introduction to programming with java
DESCRIPTION
Introduction to Programming with Java. AP Computer Science ASFA. What is an Object?. A person, place, or thing That knows something about itself Has data (attributes, fields) A cashier has a id, name, and a password And can do something Has operations (methods) - PowerPoint PPT PresentationTRANSCRIPT
Introduction to Programmingwith Java
AP Computer ScienceASFA
Intro-OO 2
What is an Object?
• A person, place, or thing– That knows something about
itself• Has data (attributes, fields)• A cashier has a id, name, and a
password
– And can do something• Has operations (methods)• A cashier can total the items,
take payment, make change
Intro-OO 3
What is a Class?
• The type of an object – The way we classify
an object• “The Idiot” by
Dostoevsky is a book• “War and Peace” by
Tolstoy is a book• Caitlin is a cashier• Kheri is a cashier
• Grouping of objects with the same data and operations
• We will use the Java language to model our objects on the computer
• Cashier has attributes:– Name – Id number
• Cashier can perform:– Make change– Calculate order total
This would be modeled in Java as a Cashier class with memory set aside to store:– Name – Id number
And instructions on how to perform:– Make change– Calculate order total
Alexander and Jefferson are both Cashier objects
Alexander has a different name and id number than Jefferson, but they both make change the same way
Now Let’s Look at the Small Steps
• How are we going to make this happen through a computer program?
Part 1
What is a computer?
What is this programming thang?
What is Java?
What is a Computer?
• A device that performs high-speed mathematical and/or logical operations or that assembles, stores, correlates, or otherwise processes information.
• The first computers were people – who did computations
Why Do Computers Keep Getting Cheaper?
• The number of transistors (a major component of the brain of a computer) at the same price doubles every 18 months– making computers faster, smaller, and
cheaper over time• This notion is know as Moore’s Law
– For Gordon Moore, a founder of Intel• This “Law” has held true for decades
– And is predicted to hold true at least one more
What are Computers Good At?
• Doing calculations and comparisons• Producing the same answer every time
– Like calculating the sum of hundreds of numbers
• Storing information – They don’t forget information
• Looking up information quickly– Search through a phone book to find the
customer name for a phone number
What is Programming?• Creating detailed
instructions that a computer can execute to accomplish some task.– Like writing a recipe
for your favorite dish– Or giving someone
directions to your house
– Or making a robot do what you want
Early Programming
• Early computers required the programmer to set switches and move wires– Which represented a
series of 1’s and 0’s
• Later computers were programmed using punched cards
Language Evolution
• Early languages were based on how to do instructions on each machine– 1’s and 0’s to add, subtract, read, store, etc
• Assembler allowed you to write programs using names for instructions and memory– But still translated into machine language
• Higher-level languages– Are compiled into machine language or virtual
machine language (Java)
Java
• Developed at Sun in the early 1990s– Invented by James Gosling
• Similar to C++ in syntax but easier to use– Less likely to crash– Automatic memory management
• Cross-platform, object-oriented language• One of the fastest adopted technologies of
all time• Current favorite language, for now
Which Language?
• All high-level languages are eventually translated into machine language
• You can write the same program in any language– The computer doesn’t care what high-level
language you use• The language matters to the programmer
– How long does it take to write the program?– How hard is it to change the program?– How long does it take to execute?
Why Don’t We Just Use English?
• English is good for communication between two intelligent humans– Even then we sometimes don’t
understand
• Computers are very stupid– They basically know how to
add, compare, store, and load– Programs are very detailed
instructions• Everything must be precise
and unambiguous
Programming Exercise
• Write down instructions for how to make a paper airplane
• Have your partner read the directions and make an airplane– stop anytime anything
isn’t clear and ask for clarification
Summary – Part 1
• Computers perform calculations and comparisons
• A program is a series of instructions to a computer
• Programming has changed from moving wires to writing textual programs that can be stored and executed several times
• Java is a high level popular programming language
Part 2
How does the computer do it?
Parts of a Computer• User Interface
– monitor (screen), mouse, keyboard, printer
• Brain - Central Processing Unit – can do math and logic
operations• Memory - Storage
– main - RAM– secondary – Disks,
CD-ROMs, DVDs
CPU – Brain of the Computer
• Arithmetic/Logic Unit (ALU)– Does math and logic
calculations on numbers in registers
• Control Unit– Reads instructions
from memory and decodes and executes them using the ALU
345
263Add register A to register B
608 Store the value in register C into memory location320843202
Fetch, Decode, Execute Cycle
• The control unit reads (fetches) an instruction from memory
• The control unit decodes the instruction and sets up the hardware to do the instruction – like add the values in the A and B registers
and put the result in the C register• The instruction is executed • The program counter is incremented to
read the next instruction
Processor Speed• Processors (CPUs) have
a clock• Clock speed is measured
in megahertz (MHz) or gigahertz (GHz)
• Some instructions take just 2-3 clock cycles, some take more
• When the clock speed increases the computer can execute instructions faster
Memory• Computer memory is
used to store data • The smallest unit of
memory is a bit (Binary digIT)
• A bit can be off (no voltage) or on (has voltage) which we interpret to be 0 or 1
• Memory is organized into 8 bit contiguous groups called bytes. A megabyte is 1 million bytes. A gigabyte is 1 billion bytes.
