Java for Interfaces and Networks (DT3010, HT10)

Transcription

1 Java for Interfaces and Networks (DT3010, HT10) More on Garbage Collection, More on Swing Federico Pecora School of Science and Technology Örebro University Federico Pecora Java for Interfaces and Networks Lecture 9 1 / 21

2 Outline 1 More on Garbage Collection 2 Introspection 3 More on Swing Federico Pecora Java for Interfaces and Networks Lecture 9 2 / 21

3 More on Garbage Collection Outline 1 More on Garbage Collection 2 Introspection 3 More on Swing Federico Pecora Java for Interfaces and Networks Lecture 9 3 / 21

4 More on Garbage Collection Garbage collection in Java When does garbage collection occur? If I instantiate objects with new how do I delete them? Should I trust the garbage collector to do all the work for me?... most of the time :-) Federico Pecora Java for Interfaces and Networks Lecture 9 4 / 21

5 More on Garbage Collection Garbage collection in Java Java garbage collection eliminates the need to free objects explicitly This eliminates a common cause of errors (memory leaks) You never have to worry about dangling references When an object is no longer reachable the space it occupies can be reclaimed Space is reclaimed at the garbage collector s discretion sometimes the programmer should, however, influence what happens when an object is reclaimed typically, when non-java resources are involved Federico Pecora Java for Interfaces and Networks Lecture 9 5 / 21

6 More on Garbage Collection Garbage collection and files FileCounter1.java 1 public class FileCounter1 { 2 public static void main(string[] args) { 3 try { 4 int nrfiles = 0; 5 ArrayList<BufferedReader> files = 6 new ArrayList<BufferedReader>(); 7 while (true) { 8 BufferedReader in = 9 new BufferedReader(new FileReader("dummy.txt")); 10 files.add(in); 11 ++nrfiles; 12 System.out.println("nrFiles = " + nrfiles); 13 } 14 } 15 catch (FileNotFoundException e) { 16 System.out.println("Exception: " + e.getmessage()); 17 } 18 } //main 19 } //class FileCounter1 Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

7 More on Garbage Collection Garbage collection and files linux> java FileCounter1 nrfiles = 1 nrfiles = 2 nrfiles = 3 nrfiles = 4... nrfiles = 1018 nrfiles = 1019 nrfiles = 1020 nrfiles = 1021 Exception: dummy.txt (Too many open files) Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

8 More on Garbage Collection Garbage collection and files (OK, the program is stupid... ) Unsurprisingly, the program crashes All instances of BufferedReader in are accumulated in a list Since all these references stay valid, they are clearly never collected Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

9 More on Garbage Collection Garbage collection and files FileCounter2.java 1 public class FileCounter2 { 2 public static void main(string[] args) { 3 try { 4 int nrfiles = 0; 5 //ArrayList<BufferedReader> files = 6 // new ArrayList<BufferedReader>(); 7 while (true) { 8 BufferedReader in = 9 new BufferedReader(new FileReader("dummy.txt")); 10 //files.add(in); 11 ++nrfiles; 12 System.out.println("nrFiles = " + nrfiles); 13 } 14 } 15 catch (FileNotFoundException e) { 16 System.out.println("Exception: " + e.getmessage()); 17 } 18 } //main 19 } //class FileCounter2 Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

10 More on Garbage Collection Garbage collection and files linux> java FileCounter2 nrfiles = 1 nrfiles = 2 nrfiles = 3 nrfiles = 4... nrfiles = 4951 nrfiles = 4952 nrfiles = 4953 nrfiles = 4954 Exception: dummy.txt (Too many open files) Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

11 More on Garbage Collection Garbage collection and files Again, the program crashes! What is happening? the garbage collector closes files and reclaims memory when it starts running out (see implementation of BufferedReader) BufferedReader.java (probably!) 1 public void close() { 2 if (file!= null) { 3 file.close(); 4 file = null; 5 } 6 } 7 protected void finalize() throws Throwable { 8 try { close(); } 9 finally { super.finalize(); } 10 } Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

