1. Java Programming The Language of Now & the Future* Lecture 0 An Introduction to Java Syntax for Non-C Programmers John Morris Department of Electrical and Electronic Engineering, University of Western Australia * The presenters of this course wish to disclaim responsibility this corny part of the title! John Morris Peter Jones

2. Program Object Oriented Design Objects and Classes Inheritance Interfaces Java Programs and Applets Graphical User Interfaces Swing Windows, Frames, Menus,... Practical Session Week 2 Week 1 Week 3

3. Program Object Oriented Design Objects and Classes Inheritance Interfaces Java Programs and Applets Graphical User Interfaces Swing Windows, Frames, Menus,... Practical Session Week 5 Week 4 Week 6

4. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; }

5. Primitive Types Boolean boolean Values true false Not in C!

6. Primitive Types Character char Unicode Uses two bytes Designed for “internationalisation” More later! Literals Single quotes ‘Ordinary’ (printing) characters ‘a’, ‘A’, ‘!’, ‘1’,... Special Hexadecimal form ‘\u0008’ (Unicode backspace)

7. Primitive Types Character char Literals Non-printing characters Use \ as escape character ‘\b’ backspace ‘\t’ tab ‘\n’ linefeed ‘\r’ return ‘\”’ double quote ‘\’’ single quote ‘\\’ backslash itself!

8. Primitive Types Integers Many flavours (just like C ) int 4 bytes short 2 bytes long 8 bytes byte 1 bytes (not in C) (Use in low level file handling char is Unicode!) Literals [ sign ] { decimal digits } : 1, +1, -1, 9999,.... L suffix for long : 123456789122L 0x prefix for hexadecimal: 0x234ab

9. Primitive Types Floating point Two flavours (as C) float 4 bytes double 8 bytes Literals [+|-] { dec digit }.[ { dec digit } ] [e|E] [+|-] { dec digit } 1. 1.0 1.E+6 1.2e-6 -1.3e-06 1.896

10. Primitive Types Arrays Rather different from C! int [] intArray;... intArray = new int[n]; double [] dlist = new double[n]; Initialised arrays int[] primes = { 2, 3, 5, 7, 11 }; Array attributes int n = primes.length; More later!

11. Primitive Types Constants No preprocessor (as C)! Use final keyword static final int n = 100; int [] intArray;... intArray = new int[n]; double [] dlist = new double[n];

12. Class Example - Java code Rectangle.java Block delimited by { } class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } 12

13. Declarations type_name variable_name_list ; boolean ok, finished; char tab, separator; int k, j; byte c, d; float x, y; double a, b; May occur anywhere in a block C: must be at head of block Scope Valid within the block

14. Class Example - Java code Rectangle.java Compilable program unit class one or more classes per file package several classes used for making libraries class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; }

15. Methods (functions) [ public | private ] return_type name ( parameter_list ) block public int count( double a ) { some_statements; } public - accessible outside the class private - accessible inside the class only Some other qualifiers (later!) static, protected, synchronized

16. Methods (functions) [ public | private ] return_type name ( parameter_list ) block public int count( double a ) { some_statements; } return_type - any Java type or class void - method doesn’t return a value but may update an object

17. Methods (functions) [ public | private ] return_type name ( parameter_list ) block public int count( double a ) { some_statements; } name - any legal name must begin with a character letters, numbers, _ Convention setValue, raiseSalary, printTable common, but not mandatory!

18. Methods (functions) [ public | private ] return_type name ( parameter_list ) block public int count( double a ) { some_statements; } parameter_list - comma separated list type name pairs void setPoint( double from, double to ); void update( Graphics g ); void setNewValues( int[] a );

19. Methods (functions) [ public | private ] return_type name ( parameter_list ) block public int count( double a ) { some_statements; } block - delimited by { } contains sequences of declarations & statements ; is terminator not separator (as some languages)

20. Statements Assignment l_value = expression a = b; x = y = 0.0; z = f( x, a ) * g( y, b ); Statements are expressions

21. Expressions Operators = assignment operator +, -, *, / arithmetic operators % modulus (remainder) ! complement > left, right shift &, |, ^ arithmetic and, or, xor, >= relational == relational eq &&, || boolean and, or ++, -- increment, decrement ?: if(x) a else b

22. Expressions Operators > left, right shift a > 2 divide b by 4 x > k y / 2 k

23. Expressions Operators &, |, ^ arithmetic and, or, xor a & b bitwise and of a and b a | b bitwise or x ^ y x xor y Care a && b a & b Both legal, very different meaning!

24. Expressions Operators == relational equal if ( a == b ).. not if ( a = b ) assignment operator!

25. Expressions Operators &&, || boolean and, or if ( (a == b) && (x != y) )... again not if ( (a=b) & (x=y) ).. arithmetic operators!

26. Expressions Operators ++, -- increment, decrement x++ use x, then increment y-- use y, then decrement --x decrement x, then use it ++y increment y, then use it Postfix and prefix operators are quite different!

27. Expressions Operators ?: if(x) a else b (a==b)?x:y if( a== b) x else y (a>b)?a:b max of a and b

28. Statements IF if( exp ) statement1; else statement2; if (a>b) x = a; else x = b; else is optional if ( x[i] > max ) max = x[i];

29. Statements Loops while while( exp ) statement1; while( exp ) { statements; } while (a>b) a = x[i++]; while ( x < 0 ) { x = getX(... ); y = y + x; } while is zero-trip

30. Statements Loops do do statement; while( exp ); do { statements; } while( exp ); do a = x[i++]; while( a>z ); do { x = getX(... ); y = y + x; } while ( x > 0 ); do is one-trip

31. Statements - Loops for for( exp1; exp2; exp3 ) { s; } equivalent to: exp1; while ( exp2 ) { s; exp3; } for( k=0; k<n; k++ ) { s; } k=0; while( k<n ) { s; k++; } Standard pattern for n iterations!

32. Statements - switch switch( exp1 ) { case x1: s1; break; case x2: s2; break; default: s3; } switch( x ) { case 1: y = a; break; case 2: y = b; break; default: y = c; }

33. Strings Standard class Package : java.lang Literals “abcd” “123”

34. Objects for primitive data types Wrappers Make objects from standard data types java.lang Boolean Integer Long Character Float Double

35. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } class Rectangle { private double width, height; // attributes....... } Class name

36. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } class Rectangle { private double width, height; // attributes....... } Class name Block delimiters

37. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } class Rectangle { private double width, height; // attributes....... } Class name Attributes Block delimiters

38. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } class Rectangle { private double width, height; // attributes....... } Class name Attributes Note that in all our examples, we mark the attributes private ! In good designs, classes are black boxes!

39. Class Example - Java code Rectangle.java class Rectangle { private double width, height; // attributes public Rectangle( double w, double h ) { // constructor width = w; // set attributes from height = h; // parameters } double Height( ) { // projector return height; // simply returns value } // of an attribute double Width( ) { return width; } double getArea( ) { // projector return width*height; // returns the value of an attribute } // which it calculates double getPerimeter( ) { return 2.0*(width + height); } void setHeight( double h ) { // update method height = h; // changes the value of an } // attribute void setWidth( double w ) { width = w; } class Rectangle { private double width, height; // attributes....... } Class name Attributes Note that in all our examples, we mark the attributes private ! In good designs, classes are black boxes!