Types of Memory• Registers
– Very high speed temporary storage areas for use in the CPU– Used for calculations and comparisons
• Cache– High speed temporary storage for use with the CPU
• Main Memory – Random-access Memory (RAM)– High speed temporary storage – Contains programs and data currently being used– Often described in Megabytes (MB)
• Secondary Memory - Disks– Contains programs and data not currently being used– Often described in Gigabytes (GB)
Why are there so many types of memory?
• The faster memory is the more it costs– So we reduce the cost by using small
amounts of expensive memory (registers, cache, and RAM) and large amounts of cheaper memory (disks)
• Why do we need cache?– Processors are very fast and need quick
access to lots of data– Cache provides quick access to data from
RAM
How does Memory Represent Values?
• The different patterns of the on and off bits in a byte determine the value stored
• Numbers are stored using binary numbers– 101 is 1 * 20 + 0 * 21 + 1 * 22 = 1 + 4 = 5– 1010 is 0 * 20 + 1 * 21 + 0 * 22 + 1 * 23 = 2 + 8 = 10
• Characters are internally represented as numbers– Different numbers represent different characters– There are several systems for assigning numbers to
characters: • ASCII, EBCDIC, and Unicode
Binary Exercise
• Count as high as you can using just the fingers on one hand– You have to count up by ones
• No counting by 10s
– The fingers can be up or down • No in-between states
• How high can you count?
Binary Numbers
• We usually work with decimal numbers with digits from 0 to 9 and powers of 10
7313 = (7 * 1000 + 3 * 100 + 1 * 10 + 3 * 1)
Or (7 * 103 + 3 * 102 + 1 * 101 + 3 * 100)• The binary number system uses digits 0
and 1 and powers of 20101 = (0 * 8 + 1 * 4 + 0 * 2 + 1 * 1)
Or (0 * 23 + 1 * 22 + 0 * 21 + 1 *20)
= 5
Binary Addition• To add two decimal numbers you add the digits and if the
total is greater than ten you carry the one into the next column
• To add two binary numbers – 0 + 0 = 0– 0 + 1 and 1 + 0 = 1– 1 + 1 = 0 with a carry of 1 into the next column to the left
00 10 111
01 01 001
---- --- ------
01 11 1000
00111001010
01010101101
-------------------
10001110111
It’s Hard to Work in Binary
• Convert to Octal– Base 8
– For example:– A is 65 in decimal and
0101 in octal
– What is q in octal?
0161
• Or Hexidecimal– Base 16
– For example:– A is 65 in decimal and
0x41 in hexidecimal
– What is a space in hex?
0x20
Decimal Number Storage
• How do you think a computer stores: 3205.406?– It uses an IEEE 754 format – Converts the number into a value between 0
and 1 raised to a power of 2– Stores 3 things
• A bit for the sign• A number between 0 and 1 (the mantissa)• The power of 2 (the exponent)
Encode and Decode Exercise
• Use Unicode to write a secret message in decimal and then exchange it with another person– See Appendix B in the Java Concepts
textbook for the decimal values for characters
Encodings Make Computer Powerful
• Voltages are interpreted as numbers• Numbers can be interpreted as characters• Characters can be interpreted to be part of
a link to Sun’s Java Site (for example)
0100 0001
off on off off off off off on
a
<a href=http://java.sun.com>Sun’s Java Site </a>
Summary – Part 2• Computers are commonplace and very
important to modern life• Computers are made up of parts
– CPU – calculation and comparisons– Memory – temp storage– Disk – permanent storage– Monitor – Display – Keyboard and mouse – User input
• All data in a computer is stored in bits– More data takes more bits– All characters can be represented as a series of 0s and 1s
Introduction to Java, and DrJavapart 3
Part 3
Introduction to Java, and DrJava
What is DrJava?• DrJava is a free
integrated development environment for doing Java programming– From Rice University– It is written in Java
• It has several window panes in it– For creating programs
(definitions pane)– For trying out Java code
(interactions pane)– Listing of open files (files
pane)
Dr. Java
• We will use Dr. Java to create our Java programs
• But, first, we will use it to try out some mathematical operations
Math Operators in Java (+ * / - %)• Addition
3 + 4• Multiplication
3 * 4• Division
3 / 4 • Subtraction
3 – 4 • Negation
-4• Modulo (Remainder)
10 % 2 and 11 % 2
Math Operators Exercise
• Open DrJava and do the following in the interactions pane– Subtract 7 from 9– Add 7 to 3– Divide 3 by 2– Divide 4.6 by 2– Multiply 5 by 10– Find the remainder
when you divide 10 by 3
Why is the result of 3 / 2 = 1?• Java is a strongly typed language
– Each value has a type associated with it– Tells the computer how to interpret the number
• It is an integer, floating point, letter, etc
• The compiler determines the type if it isn’t specified (literals)– 3 is an integer– 3.0 is a floating point number (has a fractional part)
• The result of an operation is in the same type as the operands– 3 and 2 are integers so the answer is an integer 1
Casting• There are other ways to solve the problem of 3 /
2 has a result of 1• You can make one of the values floating point by
adding .0– 3.0 / 2– 3 / 2.0
• The result type will then be floating point• Or you can cast one of the values to the
primitive types: float or double– (double) 3 / 2– 3 / (float) 2
Casting Exercise
• Use casting to get the values right for splitting up a bill for 3 people of 19 dollars.