12 More on Garbage Collection Garbage collection and files Again, the program crashes! What is happening? the garbage collector closes files and reclaims memory when it starts running out (see implementation of BufferedReader) however, the rate at which files are being opened can lead to a resource limit the OS reaches the soft limit of file descriptors it is willing to give our process In fact, we could get lucky on machines with less memory, the garbage collector may intervene before this limit is reached Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

13 More on Garbage Collection Garbage collection and files linux> java FileCounter2 nrfiles = 1 nrfiles = 2 nrfiles = 3 nrfiles = 4... nrfiles = nrfiles = nrfiles = nrfiles = Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

14 More on Garbage Collection Garbage collection and files Garbage collection occurs at its own pace, in its own thread Cannot count on finalize() method of BufferedReader to close files i.e., BufferedReader s finalize() method closes the file just in case it wasn t i.e., the file certainly has no reason to be open when it is being collected Solution to our problem close the files when not needed! files are non-java resources! Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

15 More on Garbage Collection Garbage collection and files MyFileObject.java 1 class MyFileObject { 2 private final BufferedReader reader; 3 static int nrinstances = 0; 4 public MyFileObject(BufferedReader reader) { 5 this.reader = reader; 6 ++nrinstances; 7 System.out.println("nrInstances up, now " 8 + nrinstances); 9 } 10 public void finalize() { 11 --nrinstances; 12 System.out.println("nrInstances down, now " 13 + nrinstances); 14 } 15 public void close() throws IOException { 16 reader.close(); 17 } 18 } //class MyFileObject Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

16 More on Garbage Collection Garbage collection and files FileCounter3.java 1 public class FileCounter3 { 2 public static void main(string[] args) { 3 try { 4 int nrfiles = 0; 5 while (true) { 6 BufferedReader in = 7 new BufferedReader(new FileReader("dummy.txt")); 8 MyFileObject mfo = new MyFileObject(in); 9 System.out.println("nrFiles = " + (++nrfiles)); 10 mfo.close(); 11 } 12 } 13 catch (FileNotFoundException e) {... } 14 catch (IOException e) {... } 15 } //main 16 } //class FileCounter3 Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

17 More on Garbage Collection Garbage collection and files In summary when garbage collection occurs is out of our control we can only affect what happens when it occurs this is useful for disposing of non-java resources however, non-java resources ned to be disposed of manually as soon as logically possible this includes removing all references (e.g., from containers) this includes performing system-level operations (e.g., closing files) Federico Pecora Java for Interfaces and Networks Lecture 9 6 / 21

18 More on Garbage Collection Garbage collection and JFrames As with files, also JFrames deal with non-java resources... the user! The JVN cannot know when a JFrame ceases to be relevant (except for trivial cases) Also, it is up to the programmer to implement behavior of the JFrame when it closes the default is: do nothing! Problem can arise when an application can spawn new JFrames (e.g., setting options, etc.) Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

19 More on Garbage Collection Garbage collection and JFrames Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

20 More on Garbage Collection Garbage collection and JFrames JFrameExample.java 1 public class JFrameExample { 2 public static int nrchildren = 0; 3 public static void main(string[] args) { 4 JFrame f = new JFrame("This is a test"); 5 f.setsize(200, 150); 6 f.getcontentpane().setbackground(color.white); 7 f.getcontentpane().setlayout(new FlowLayout()); 8 JButton button = new JButton("New frame"); 9 f.getcontentpane().add(button); 10 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

21 More on Garbage Collection Garbage collection and JFrames JFrameExample.java (cont.) 11 button.addactionlistener(new ActionListener(){ 12 public void actionperformed(actionevent arg0) { 13 JFrame childf = new JFrame("Child frame") { 14 protected void finalize() { 15 System.out.println("DOWN: " + --nrchildren); 16 } 17 }; 18 childf.setsize(200, 100); 19 JLabel label = new JLabel("" + 20 new Random().nextDouble()); 21 childf.getcontentpane().add(label); 22 childf.setvisible(true); 23 System.out.println("UP: " + (++nrchildren)); 24 } 25 }); //addactionlistener 26 f.setvisible(true); 27 } //main 28 } //JFrameExample class Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

