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Georgia Tech - CS 1331 - CS 1331, Week one notes - Class Notes

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Georgia Tech - CS 1331 - CS 1331, Week one notes - Class Notes

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background image 1.1­1.10 01/09 Java made in the early 90s by Sun Microsystems Went public in ‘95 An example program
public class Test {
public static void main (String [] args){ System.out.printIn(“A test program”); } } //A comment
/* A longer
comment */ The file name must match the name of class Programming Language Levels Interpreted language (Python)
Interleave, translation & execution
Compiled Language (C)
High level source code, assembly, machine language
Typically source code  machine language (unique to a hardware type)
For JAVA:
Java Source Java Compiler  Java bytecode  Bytecode compiler
|            v Java Interpreter Java is system neutral Compiler + interpreter is part of the JAVA SE Development Kit (JDK) IDE – Integrated Development Environment v11 JRE – Java Runtime Environment Syntax + Semantics Java: Object Oriented Language
background image Objects have:
i.
State: Characterized by attributes of object ii. Behaviors: Characterized by methods of object Ex: Car Attributes: color, year, miles Methods: Start the car, drive, brake Class: Model or blueprint from which objects are made. Can make multiple objects from it. Encapsulation: Each object is ultimately responsible for managing its own data Inheritance: Classes form a hierarchy (Children classes get all the info of the main class) 2 01/09 public   class   Example  {      public   static   void   main ( String  []  args ){          int   jan ;         jan =  30  +  1          System . out . println ( "Jan has "  + jan +  "days" );     }
}
Identifiers 1. Programmer defined. Examples: args, jan 2. Other programmer defined. Examples: System, String, println
3. Reserved Words. Examples: public, class, void
Variables: Case sensitive locations in memory used to hold a data value In java you have to declare the variable, unlike python. (Example: how we used int to define 
jan)
int total;
double pi = 3.141;
(can have an initial value)(can change these values later) pi = 6.873; (changes the value of pi) total = 17; total = total + 3; Java is a strongly types language: Cannot assign inappropriate values to variables
total = “xyz”;
Cannot do this since it has been assigned int Declaring constants (These are like variables but value can’t be changed):
background image final int months = 12;
(using the word final finalizes the value)
Once you assign the type to a variable, it can’t be changed Primitive Data Types Integers – byte, short, int, long (8, 16, 32, 64) Floating point numbers – float, double (32, 64) 12: Literal value (can’t be changed) integer literal – int
floating point literal – double
To change:
12l
12L 3.3F 3.3f Characters – char
char literal – ‘a’
‘Q’ ‘!’ char gender = ‘m’; (only a single character) Ascii codes – 8 bits of info (2 8 ) 0  255 Java uses the Unicode instead of Ascii – 16 bits of info (2 16 ) 65,536 chars Boolean – boolean
boolean hot;
boolean easy = true;
Expression Combination of one or more operators or operands
+ ­ * / %
­18 % 4
(­2)(You use the sign of the numerator) 18 / 4 = 4 (integer division) 18/4.0 = 4.5 total = 2 + 3 * 5; Precedence rules: Different levels and some ops are stronger
At same level: left  right
Can force parentheses
1. +­ unary ops
works R  L 2. * / % L  R 3. + ­ L  R 4. = R  L Always use PARENS
Some Operators
Increment Operator : ++ (adds 1 to value)
background image Decrement operator : ­­ (subtracts 1 from value) total ++; (total = total +1) ++ total; (total = total + 1) total = 5; sum = total ++; (the value of sum is figured out first) Here, total becomes 6, sum is 5 total = 5; sum = ++ total
Here, it is pre increment and sum becomes 6
sum += 12; equivalent to sum = sum + 12
result /= a+ b * (c­12)
result = result / a+ b * (c­12) 01/11 There are times when we want to change from one type to another short  long (narrowing) /Won’t work long  short (widening) / OK Three ways to do conversions:
1. Assignments
int sum; double avg;
avg = sum;
(int into double is allowed) sum = avg; (double into int is not allowed) 2. Arithmetic promotion double result; result = sum/avg (Allowed. The int is bumped up to be a double) 3. Casting Using parentheses to transform one type to another sum = (int)avg; (Does truncation) int a = 5, b = 2;
double total;
total = (double)a/b
total = 2.5

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School: Georgia Institute of Technology
Department: Computer Science and Engineering
Course: Intro-Object Orient Prog
Professor: John Statsko
Term: Spring 2019
Tags: Java basics
Name: CS 1331, Week one notes
Description: These are the in class notes for the first 3 classes in the first week conducted by John Stasko
Uploaded: 12/30/2018
16 Pages 84 Views 67 Unlocks
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