• Try it first by hand• Try it in DrJava without casting • Try it in DrJava with casting
Java Primitive Types– Integers (numbers without fractional parts) are
represented by• The types: int or short or long• 235, -2, 33992093, etc
– Floating point numbers (numbers with fractional parts) are represented by• The types: double or float• 3.233038983 -423.9, etc
– A single character is represented by • The type: char• ‘a’ ‘b’ ‘A’ etc
– True and false values are represented by• The type: boolean• true or false
Why so Many Different Types?
• They take up different amounts of space• They have different precisions• Usually use int, double, and boolean
– byte uses 8 bits (1 byte) 2’s compliment– short uses 16 bits (2 bytes) 2’s compliment– int uses 32 bits (4 bytes) 2’s compliment– long uses 64 bits (8 bytes) 2’s compliment– float uses 32 bits (4 bytes) IEEE 754– double uses 64 bits (8 bytes) IEEE 754– char uses 16 bits (2 bytes) Unicode format
Sizes of Primitive Types
byte 8 bits
short
int
float
long
8 bits 8 bits
8 bits 8 bits 8 bits 8 bits
8 bits 8 bits 8 bits 8 bits
8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits
double 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits
char 8 bits 8 bits
Types Exercise
• Which type(s) take up the most space?• Which type(s) take up the least space?• What type would you use for
– The number of people in your family– A grade– The price of an item– The answer to do you have insurance– The number of people in the class– The number of people in your school– The number of people in your state
Floating Point Numbers
• Numbers with a fractional part– 6170.20389
• Stored as binary numbers in scientific notation -52.202 is -5.2202 x 101
– The sign (1 bit)– The digits in the number (mantissa)– The exponent (8 bits)
• Two types– float – 6-7 significant digits accuracy– double – 14-15 significant digits accuracy
Comparison (Relational) Operators• Greater than >
– 4 > 3 is true– 3 > 3 is false– 3 > 4 is false
• Less than < – 2 < 3 is true – 3 < 2 is false
• Equal ==– 3 == 3 is true– 3 == 4 is false
• Not equal !=– 3 != 4 is true– 3 != 3 is false
• Greater than or equal >=– 3 >= 4 is true– 3 >= 3 is true– 2 >= 4 is false
• Less than or equal <=– 2 <= 3 is true– 2 <= 2 is true– 4 <= 2 is false
Comparison Operators Exercise
• In DrJava– Try out the comparison operators in the
interactions pane• with numbers
3 < 44 <= 45 < 46 == 6.0
• with characters (single alphabet letter)Put single quote around a character‘a’ < ‘b’‘b’ < ‘a’‘a’ == ‘a’
Operator Order
• The default evaluation order is – Negation -– Multiplication *– Division /– Modulo (remainder) %– Addition +– Subtraction -
• The default order can be changed– By using parenthesis– (3 + 4) * 2 versus 3 + 4 * 2
Math Operator Order Exercise – Dr. Java
• Try 2 + 3 * 4 + 5• Add parentheses to make it clear what is
happening first• How do you change it so that 2 + 3
happens first?• How do you change it so that it multiplies
the result of 2 + 3 and the result of 4 + 5?
Summary – Part 3• Computers
– Can do math– Can execute billions of instructions per second– Keep getting faster, smaller, and cheaper
• Java has typical math and relational operators• Java is a strongly typed language
– This can lead to odd results • integer division gives a integer result
– You can use casting to solve this• Java has primitive types to represent integer and floating
point numbers• Math operations have a default order
– You can specify the order with parentheses
Georgia Institute of Technology
Hello World!! Our first Java program
public class FirstProgram
{
public static void main( String[] args)
{
System.out.println(“ Hello World !!”);
}
}