22 More on Garbage Collection Garbage collection and JFrames linux> java -verbose:gc -Xmx1K JFrameExample [GC 768K->302K(4992K), secs] [GC 1070K->522K(4992K), secs] [GC 1279K->791K(4992K), secs] [GC 1389K->928K(4992K), secs] UP: 1 UP: 2 [GC 1696K->1229K(4992K), secs] UP: 3... UP: 62 UP: 63 [GC 2142K->1786K(4800K), secs] UP: 64 Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

23 More on Garbage Collection Garbage collection and JFrames nrchildren never goes DOWN because JFrames are never collected even if closed the GC lines in the output are the JVM trying to free up space by removing collecting other objects we know it never collects the child JFrames because it never prints DOWN:... This is because the default behavior of JFrame is to make the frame invisible equivalent to setvisible(false) Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

24 More on Garbage Collection Garbage collection and JFrames Overriding default behavior with WindowClosing events JFrameExample.java (part) 1 //What happens when the user closes the JFrame 2 WindowListener windowlistener = new WindowAdapter() { 3 //Anonymous WindowAdapter class 4 public void windowclosing(windowevent w) { 5 //What to do on close, e.g., remember location, 6 //then how to actually close the JFrame, e.g., 7 childf.setvisible(false); 8 childf.dispose(); 9 } //windowclosing 10 }; //anonymous class 11 childf.setdefaultcloseoperation(jframe.do_nothing_on_close); 12 childf.addwindowlistener(windowlistener); Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

25 More on Garbage Collection Garbage collection and JFrames Overriding default behavior with WindowClosing events... or, use one of four shortcuts to writing WindowEvent event handlers JFrameExample.java (part) 1 //This calls dispose() 2 childf.setdefaultcloseoperation (JFrame.DISPOSE_ON_CLOSE); 3 4 //This calls setvisible(false) -- default! 5 childf.setdefaultcloseoperation (JFrame.HIDE_ON_CLOSE); 6 7 //This calls System.exit(0) 8 childf.setdefaultcloseoperation (JFrame.EXIT_ON_CLOSE); 9 10 //This does nothing 11 childf.setdefaultcloseoperation (JFrame.DO_NOTHING_ON_CLOSE); Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

26 More on Garbage Collection Garbage collection and JFrames JFrameExample.java (cont.) 11 button.addactionlistener(new ActionListener(){ 12 public void actionperformed(actionevent arg0) { 13 JFrame childf = new JFrame("Child frame") {... }; 14 childf.setsize(200, 100); 15 JLabel label = new JLabel("" + 16 new Random().nextDouble()); 17 childf.getcontentpane().add(label); 18 childf.setvisible(true); 19 System.out.println("UP: " + (++nrchildren)); 20 childf. 21 setdefaultcloseoperation(jframe.dispose_on_close); 22 } 23 }); //addactionlistener 24 f.setvisible(true); 25 } //main 26 } //JFrameExample class Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

27 More on Garbage Collection Garbage collection and JFrames linux> java -verbose:gc -Xmx1K JFrameExample [GC 768K->306K(4992K), secs] [GC 1074K->526K(4992K), secs] [GC 1283K->788K(4992K), secs] [GC 1381K->930K(4992K), secs] UP: 1 UP: 2 [GC 1698K->1228K(4992K), secs] UP: 3... UP: 20 UP: 21 [GC 1804K->1408K(4800K), secs] DOWN: 20 DOWN: 19 DOWN: 18 DOWN: 17 UP: 18 Federico Pecora Java for Interfaces and Networks Lecture 9 7 / 21

28 Introspection Outline 1 More on Garbage Collection 2 Introspection 3 More on Swing Federico Pecora Java for Interfaces and Networks Lecture 9 8 / 21

29 Introspection What is introspection? Introspection: a way for Java programs to look inside themselves Introspection allows programs to get and use information on classes and objects at run-time Using introspection, one can ask an object for its class ask a class for its methods and constructors find out the details of those methods and constructors tell those methods to execute Federico Pecora Java for Interfaces and Networks Lecture 9 9 / 21

30 Introspection Introspection: the java.lang.class class At the center of Java introspection is the class java.lang.class There are two common ways to obtain a Class object the Object.getClass() method the static Class.forName(String name) method Given a Class type object, you can obtain information on the class name, its fields, its constructors, its methods, and its package getconstructors() returns an array of Constructors getmethods() returns an array of Methods getfields() returns an array of Fields... see Java Class API Federico Pecora Java for Interfaces and Networks Lecture 9 10 / 21

