Download CSIS-120: Java Intro

Chapter 1
CSIS-120: Java Intro
What is Programming?
 A: It is what makes computer so useful.
 The flexibility of a computer is amazing
 Write a term paper (Word processing program)
 Balance checkbook (Accounting program)
 Play a game (Games are programs)
 Post on Facebook (Facebook is program)
 Programming  Computer Programs
What is a Computer Scientist?
 Somebody who can write programs to solve lots of
different problems.
 You don’t need to program to use programs
 But, often times you need to program to solve an array of
different problems.
Computer Hardware
 Hasn’t changed as much as you would think.
 See Diagram on page 6
 Programming has improved just as much as the
hardware.
Evolution of programming
 Early 60’s
 Specify instructions in binary
 01010101101010101
 Late 60’s to 70’s
 Machine language
 Instruction codes and value in hexidecimal
 2F 4A0
 56 C13
Evolution of programming
 70’s to Today
 Assembly language (more general, more human readable – get
translated into machine language)
 SET r1, 10 ; r1 will take the place of i
SET r2, 1 ; r2 will hold the value to subtract each time
LOOP1TOP:
SUB r1, r1, r2 ; subtract one from r1
CMP r1, r0
JMP NEQ, LOOP1TOP ;
 Late 70’s to Today
 High level language
 Designed for humans to “easily” read/write
 C++, Java, etc.
Evolution of programming
 90’s to Today
 Graphical languages
 makes it even “easier” to program
 Alice, Labview, etc.
 But in the end it all get compiled to binary
 High Level Language 
Assembly Code 
Machine Instructions  Binary
Compilation
 High-level languages are compiled into machine
language.
 A compiler itself is a program that simply translates from
high-level lanaguage to low-level.
 Most compilers create machine language for a specific
type of operating system/computer (called a platform)
 PC Platform
 Mac Platform
 Unix Platform
Compilation & Java
 A Java compiler creates “machine language” (Java
Byte Code) that can be run on any type of computer.
 The computer just needs a Java Virtual Machine (JVM)
 The JVM is just a program that can execute Java Byte code
for a specific computer.
 In theory, your compiled program can run on any computer.
Traditional Compilation (C++)
 The compiler eventually creates machine language for a
specific operating system/computer platform (Windows,
Mac, Linux, etc.)
 If you wish to run you program on a PC and a Mac, you
need two compilers and need to compile two different
running programs.
 In contrast, a Java program just needs to be compiled
once.
 But, the PC and Mac will both need installed JVMs (Java
Virtual Machines)
Java is still very popular
 Platform independence: Compiled programs can run on
any device with a JVM installed.
 Java Enterprise Edition EE
 Java works well with the Internet & WWW
 Rather than run programs on your computer, Java allows
you to easily create programs that can run on a web server.
 Java Server Pages (JSP) can “call” Java programs.
 Thus, complex programs can be run from web-enabled
devices (iPhone, Droid Phone, etc.) without actually
“executing” the program locally
 programs execute on the server.
Let’s start with a most basic program
 Traditionally, the ‘hello world’ program is the first one
taught in most classes/texts.
HelloPrinter.java
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public class HelloPrinter
{
public static void main(String[] args)
{
// Display a greeting in the console window
System.out.println("Hello, World!");
}
}
Program Run:
Hello, World!
The Structure of a Simple Program: Class Declaration
• Classes are the fundamental building blocks of
Java programs:
public class HelloPrinter
starts a new class
• A class defines a “reusable” programming
object.
• In a computer game, the classes might include
things like
public class Zombie
public class RocketLauncher
Each class goes in a .java file
• Every source file can contain at most one public
class
• The name of the public class must match the
name of the file containing the class:
• Class HelloPrinter must be contained in a file
named HelloPrinter.java
The Structure of a Simple Program: main Method
• Every Java application contains a class with a main
method
• When the application starts, the instructions in the main
method are executed
• public static void main(String[] args)
{
. . .
}
declares a main method
The Structure of a Simple Program: Comments
• The first line inside the main method is a comment:
// Display a greeting in the console window
• Compiler ignores any text enclosed between //
and end of the line
• Use comments to help human readers understand
your program
The Structure of a Simple Program: Statements
• The body of the main method contains statements
inside the curly brackets ({})
• Each statement ends in a semicolon (;)
• Statements are executed one by one
• Our method has a single statement:
System.out.println("Hello, World!");
which prints a line of text:
Hello, World
The Structure of a Simple Program: Method Call
• System.out.println("Hello, World!");
is a method call
• A method call requires:
1. The object that you want to use (in this case, System.out)
2. The name of the method you want to use (in this case, println)
3. Parameters enclosed in parentheses (()) containing any other
information the method needs (in this case, "Hello, World!")
Syntax 1.1 Method Call
The Structure of a Simple Program: Strings
• String: a sequence of characters enclosed in
double quotation marks:
"Hello, World!"
Self Check 1.10
How would you modify the HelloPrinter program
to print the words "Hello," and "World!" on two
lines?
Answer:
System.out.println("Hello,");
System.out.println("World!");
Self Check 1.12
What does the following set of statements print?
System.out.print("My lucky number is");
System.out.println(3 + 4 + 5);
Editing a Java Program
• Use an editor to enter and modify the program text
• Java is case-sensitive
• Be careful to distinguish between upper- and lowercase letters
• Lay out your programs so that they are easy to read
Compiling and Running a Java Program
• The Java compiler translates source code into
class files that contain instructions for the Java
virtual machine
• A class file has extension .class
• The compiler does not produce a class file if it has
found errors in your program
• The Java virtual machine loads instructions from
the program's class file, starts the program, and
loads the necessary library files as they are
required
HelloPrinter in a Console Window
HelloPrinter in an IDE
From Source Code to Running Program
Self Check 1.14
What do you expect to see when you load a class
file into your text editor?
Errors
• Compile-time error: A violation of the
programming language rules that is detected by
the compiler
• Example:
System.ou.println("Hello, World!);
• Syntax error
• Run-time error: Causes the program to take an
action that the programmer did not intend
• Examples:
System.out.println("Hello, Word!");
System.out.println(1/0);
• Logic error
Algorithms
• Algorithm: A sequence of steps that is:
• unambiguous
• executable
• terminating
• Algorithm for deciding which car to buy, based on total costs:
For each car, compute the total cost as follows:
annual fuel consumed = annual miles driven / fuel efficiency
annual fuel cost = price per gallon x annual fuel consumed
operating cost = 10 x annual fuel cost
total cost = purchase price + operating cost
If total cost1 < total cost2
Choose car1
Else
Choose car2
Pseudocode
• Pseudocode: An informal description of an algorithm:
• Describe how a value is set or changed:
total cost = purchase price + operating cost
• Describe decisions and repetitions:
For each car
operating cost = 10 x annual fuel cost
total cost = purchase price + operating cost
Use indentation to indicate which statements should be selected
or repeated
• Indicate results:
Choose car1
Program Development Process