1	CS110 Lecture 14 Tuesday, March 23, 2004 Announcements hw6 due Thursday pass/fail, withdraw deadline April 8 Agenda Questions Java 1.5 Inheritance (Chapter 5) Shapes JFile, TextFile and Directory
2	Java version 1.5 Beta release available from Sun download now for your PC if you wish no midsemester change to lab computers Improved collection management Casts no longer required Automatic wrapping of primitive types New for loop syntax replaces Iterator idiom See java 1.5 link on course home page TreeMap15Demo.java available there
3	Backward compatibility Important software design issue Java 1.5 has no new keywords To compile java 1.4 source code with 1.5 javac Whatever.java To compile java 1.5 features javac –source 1.5 Whatever.java java 1.4 code still compiles (but with warnings) What should JOI do?
4	TreeMap (1.5) summary declaration: TreeMap<KeyType, ValueType> mapName; creation: new TreeMap<KeyType, ValueType> ( ); put: mapName.put(KeyType key, ValueType val) get: mapName.get( KeyType key) no cast to ValueType needed length: mapName.size( ) looping: for( KeyType key : mapName.keySet( )) { // do whatever with key }
5	New for syntax works with arrays too zamples.com/JspExplorer/samples/ samplesJDK1_5.html But note how this code violates our conventions we require int[] array braces should surround one line for loop body
6	Design problem Bigbank and Littlebank are similar but different Both have fields name, balance, transaction count (same meaning) accountList (different meanings) Both have methods visit, processTransaction, getBalance, … (same code) whichAccount, report (different code) Can we write big and little Bank classes without copying code?
7	Design problem Directory should store TextFiles and Directories Directory and TextFile both have owner, create/mod date (same meaning) size, contents (different meanings) Directory has methods to add to, get from and loop on its contents (the TreeMap of files in it) TextFile has methods to manipulate its text Can we write these classes without copying code?
8	Design problem HLine and VLine each have length, paintChar, with setters and getters Each kind of line has a paintOn method to paint itself on a Screen in its own particular way When you wrote VLine you started with a copy of HLine, and changed a small fraction of the code Is there a better way? Yes
9	Why do we need a better way? Copy code and change a little bit Þ design problem can’t see similarities and differences bugs must be fixed in two places Inheritance solves this problem Inheritance is the second Big Thing in OOP (sending messages is the first Big Thing)
10	Inheritance
11	How inheritance works (Hline.java main) 64 Line hline = new HLine( 10, ‘x’); Variable hline declared of type Line can have a value that’s a reference to an instance of some child of Line Line foo = new Line() not legal (since Line is abstract) 70 hline.setPaintChar(‘*’); Send setPaintChar message to Line hline, which happens to be an HLine Java looks for setPaintChar method in class Hline Not there! So looks in parent class Line Found it! So search stops
12	How inheritance works 65 hline.paintOn(screen); Send paintOn message to Line hline, which happens to be an HLine No paintOn(Screen) in class HLine Java finds paintOn(Screen) in parent class Line paintOn(Screen) delegates to paintOn(Screen, int, int) paintOn(Screen, int, int) is abstract in class Line Java finds implementation in class HLine
13	abstract New Java keyword abstract class can’t be instantiated (only its children can) abstract method is a signature with no body (just a promise)
14	Constructors in a subclass 64 Line hline = new HLine( 10, ‘x’); invokes HLine constructor 20 public HLine( int length, char paintChar ) 21 { 22 super( length, paintChar ); 23 } line 22: invokes parent class (Line) constructor (java keyword super is “my parent”)
15	Shapes in hw7
16	Trees Common in computer science: Java class hierarchy (shows inheritance) Windows tree for files and directories (folders) Vocabulary: Tree, hierarchy Root (often drawn at the top!) Child, parent, branch, leaf, node Draw with arrows, or in outline (indented) form