31 Introspection Introspection: the Constructor class A Constructor provides information about, and access to, a single constructor The central method of Constructor is newinstance(object[] initargs) allows to instantiate a new object of that class using a particular constructor returns a new Object instance Federico Pecora Java for Interfaces and Networks Lecture 9 11 / 21

32 Introspection Introspection: the Method class A Method provides information about, and access to, a single method The method can be a class method or an instance method The central method of Method is invoke(object obj, String[] params) allows to invoke the method on a given obj with specific params returns the method s returned Object Federico Pecora Java for Interfaces and Networks Lecture 9 12 / 21

33 Introspection Introspection: obfuscated code example Rewriting the method call foo.bar("baz", 42); with introspection: Code snippet 1 foo.getclass().getmethod("bar",new Class[] { 2 Class.forName("java.lang.String"), 3 Integer.TYPE 4 }). 5 invoke(foo, new Object[] {"Baz", new Integer(42)}); Plug-in support: main application examines each of its plug-ins for the methods it supports and then call them when appropriate Introspection is central to JavaBeans technology We could write an alternative JavaDoc with introspection Federico Pecora Java for Interfaces and Networks Lecture 9 13 / 21

34 Introspection Introspection: simple example IntrospectionTest.java 1 public class IntrospectionTest extends JFrame { 2 public static void showclassinfo(object o) { 3 Class c = o.getclass(); 4 System.out.println("Class: " + c.getname()); 5 Class sc = c.getsuperclass(); 6 System.out.println("Superclass: " + sc.getname()); 7 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 14 / 21

35 Introspection Introspection: simple example IntrospectionTest.java (cont.) 8 Method[] methods = c.getdeclaredmethods(); 9 System.out.println("Methods:"); 10 for (int i = 0; i < methods.length; ++i) 11 System.out.println(" " + methods[i].getname()); 12 Constructor[] constructors = 13 c.getdeclaredconstructors(); 14 System.out.println("Constructors:"); 15 for (int i = 0; i < constructors.length; ++i) 16 System.out.println(" " + 17 constructors[i].getname()); 18 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 14 / 21

36 Introspection Introspection: simple example IntrospectionTest.java (cont.) 19 Field[] fields = c.getdeclaredfields(); 20 System.out.println("Fields:"); 21 for (int i = 0; i < fields.length; ++i) 22 System.out.println(" " + 23 fields[i].getname()); 24 } 25 public static void main(string[] args) { 26 JButton button = new JButton("Hello"); 27 showclassinfo(button); 28 } 29 } //class IntrospectionTest Federico Pecora Java for Interfaces and Networks Lecture 9 14 / 21

37 Introspection Introspection: simple example linux> java IntrospectionTest Class: javax.swing.jbutton Superclass: javax.swing.abstractbutton Methods: writeobject getaccessiblecontext paramstring removenotify getuiclassid isdefaultbutton isdefaultcapable setdefaultcapable updateui Constructors: javax.swing.jbutton javax.swing.jbutton javax.swing.jbutton javax.swing.jbutton javax.swing.jbutton Fields: uiclassid... stay tuned for a more compelling use of introspection in a few slides! Federico Pecora Java for Interfaces and Networks Lecture 9 14 / 21

38 More on Swing Outline 1 More on Garbage Collection 2 Introspection 3 More on Swing Federico Pecora Java for Interfaces and Networks Lecture 9 15 / 21

39 More on Swing A Swing-component example: ButtonGroup ButtonGroup: used to create a multiple-exclusion scope for a set of buttons turning "on" one of those buttons turns off all other buttons in the group Can be used with any set of objects that inherit from AbstractButton JRadioButton, JRadioButtonMenuItem, or JToggleButton,... Federico Pecora Java for Interfaces and Networks Lecture 9 16 / 21

