Download The Central Processing Unit

Introduction to Programming
and Java
The Central Processing Unit
• The speed of a CPU is controlled by the system clock which
generates an electronic pulse at regular intervals
• One “machine cycle” per pulse which performs a part of a machine
language command, for example
• move info in register A to memory location 58467
• add contents of register A to register B
• Computers generate billions of pulses per second
• What’s a machine language command?
2
Machine Language Commands
• A machine language command
is the most basic command
stored in a computer’s
memory.
• For example:
– 10110000 01100001
• A machine language program
is a sequence of hundreds of
such commands.
• Sound like fun?
• Early computer programmers
didn’t like dealing with machine
language so they invented
assembly language.
Assembly Language Commands
• A single assembly language
command corresponds to a single
machine language command but is
easier for a programmer to
read/write/understand
• For example
– move #061,1207
• A assembly language program is a
sequence of hundreds of such
commands.
• Sound like fun?
• It’s better, but early computer
programmers didn’t like dealing with
assembly language much either so
they invented high level language.
finit
mov cx,8
mov al,[Y]
or
al,al
jnz LoadX
fld1
jmp Exit
LoadX:
fld [X]
fld [X]
dec cx
shl al,1
High Level Language Commands
• A high level language command can
correspond to several assembly language
commands
• High level languages also allow
programmers to use “names” instead of
memory addresses
• For example:
cost = (price – discount) * (1 + taxrate);
• A high level language program is a
sequence of many such commands.
• Sound like fun?
• Yes!!!!!!!!!!!!!!!!
Grace Hopper
Program Translation I
• Each type of CPU executes
only a particular machine
language
high level
source code
• A high level language program
must be translated into
machine language before it
can be executed
Compiler
• A compiler is a software tool
which translates source code
into a specific target language
8086 machine
code
8086 CPU
6
Program Translation 2
• Each type of CPU executes
only a particular machine
language
high level
source code
• A high level language program
must be translated into
machine language before it
can be executed
• A interpreter is a software tool
which translates source code
into a specific target language
one line at a time, as needed
Interpreter
8086 CPU
7
High Level Languages
• There are hundreds of
different high level languages
• Each has its strengths and
weaknesses
• We’ll use Java in this course
• And there are even “higher”
level languages called 4th
generation languages
8
Java
• A programming language specifies the words and symbols that we
can use to write a program
• A programming language employs a set of rules that dictate how the
words and symbols can be put together to form valid program
statements
• The Java programming language was created by Sun
Microsystems, Inc.
• It was introduced in 1995 and it's popularity has grown quickly since
Java Program Structure
• In the Java programming language:
– A program is made up of one or more classes
– A class contains one or more methods
– A method contains program statements
• These terms will be explored in detail throughout the course
• A Java application always contains a method called main
• See Lincoln.java (page 29)
Java Program Structure
//
comments about the class
public class MyProgram
{
class header
class body
Comments can be placed almost anywhere
}
11
Java Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
method header
}
}
12
Comments
• Comments in a program are called inline documentation
• They should be included to explain the purpose of the program
and describe processing steps
• They do not affect how a program works
• Java comments can take three forms:
// this comment runs to the end of the line
/*
this comment runs to the terminating
symbol, even across line breaks
/** this is a javadoc comment
*/
*/
13
Identifiers
• Identifiers are the words a programmer uses in a program
• An identifier can be made up of letters, digits, the underscore
character ( _ ), and the dollar sign
• Identifiers cannot begin with a digit
• Java is case sensitive - Total, total, and TOTAL are
different identifiers
• By convention, programmers use different case styles for different
types of identifiers, such as
– title case for class names - Lincoln
– upper case for constants - MAXIMUM
14
