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Copyright 2009 by Pearson Education
Building Java Programs
Chapter 1Lecture 1-1: Introduction; Basic Java Programs
reading: 1.1 - 1.3self-check: #1-14exercises: #1-4
Copyright 2009 by Pearson Education 2
Today’s lectureIntroduction
Syllabus and policiesWhat is CSE – myths debunked!What is CSE 142
Basic Java programsOutput with println statementsSyntax and errorsString literals and escape sequences
Copyright 2009 by Pearson Education
Introduction
reading: 1.1self-check: #1-4
Copyright 2009 by Pearson Education 4
Syllabus in a nutshellCourse website is super important and useful:
http://cs.washington.edu/142The textbook is STRONGLY recommendedSection attendance is required
Can miss up to 2 sections and still get full creditThere is section this Thursday
Schedule exam makeups BEFORE test5 free ‘late days’ for your homeworksProgramming lab (IPL) where TAs can answer questionsDon’t share code; obey academic integrity policy
Copyright 2009 by Pearson Education 5
CSE majors spend lives in dark offices alone writing code
CSE graduates can’t get jobs anymoreThe dot-com bubble burst, out-sourcing, etc.
The only people who do well in CSE 142 have programmed since they were five
Related: CSE majors all look like this guy ------->
See: http://www.cs.washington.edu/whycse
Myths about CSE
Copyright 2009 by Pearson Education 6
What is CSE?Computer Science
Study of computation (information processing) Automating the organization and analysis of information
Many subfields Graphics, Computer Vision Computational Biology Robotics / Artificial Intelligence Large-scale data processing ...
Writing code is a means to an end
Computer EngineeringOverlap with CS and electrical engineeringEmphasis on hardware-software integration
Copyright 2009 by Pearson Education 7
The CS job market
Computer science Biological science-
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
PhDMaster'sBachelor'sProjected Job Openings
SOURCES: Tabulated by National Science Foundation/Division of Science Resources Statistics; data from Department of Education/National Center for Education Statistics: Integrated Postsecondary Education Data System Completions Survey
Copyright 2009 by Pearson Education 8
What is CSE 142?CSE 142 is an introduction to programming
Creating instructions for computersUses a language (human-readable notation)“CSE” is not just programming, but programming is a good
starting point
No prior programming knowledge assumedShould know how basics of to use a computerShould know math through Algebra IStudents with significant programming experience should not be
here – take CSE 143 instead (no special permission needed)
Copyright 2009 by Pearson Education
Basic Java programs with println statements
reading: 1.2 - 1.3self-check: #5-14exercises: #1-4
Copyright 2009 by Pearson Education 10
Writing a programprogram: a sequence of instructions that a computer can
understand and performA computer is a servant that does precisely what you tell it to do.
Must speak to your computer in a language it understandsWe’re going to talk to our computer in Java
Copyright 2009 by Pearson Education 11
JavaA modern programming language
Sun Microsystems in 1995Rich librariesCross-platformObject-oriented
Taught in 142 and 143Shows basic conceptsGood free, cross-platform toolsIndustry-grade language
Copyright 2009 by Pearson Education 12
Compiling/running a program1. Write it.
code or source code: The set of instructions in a program.
2. Compile it.• compile: Translate a program from one language to another.byte code: The Java compiler converts your code into a format
named byte code that runs on many computer types.
3. Run (execute) it.output: The messages printed to the user by a program.
source code compile
byte code run
output
Copyright 2009 by Pearson Education 13
A Java Programpublic class Hello { public static void main(String[] args) { System.out.println("Hello, world!"); System.out.println(); System.out.println("This program produces"); System.out.println("four lines of output"); }}
Its output:Hello, world!
This program producesfour lines of output
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Structure of a Java programpublic class name { public static void main(String[] args) { statement;; statement;; ...... statement;; }}
Every executable Java program consists of a class,that contains a method named main,
that contains the statements (commands) to be executed.
class: a program
statement: a command to be executed
method: a named groupof statements
Copyright 2009 by Pearson Education 15
System.out.println
A statement that prints a line of output on the console.pronounced "print-linn"sometimes called a "println statement" for short
Two ways to use System.out.println :• System.out.println("text");
Prints the given message as output.
• System.out.println();Prints a blank line of output.