40 More on Swing A Swing-component example: ButtonGroup ButtonGroupTest.java 1 public class ButtonGroupTest extends JFrame { 2 public ButtonGroupTest() { 3 super("buttongrouptest"); 4 Container cp = getcontentpane(); 5 cp.setlayout(new FlowLayout()); 6 ButtonGroup group = new ButtonGroup(); 7 JPanel panel = new JPanel(); 8 panel.setborder(new TitledBorder("3 x JRadioButton")); 9 JRadioButton button1 = new JRadioButton("Tripp"); 10 group.add(button1); 11 panel.add(button1); 12 JRadioButton button2 = new JRadioButton("Trapp"); 13 group.add(button2); 14 panel.add(button2); 15 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 16 / 21

41 More on Swing A Swing-component example: ButtonGroup ButtonGroupTest.java (cont.) 16 JRadioButton button3 = new JRadioButton("Trull"); 17 group.add(button3); 18 panel.add(button3); 19 cp.add(panel); 20 } 21 public static void main(string[] args) { 22 ButtonGroupTest frame = new ButtonGroupTest(); 23 frame.setdefaultcloseoperation(jframe.exit_on_close); 24 frame.setsize(300, 100); 25 frame.setvisible(true); 26 } 27 } //class ButtonGroupTest 28 Federico Pecora Java for Interfaces and Networks Lecture 9 16 / 21

42 More on Swing A Swing-component example: multiple ButtonGroups Now let s use other button types to make multiple button groups... Federico Pecora Java for Interfaces and Networks Lecture 9 17 / 21

43 More on Swing A Swing-component example: multiple ButtonGroups ButtonGroups1.java 1 public class ButtonGroups1 extends JFrame { 2 private static String[] ids = 3 { "Tripp", "Trapp", "Trull" }; 4 public ButtonGroups1() { 5 super("buttongroups"); 6 Container cp = getcontentpane(); 7 cp.setlayout(new FlowLayout()); 8 ButtonGroup group = new ButtonGroup(); 9 JPanel panel = new JPanel(); 10 panel.setborder(new TitledBorder("3 x JButton")); 11 for (int i = 0; i < ids.length; i++) { 12 JButton button = new JButton(ids[i]); 13 group.add(button); 14 panel.add(button); 15 } 16 cp.add(panel); 17 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 17 / 21

44 More on Swing A Swing-component example: multiple ButtonGroups ButtonGroups1.java (cont.) 18 group = new ButtonGroup(); 19 panel = new JPanel(); 20 panel.setborder(new TitledBorder("3 x JToggleButton")); 21 for (int i = 0; i < ids.length; i++) { 22 JToggleButton button = new JToggleButton(ids[i]); 23 group.add(button); 24 panel.add(button); 25 } 26 cp.add(panel); 27 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 17 / 21

45 More on Swing A Swing-component example: multiple ButtonGroups ButtonGroups1.java (cont.) 28 group = new ButtonGroup(); 29 panel = new JPanel(); 30 panel.setborder(new TitledBorder("3 x JCheckBox")); 31 for (int i = 0; i < ids.length; i++) { 32 JCheckBox button = new JCheckBox(ids[i]); 33 group.add(button); 34 panel.add(button); 35 } 36 cp.add(panel); 37 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 17 / 21

46 More on Swing A Swing-component example: multiple ButtonGroups ButtonGroups1.java (cont.) 38 group = new ButtonGroup(); 39 panel = new JPanel(); 40 panel.setborder(new TitledBorder("3 x JRadioButton")); 41 for (int i = 0; i < ids.length; i++) { 42 JRadioButton button = new JRadioButton(ids[i]); 43 group.add(button); 44 panel.add(button); 45 } 46 cp.add(panel); 47 } 48 public static void main(string[] args) { 49 ButtonGroups1 frame = new ButtonGroups1(); 50 frame.setdefaultcloseoperation(jframe.exit_on_close); 51 frame.setsize(300, 300); 52 frame.setvisible(true); 53 } 54 } //class ButtonGroups1 Federico Pecora Java for Interfaces and Networks Lecture 9 17 / 21

47 More on Swing Multiple ButtonGroups and introspection Notice how in the previous example we are repeating similar code four times in the instantiation and addition of buttons to the ButtonGroups Idea: use introspection so we can use more general code... after all, they are all extensions of AbstractButton Federico Pecora Java for Interfaces and Networks Lecture 9 18 / 21