Identifiers
• Sometimes we choose identifiers ourselves when writing a program
(such as Lincoln)
• Sometimes we are using another programmer's code, so we use the
identifiers that he or she chose (such as println)
• Often we use special identifiers called reserved words that already
have a predefined meaning in the language
• A reserved word cannot be used in any other way
Java Reserved Words
abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while
16
White Space
• Spaces, blank lines, and tabs are called white space
• White space is used to separate words and symbols in a program
• Extra white space is ignored
• A valid Java program can be formatted many ways
• Programs should be formatted to enhance readability, using
consistent indentation
• See Lincoln2.java
• See Lincoln3.java
Fall 2010 --- Do Lab Here
17
Java Translation
• The Java compiler (javac) translates Java source code into a special
representation called bytecode
• Java bytecode is not the machine language for any traditional CPU
• Another software tool (java), called an interpreter, translates
bytecode into machine language and executes it
• Therefore the Java compiler is not tied to any particular machine
• Java is considered to be architecture-neutral
18
Java Translation
Java source
code
Java
compiler
(javac)
Java
bytecode
Bytecode
interpreter
(java)
Bytecode
compiler
Machine
code
19
Program Development
• The mechanics of developing a program include several activities
– understanding what the program is supposed to do
– designing the program
– writing the program in a specific programming language (such as
Java)
– translating the program into a form that the computer can
execute
– investigating and fixing various types of errors that can occur
• Computer programmers didn’t like dealing with all of this at the
“command line” level, so they invented software tools that can be
used to help with many parts of this process
Development Environments
• There are many programs that support the development of Java
software, including:
–
–
–
–
–
–
–
Sun Java Development Kit (JDK)
Sun NetBeans
IBM Eclipse
Borland JBuilder
MetroWerks CodeWarrior
BlueJ
jGRASP
• Though the details of these environments differ, the basic
compilation and execution process is essentially the same
Syntax and Semantics
• The syntax rules of a language define how we can put together
symbols, reserved words, and identifiers to make a valid program
sum = value1 + value2;
// correct syntax
product = (value1)(value2); // incorrect syntax
• The semantics of a program statement define what that statement
means (its purpose or role in a program)
• A program that is syntactically correct is not necessarily logically
(semantically) correct
sum = value1 - value2;
// logic error?
• A program will always do what we tell it to do, not what we meant to
tell it to do
22
Errors
• A program can have three types of errors
• The compiler will find syntax errors and other basic problems
(compile-time errors)
– If compile-time errors exist, an executable version of the program
is not created
• A problem can occur during program execution, such as trying to
divide by zero, which causes a program to terminate abnormally
(run-time errors)
• A program may run, but produce incorrect results, perhaps using an
incorrect formula (logical errors)
23
Basic Program Development
Edit and
save program
errors
errors
Compile program
Execute program and
evaluate results
Problem Solving
• The purpose of writing a program is to solve a problem
• Solving a problem consists of multiple activities:
– Understand the problem
– Design a solution
– Consider alternatives and refine the solution
– Implement the solution
– Test the solution
• These activities are not purely linear – they overlap and interact
Problem Solving
• The key to designing a solution is breaking it down into manageable
pieces
• When writing software, we design separate pieces that are
responsible for certain parts of the solution
• An object-oriented approach lends itself to this kind of solution
decomposition
• We will dissect our solutions into pieces called classes and objects
• An application/program can use
– the primitive Java language
– the Java library classes and objects (and their methods)
– “homemade” classes and objects (and their methods)
An example using (mostly) the
primitive language
//*********************************************************
// Sum01.java
Author: Joyce
//
// Demonstrates a simple Java application.
