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CSE 131 Computer Science 1
Module 1: (basics of Java)
Welcome to CSE 131
Professor: Yixin Chen
Head TA: Sam Donohue
URL: http://classes.engineering.wustl.edu/cse131/
Discussion forum:
https://piazza.com/wustl/spring2015/cse131501n/home
All emails: [email protected]
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Logistics
 Structure
of the course
» Lecture, studios, labs, exams
 Feel
free to ask questions
» We move pretty fast (learn it while you are here)
» Getting help: office hours, recitations, tutoring
 Expect
to spend lots of time programming
» Practice makes perfect
 Zero
tolerance on cheating!!
 Reading assignment before each lecture
» It’s for your best interest to finish it
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CS: Automation of processes
 CS
is about automation of computation and processes
 Computers
and computer software are everywhere
» laptops, cell phones, game systems, music players, televisions,
networks, cars, medical devices, appliances
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How Do Computers Work?
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A Little About Computers
very simple
 Memory is storage of data: an array of
numbered storage locations
» each location can store a numeric value
» each location identified by its address
Program
Memory
0
1
2
3
4
...
 Conceptually
Processor
 Processor
is a device that carries out simple machine
instructions
M[2] <=
M[2] <=
if M[3]
M[M[1]]
M[3]
M[3] + M[4] (also, -, *, /,...)
> M[0] then skip ahead 3 (or “go back 5”)
<= M[2] + M[M[4]] (one location “refers” to another)
 Modern
processor can carry out >109 instructions/sec
 So what is programming? – composing instructions to
do a certain task
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Programming Languages
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The Java Programming Language
• Developed by Sun in
1991 for a Green
Project for refrigerators
• The project failed, but
Java thrived
• Today, 1.1 Billion
devices are running
java
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Welcome to the World of Java
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Eclipse
 Integrated
Development Environment (IDE)
» “smart” editing of Java programs – continuous syntax checks
» compiles program files automatically as necessary
» integrated program testing and debugging tools
» has plug-ins for version control system (Subversion)
 Can
be a powerful tool for managing large projects
» but, can also be a bit overwhelming and mysterious at first
» watch the first few Eclipse videos on the web site before lab
 works
the same way in Windows, Mac and Linux
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Your First Program
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, world!");
}
}
» defines a class called HelloWorld (a class defines an object)
» class contains a single method called main
• in Java, the main method is the starting point of a program
• the main method has an array of arguments (not used here)
• Any program has one and only one main() method
» program “prints” a brief message and halts
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Today: understand basic building blocks
of JAVA
 You
will be able to
» Output a slogan on the screen
» Tell if a year is a Leap Year
» Calculate the area of a circle
» Output anything you like
» Do all kinds of calculation
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Basic unit: variable
A
variable in Java is a piece of
information stored in a computer’s
memory: like a jar holding food
 Each variable has a type
» Like different kinds of jars (different
food, size, usage, etc.)
 Main
types:
int a;
double b;
String s;
boolean x;
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Basic Data Types in Java
Type (keyword)
Meaning
Examples
Primitive
Operators
int
Integer
3, 0, -5, 256
+, -, *, /
double
Decimal number
1.5, -3.1415, 0.0
+, -, *, /
boolean
true or false
true, false
&&, ||, !
(return boolean:
<,>,<=,>=,!=,
==)
String
a sequence of
characters
“hello world”
+ (concatenation)
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Basic Definitions
type
Type.
A category of values and a set of operations on such values.
Variable. A name that refers to a value of a declared type.
Assignment statement. Associates a value with a variable.
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The int type
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Integers
This surprises most
students. Don’t feel
bad: experts forget
this too sometimes.
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