syntax 1.1: Method Call

object.methodName(parameters)

System.out.println("Hello, Dave!");

Self Check

12. How would you modify the HelloTester program to print the words "Hello," and "World!" on two lines?
13. Would the program continue to work if you omitted the line starting with //?
14. What does the following set of statements print?

    System.out.print("My lucky number is");
    System.out.println(3 + 4 + 5);

Answers

12. System.out.println("Hello,");
    System.out.println("World");
13. Yes–the line starting with // is a comment, intended for human readers. The compiler ignores comments.
14. The printout is My lucky number is12. It would be a good idea to add a space after the is.

Errors

• Syntax errors
  System.ouch.print(". . .");
  System.out.print("Hello);
• Detected by the compiler
• Logic errors
  System.out.print("Hell");
• Detected (hopefully) through testing

Self Check

15. Suppose you omit the // characters from the HelloTester.java program but not the remainder of the comment. Will you get a compile-time error or a run-time error?
16. How can you find logic errors in a program?

Answers

15. A compile-time error. The compiler will not know what to do with the word display.
16. You need to run the program and observe its behavior.

The Compilation Process

The Edit-Compile-Test Loop

Self Check

17. What do you expect to see when you load a class file into your text editor?
18. Why can't you test a program for run-time errors when it has compiler errors?

Answers

17. A sequence of random characters, some funny-looking. Class files contain virtual machine instructions that are encoded as binary numbers.
18. When a program has compiler errors, no class file is produced, and there is nothing to run.