//*********************************************************
public class Sum01
{
public static void main (String[] args)
{
int value1, value2;
int sum;
value1 = 7; value2 = 4;
sum = value1 + value2;
System.out.println ("The sum of " + value1 + " and " +
value2 + " is " + sum);
}
}
Java Library Classes
• Java 2 Platform Standard Edition 5.0
• The API Specification (see link off Joyce’s CSC
1051 page)
• There are almost 3,000 classes
• Packages/Sub-packages are for organizational
purposes, for example
– awt: abstract windowing toolkit
– lang: fundamental to the Java language
Static Methods
• can be called directly through the class
• not the “common” approach .. but the
easiest to understand
• for example, all the methods of the Math
class are static:
– abs
– pow
– sqrt
–…
An example
using some
static methods
from the Java
library Math
class
//*********************************************************
// MathDemo.java
Author: Joyce
//
// Demonstrates using static methods.
//*********************************************************
public class MathDemo
{
public static void main (String[] args)
{
int value1, value2;
int sum;
value1 = 7; value2 = 4;
sum = value1 + value2;
System.out.println (value2 + " raised to the " + value1 +
" power is " + Math.pow(value2, value1));
static method call
System.out.println ("The square root of the sum of " +
value1 + " and " + value2 + " is " + Math.sqrt(sum));
}
}
static method call
Object-Oriented Programming
• Java is an object-oriented programming language
• As the term implies, an object is a fundamental entity in a Java
program
• Objects can be used effectively to represent real-world entities
(among other things)
• For instance, an object might represent a specific person’s bank
account
• Each bank account object handles the processing and data
management related to that account
© 2007 Pearson Addison-Wesley. All rights reserved
2-31
Objects
•
An object has:
– state - descriptive characteristics
– behaviors - what it can do (or what can be done to it)
•
The state of a bank account includes its account number and its current
balance
•
The behaviors associated with a bank account include the ability to make
deposits and withdrawals
•
Note that the behavior of an object might change its state
•
Note that the state of an object might affect its behaviour
© 2007 Pearson Addison-Wesley. All rights reserved
2-32
Classes and Objects
• An object is defined by a class
• A class is the blueprint of an object
– Typically state is maintained in a set of private variables
– Typically public methods define the behaviors of the object
• A class represents a concept, and an object represents
the embodiment of that concept
• Multiple objects can be created from the same class
© 2007 Pearson Addison-Wesley. All rights reserved
2-33
Objects and Classes
A class
(the concept)
Bank Account
private double balance
public double deposit
(double amount)
objects
(the realization)
John’s Bank Account
balance: $5,257
Bill’s Bank Account
balance: $1,245,069
Mary’s Bank Account
balance: $16,833
© 2007 Pearson Addison-Wesley. All rights reserved
2-34
{
Account acct1 = new Account ("Ted Murphy", 72354, 102.56);
Account acct2 = new Account ("Jane Smith", 69713, 40.00);
Account acct3 = new Account ("Edward Demsey", 93757, 759.32);
acct1.deposit (25.85);
double smithBalance = acct2.deposit (500.00);
System.out.println ("Smith balance after deposit: " +
smithBalance);
System.out.println ("Smith balance after withdrawal: " +
acct2.withdraw (430.75, 1.50));
acct1.addInterest();
acct2.addInterest();
acct3.addInterest();
System.out.println ();
System.out.println (acct1);
System.out.println (acct2);
System.out.println (acct3);
}
public class Experiment04
{
public static void main (String[] args)
{
...
PairOfDice dice1 = new PairOfDice();
PairOfDice dice2 = new PairOfDice();
NumberStats stats1 = new NumberStats();
NumberStats stats2 = new NumberStats();
object creation
Scanner scan= new Scanner (System.in);
DecimalFormat fmt= new DecimalFormat ("0.###");
System.out.print("See result of each dice roll? (Y = Yes) > ");
boolean trace = scan.nextLine().equalsIgnoreCase("Y");
...
System.out.println("\nDice 1: " + dice1.maxString());
...
dice2 = new PairOfDice(numSides1, numSides2);
stats1.submit(dice1.roll());
...
object use
Inheritance
• One class can be used to derive another via inheritance
• Classes can be organized into hierarchies
Account
Charge
Account
Bank
Account
Savings
Account
Checking
Account