Copyright 2009 by Pearson Education 16
Names and identifiersYou must give your program a name.
public class CakeRecipe {Naming convention: capitalize each word (e.g. MyClassName)Your program's file must match exactly (CakeRecipe.java)
includes capitalization (Java is "case-sensitive")
identifier: A name given to an item in your program.must start with a letter or _ or $subsequent characters can be any of those or a number
legal: _myName GuyBrush ANSWER_IS_42 $bling$
illegal: me+u 49ers side-swipe Ph.D's
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Keywordskeyword: An identifier that you cannot use because it
already has a reserved meaning in Java. abstract default if private this boolean do implements protected throw break double import public throws byte else instanceof return transient case extends int short try catch final interface static void char finally long strictfp volatile class float native super while const for new switch continue goto package synchronized
i.e., You may not use char or while for the name of a class.
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Syntaxsyntax: The set of legal structures and commands that
can be used in a particular language.Every basic Java statement ends with a semicolon ;The contents of a class or method occur between { and }
syntax error (compiler error): A problem in the structure of a program that causes the compiler to fail.Examples:Missing semicolonToo many or too few { } bracesIllegal identifier for class nameClass and file names do not match...
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Syntax error example1 public class Hello {2 pooblic static void main(String[] args) {3 System.owt.println("Hello, world!")_ 4 }5 }
Compiler output: Hello.java:2: <identifier> expected pooblic static void main(String[] args) { ^ Hello.java:3: ';' expected } ^ 2 errors
The compiler shows the line number where it found the error.The error messages can be tough to understand!
Copyright 2009 by Pearson Education 20
Stringsstring: A sequence of characters to be printed.
Starts and ends with a " quote " character.The quotes do not appear in the output.
Examples:
"hello""This is a string. It's very long!"
Restrictions:May not span multiple lines."This is nota legal String."
May not contain a " character."This is not a "legal" String either."
Copyright 2009 by Pearson Education 21
Escape sequencesescape sequence: A special sequence of characters used
to represent certain special characters in a string.
\t tab character\n new line character\" quotation mark character\\ backslash character
Example:System.out.println("\\hello\nhow\tare \"you\"?\\\\");
Output:\hellohow are "you"?\\
Copyright 2009 by Pearson Education 22
QuestionsWhat is the output of the following println
statements?
System.out.println("\ta\tb\tc");System.out.println("\\\\");System.out.println("'");System.out.println("\"\"\"");System.out.println("C:\the beatles\norwegian wood.mp3");
Write a println statement to produce this output:/ \ // \\ /// \\\
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AnswersOutput of each println statement:
a b c\\'"""C: he beatlesorwegian wood.mp3
println statement to produce the line of output:System.out.println("/ \\ // \\\\ /// \\\\\\");
Copyright 2009 by Pearson Education 24
QuestionsWhat println statements will generate this output?
This program prints aquote from the Gettysburg Address.
"Four score and seven years ago,our 'fore fathers' brought forth onthis continent a new nation."
What println statements will generate this output?A "quoted" String is'much' better if you learnthe rules of "escape sequences."
Also, "" represents an empty String.Don't forget: use \" instead of " !'' is not the same as "
Copyright 2009 by Pearson Education 25
Answersprintln statements to generate the output:
System.out.println("This program prints a");System.out.println("quote from the Gettysburg Address.");System.out.println();System.out.println("\"Four score and seven years ago,");System.out.println("our 'fore fathers' brought forth on");System.out.println("this continent a new nation.\"");
println statements to generate the output:System.out.println("A \"quoted\" String is");System.out.println("'much' better if you learn");System.out.println("the rules of \"escape sequences.\"");System.out.println();System.out.println("Also, \"\" represents an empty String.");System.out.println("Don't forget: use \\\" instead of \" !");System.out.println("'' is not the same as \"");
Copyright 2009 by Pearson Education 26
Commentscomment: A note written in the source code by the
programmer to make the code easier to understand.Comments are not executed when your program runs.
Comment, general syntax:// <comment text, on one line>
or,/* <comment text; may span multiple lines> */
Examples:/* A comment goes here. *//* It can even span multiple lines. */// This is a one-line comment.
Copyright 2009 by Pearson Education 27
Comments example/* Patty Println, CS 101, Fall 2019 This program prints lyrics from my favorite song! */public class Washington { // The code to print the song on the console. public static void main(String[] args) { // first verse System.out.println(“Washington, Washington"); System.out.println(“6 foot 8"); System.out.println(“Weighs a friendly ton");
// separate the lyrics with a blank line System.out.println();
// second verse System.out.println(“Opponents beware"); System.out.println(“Opponents beware"); }}