Assignment 2. Naming policy. Stack Trace. Actions Internationalization (I18N) Progress Icons Resize. getlastname() setmaxoflines(int i)

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1 Assignment 2 Actions Internationalization (I18N) Progress Icons Resize #1 getlastname() setmaxoflines(int i) Naming policy String longname = foo ; int loopcounter = 7; #2 Stack Trace java.lang.nullpointerexception at se.uu.it110.icqui.icqclient.setstatus(icq- Client.java:102) at se.uu.it110.icqui.icqui$15.actionperformed(icqui.java:343) at javax.swing.jcombobox.fireactionevent(jcombobox.java:654) at javax.swing.jcombobox.selecteditemchanged(jcombobox.java:678) at javax.swing.jcombobox.contentschanged(jcombobox.java:730) at javax.swing.abstractlistmodel.firecontentschanged(abstractlistmode.ja va:82) at javax.swing.defaultcomboboxmodel.setselecteditem(defaultcombobox Model.java:90) at javax.swing.jcombobox.setselecteditem(jcombobox.java:377) at javax.swing.jcombobox.setselectedindex(jcombobox.java:414) at #3 1

2 Quality result Few lines of code is easier to read, maintain, understand etc. Less code means you see more of the program per page #4 Code style // too much code private JPanel getfilepanel() { JPanel p = new JPanel(); JScrollPane s = new JScrollPane(fileTable); p.add(s); return p; // compact is better private JPanel getfilepanel() { JPanel p = new JPanel(); p.add(new JScrollPane(fileTable)); return p; #5 Compact // method, 1 line public String getcolumnname(int col) { return headers[col]; // construktor FileModel(User user) { this.user = user; // simple test if (test == true) return; // vs. if (test) return; #6 2

3 javax.swing.action Interface, contains Accelerator, Mnemonic, Name, Icon, Description (short+long), Enabled?, command javax.swing.abstractaction default implementations for the Action interface new JButton(new ExitAction()); new JButton(new ExitAction(initValue)); #7 Action example Action playaction = new AbstractAction( Play", new ImageIcon( play.gif")) { public void actionperformed(ae e) { move( left ); ; JButton b = new JButton(playAction); JMenuItem menuitem = commandmenu.add(playaction); playaction.setenabled(false); #8 Action The previous example is not good enough; we also need: mnemonic, description, I18n #9 3

4 I18N See build.xml, target run File: player/ui/lang.properties: ui.ok = Ok ui.cancel = Cancel File: player/ui/lang_sv.properties: ui.ok = Okej ui.cancel = Avbryt ResourceBundle rb = ResourceBundle.getBundle( player.ui.lang ); String okstring = rb.getstring( ui.ok ); JButton okbutton = new JButton(okString); #10 java.util.resourcebundle Be specific and clear! Like this; ui.menu.exit.name ui.menu.exit.mne = Exit = x Not like this: exit=exit #11 Icons URL u = Player1.class.getResource("exit.gif"); JButton exitbutton = new JButton(new ImageIcon(u)); At runtime, exit.gif must be located next to Player1.class Icons also need to be in CVS Location, next to source code Binary files need extra flag cvs add kb binary.gif #12 4

5 Collections Eckel: chapter Collections of Objects Read about containers, skip arrays List stores objects in sequence Set stores unique objects in a space Map manages key/value pairs #13 Iterators Abstraction, you don t care about the storage Iterators are lightweight and do not consume a lot of resources Iterator it = collection.iterator(); while (it.hasnext()) { Object o = it.next(); #14 Iterator, exemple public List getnames(collection col) { Vector names = new Vector(); Iterator it = col.iterator(); while (it.hasnext()) { String name = ((Person)it.next()).getName(); names.add(name); return names; #15 5

6 Map import java.util.*; class Counter { int i = 1; public String tostring() {return Integer.toString(i); class Statistics { public static void main(string[] args) { HashMap ht = new HashMap(); for (int i = 0; i < 10000; i++) { Integer r = new Integer((int)(Math.random() * 20)); if (ht.containskey(r)) ((Counter)ht.get(r)).i++; else ht.put(r, new Counter()); System.out.println(ht); #16 Collections public class Log { private static final int MAX = 1000; private Map map = new HashMap(); private List list = new Vector(); private Set set = new HashSet(); Log() { Random rnd = new Random(); for (int i = 0; i < 10; i++) { map.put(new Integer((int)(System.currentTimeMillis() % MAX)), "foo"); list.add(new Integer(rnd.nextInt(MAX))); set.add(new Integer(rnd.nextInt(MAX))); dump(map.keyset()); dump(list); dump(set); public void dump(collection c) { Iterator iterator = c.iterator(); System.out.println("\n" + "Collection: " + c); while (iterator.hasnext()) { System.out.println("" + iterator.next()); public static void main(string[] argv){ Log l = new Log(); #17 // create a sorted set SortedSet s = new TreeSet(); s.add("string1"); s.add("string2"); s.add("string3"); s.add("string4"); s.add("string5"); // get a subset of the set and display it Set sub = s.subset("a", "ZZZZZZ"); Iterator i = sub.iterator(); while (i.hasnext()) { System.out.println(i.next()); System.out.println(); // remove an element from the original set s.remove("string3"); SortedSet // display the subset again i = sub.iterator(); while (i.hasnext()) { System.out.println(i.next()); #18 6

7 public class Foo { int i; Inner class public class Bar { int k = i; void test() { A a = new A(); B b = new B(); #19 Inner classes, upcasting interface Bills { int getnoof100(); public class ATM { public Bills getbillstatus() { return new S(); // we only have 500! private class S implements Bills { public int getnoof100() { return 0; public int get500() { return 42; #20 Inner classes, anonymous interface Bills { int getnoof100(); public class ATM { public Bills getbillstatus() { return new Bills() { public int getnoof100(){ return 0; ; ; #21 7

8 Is there a difference? interface Bills { int get100(); Bills s1 = new Bills() { public int get100() { return 0; ; class Foo implements Bills { public int get100() { return 0; Bills s2 = new Foo(); #22 Scope for inner class If you re defining an anonymous inner class and want to use an object that s defined outside the anonymous inner class, the compiler requires that the argument reference be final, like the argument to dest( ). If you forget, you ll get a compile-time error message. An inner class can see Outer surrounding class (it s globala attributes) final #23 Scope class Bank { int i; void bills() { int k = 0; final f = 7; Bills s1 = new Bills() { // see i & f, not k public int get100() { return 0; ; #24 8

9 ActionListener (AL) // Not OOP class Foo implements ActionListener { Foo() { JButton b = new JButton(); b.addactionlistener(this); // ugly! public void actionperformed(actionevent e) { // doit #25 AL 2 // Sometimes ok, mostly not class Foo { class Bar implements ActionListener { public void actionperformed(actionevent e) { // doit Foo() { JButton b = new JButton(); b.addactionlistener(new Bar()); #26 AL 2.1 class Foo { class Bar implements ActionListener { public void actionperformed(actionevent e) { // doit Foo() { Bar bar = new Bar(); JButton b1 = new JButton(); JButton b2 = new JButton(); b1.addactionlistener(bar); b2.addactionlistener(bar); // smart, shares action #27 9

10 AL 3 // Good! class Foo { Foo() { JButton b = new JButton(); b.addactionlistener(new ActionListener() { public void actionperformed(actionevent e) { // doit ); #28 AL 4 scope? class Foo { private int i; Foo() { int k = 0; final m = 0; JButton b = new JButton(); b.addactionlistener(new ActionListener() { public void actionperformed(actionevent e) { // can see i and m, not k ); #29 10