Java Coding David Davenport Computer Eng Dept Bilkent

Java Coding. . . David Davenport Computer Eng. Dept. , Bilkent University Ankara - Turkey. email: david@bilkent. edu. tr

IMPORTANT… n Students… This presentation is designed to be used in class as part of a guided discovery sequence. It is not selfexplanatory! Please use it only for revision purposes after having taken the class. Simply flicking through the slides will teach you nothing. You must be actively thinking, doing and questioning to learn! n Instructors… You are free to use this presentation in your classes and to make any modifications to it that you wish. All I ask is an email saying where and when it is/was used. I would also appreciate any suggestions you may have for improving it. thank you, David.

From problem to program… n The story so far. . . Problem Algorithm Data/Memory requirements Java Source Code Java bytecode Machine code

Need Java Syntax for… n Algorithm (in pseudo-code) n n Sequence, Decision & Repetition, of Data flow operations • Input, Output & Assignment n Data/Memory requirements n n Meaningfully named memory locations Restriction on data (data types) Variables or Constants & initial value Plus comments & methods!

Comments & White space n Comments Syntax: n n n Examples: n n n // any text on remainder of current line /* any text across multiple lines */ // Author: David. // Date: Oct. 2002 /* This program blah, blah */ Java ignores line endings, blanks lines & white space! Layout program code for ease of reading!

Identifiers n User-defined names n n n Used for variables, constants, methods, etc. Any sequence of letters, digits and the underscore character only. First character may not be a digit! Upper and lower case are considered different (i. e. case sensitive!) Cannot use Java reserved words • i. e. words such as while, for, class, if, etc. CS 101 rule: Names must be meaningful!

Data Types n Primitive n n n int, long, … (numeric integer) float, double, … (numeric real) char - any character, e. g. A, a, B, b, 3, ? , &, … (Java uses ISO Unicode standard, 16 bit/char) n n boolean - true / false Non-primitive n n n String - any sequence of zero or more characters enum – an ordered set of user-defined values anything & everything else! (we will come to these shortly)

Primitive Numeric Types Type Storage Min Value Max Value byte short int long 8 bits 16 bits 32 bits 64 bits -128 -32, 768 -2, 147, 483, 648 -9 x 1018 127 32, 767 2, 147, 483, 647 9 x 1018 float double 32 bits 64 bits 3. 4 x 10 1. 7 x 10 38 308 7 significant digits 15 significant dig

Data Types n Primitive n n n int, long, … (numeric integer) float, double, … (numeric real) char - any character, e. g. A, a, B, b, 3, ? , &, … (Java uses ISO Unicode standard, 16 bit/char) n n boolean - true / false Non-primitive n n n String - any sequence of zero or more characters enum – an ordered set of user-defined values anything & everything else! (we will come to these shortly)

Declaring Variables n Syntax: n Type n n Any Java type Name (identifier) n n type name; Convention: first letter of embedded words capital, except first! Examples: n n n int age; double area; long initial. Speed; char letter. Grade; char lettergrade; boolean exists; CAUTION Java is case sensitive!

Declaring Constants n Syntax: final type name = value; n Type n n Any Java type Name (identifier) n Convention: all capital letters! n Value (literal, variable, constant, expression) n Examples: n n final int SPEEDOFLIGHT = 300; double TAXRATE = 27. 5; float PI = 3. 142; String COMPANY = “Bilkent”; Literal values String use “…” char use ‘. ’

Output (1) n n Syntax: System. out. println( output ); where output is n Literal value n Named variable or constant Value in named memory location is output n Expression Resulting value of expression is output eg. “The area is “, ‘? ’, 12. 5, … eg. area, user. Name, TAXRATE, … eg. 2 * PI * radius, “The area is “ + area Value is output exactly as is! Note use of + for string concatenation

Output (2) n Use System. out. print( output ); To output the value & leave text cursor on current line. System. out. println( “Welcome to CS 101”); System. out. println( “The tax rate is “ + TAXRATE + ‘%’); System. out. println( “Welcome to CS 101”); System. out. print( “The tax rate is “); System. out. print( TAXRATE); System. out. println( ‘%’); System. out. println(); Output blank line!

Input n Syntax: string. Variable = scan. next(); int. Variable = scan. next. Int(); double. Variable = scan. next. Double(); n Examples Variables must be declared before user. Name = scan. next(); age = scan. next. Int(); salary = scan. next. Double(); str = scan. next. Line(); • Standard from Java 5. 0 on • Invalid input may give run-time error! • Must include: • import java. util. Scanner; • Scanner scan = new Scanner( System. in);

Assignment n Syntax: result. Variable = expression; n where expression is n n operand operator operand & n Operand is • • n Result of expression must be of suitable type to put into result. Variable! Literal value Named Variable or constant Result of method call Expression! Operator is • +, -, *, /, % (modulus, remainder after integer division)

Assignment n Examples sum = first. Number + second. Number; net = gross * ( 1 – TAXRATE/100); count = count + 1; c = Math. sqrt( a * a + b * b ); n What is the value of z? Z = 4 + 2 / 3 – 1; n Evaluation rules n n n Bracketed sub-expressions first Operator precedence ( * & / then + & - ) Left to right

Outline Java Program n The CS 101 console template… Class. Name. java import java. util. Scanner; /** …description… @author …yourname… @version 1. 00, date */ public class Class. Name { public static void main( String[] args) { // constants // variables // program code } } In Java program = class Classname Convention: first letters capitalised Filename & classname MUST be the same.

A Complete Example (1) n n Problem – find area & circumference… Algorithm 1. 2. 3. 4. 5. n Print welcome message Ask for & get radius from user Compute area as pi. radius Compute circumference as 2. pi. radius Report area, circumference & radius Data requirements L radius - int L area, circumference - double PI – double, constant = 3. 142

A Complete Example (2) Area. Circum. java import java. util. Scanner; /** …description… @author …yourname… @version 1. 00, 2005/10/07 */ public class Area. Circum { public static void main( String[] args) { // constants // variables // // // } } 1. 2. 3. 4. 5. Print welcome message Ask for & get radius from user Compute area as pi. radius Compute circumference as 2. pi. radius Report area, circumference & radius

A Complete Example (3) Area. Circum. java import java. util. Scanner; /** * Area. Circum - computes area & circum of circle given radius * * @author David * @version 1. 00, 2005/10/07 */ public class Area. Circum { public static void main( String[] args) { // constants final double PI = 3. 142; // variables int radius; double area; double circumference; Header has been edited to include program description & author name

A Complete Example (3) Scanner scan = new Scanner( System. in); // 1. Print welcome message System. out. println( "Welcome to area circumference finder. "); Added line to get Keyboard input. // 2. Ask for & get radius from user System. out. print( "Please enter the radius: "); radius = scan. next. Int(); // 3. Compute area as pi. radius area = PI * radius; // 4. Compute circumference as 2. pi. radius circumference = 2 * PI * radius; // 5. Report area, circumference & radius System. out. print( "The area of a circle of radius "); System. out. print( radius); System. out. print( " is "); System. out. println( area); System. out. print( "and its circumference is "); System. out. print( circumference); System. out. println(); } } // end of class Area. Circum Steps 2 & 5 expanded as per original algorithm.