48 More on Swing Multiple ButtonGroups and introspection ButtonGroups2.java 1 public class ButtonGroups2 extends JFrame { 2 private static String[] ids = { "Tripp", "Trapp", "Trull" }; 3 private JPanel makebuttonpanel(class class, String[] ids) { 4 ButtonGroup group = new ButtonGroup(); 5 JPanel panel = new JPanel(); 6 String title = class.getname(); 7 panel.setborder(new TitledBorder(title)); 8 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 18 / 21

49 More on Swing Multiple ButtonGroups and introspection ButtonGroups2.java (cont.) 9 for (int i = 0; i < ids.length; i++) { 10 AbstractButton button = new JButton("failed"); 11 try { 12 Constructor ctor = 13 class.getconstructor(new Class[] {String.class}); 14 button = (AbstractButton) 15 ctor.newinstance(new Object[] {ids[i]}); 16 } 17 catch (Exception e) {... } 18 group.add(button); 19 panel.add(button); 20 } 21 return panel; 22 } //makebuttonpanel method 23 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 18 / 21

50 More on Swing Multiple ButtonGroups and introspection ButtonGroups2.java (cont.) 24 public ButtonGroups2() { 25 super("buttongroups2"); 26 Container cp = getcontentpane(); 27 cp.setlayout(new FlowLayout()); 28 cp.add(makebuttonpanel(jbutton.class, ids)); 29 cp.add(makebuttonpanel(jtogglebutton.class, ids)); 30 cp.add(makebuttonpanel(jcheckbox.class, ids)); 31 cp.add(makebuttonpanel(jradiobutton.class, ids)); 32 } 33 public static void main(string[] args) { 34 ButtonGroups2 frame = new ButtonGroups2(); 35 frame.setdefaultcloseoperation(jframe.exit_on_close); 36 frame.setsize(300, 300); 37 frame.setvisible(true); 38 } 39 } //class ButtonGroups2 Federico Pecora Java for Interfaces and Networks Lecture 9 18 / 21

51 More on Swing Look and Feel The Java Look and Feel (L&F) is the default interface for Java applications Java (L&F) designed for cross-platform use and can provide consistency in the appearance and behavior of common design elements compatibility with industry-standard components and interaction styles aesthetic appeal that does not distract from application content Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

52 More on Swing Look and Feel Default vs. System L&F Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

53 More on Swing Look and Feel Sqrt1.java 1 public class Sqrt1 extends JFrame { 2 private JLabel label = new JLabel("Result"); 3 private JTextField text = new JTextField("Input number"); 4 private JButton button = new JButton("Calculate!"); 5 private ButtonListener bl = new ButtonListener(); 6 public Sqrt1() { 7 super("sqrt1"); 8 button.addactionlistener(bl); 9 Container cp = getcontentpane(); 10 cp.setlayout(new FlowLayout()); 11 cp.add(text); 12 cp.add(button); 13 cp.add(label); 14 } 15 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

54 More on Swing Look and Feel Sqrt1.java (cont.) 16 //member class for button action handling 17 class ButtonListener implements ActionListener { 18 public void actionperformed(actionevent event) { 19 String numbuf = text.gettext(); 20 try { 21 float num = Float.parseFloat(numbuf); 22 float res = (float)math.sqrt(num); 23 if (Float.isNaN(res)) 24 label.settext("number must be positive."); 25 else 26 label.settext("root of " + num + " is " + res); 27 } 28 catch (NumberFormatException exc) { 29 label.settext(" " + numbuf + " is NaN."); 30 } 31 } //actionperformed 32 } //class ButtonListener 33 //continues... Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

55 More on Swing Look and Feel Sqrt1.java (cont.) 34 public static void main(string[] args) { 35 Sqrt1 frame = new Sqrt1(); 36 frame.setdefaultcloseoperation(jframe.exit_on_close); 37 frame.setsize(200, 100); 38 frame.setvisible(true); 39 } Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

56 More on Swing Look and Feel In order to get the system-specific L&F we need specify before instantiating the first JFrame: Sqrt1.java (cont.) 34 public static void main(string[] args) { 35 String laf = UIManager.getSystemLookAndFeelClassName(); 36 try { UIManager.setLookAndFeel(laf); } 37 catch (UnsupportedLookAndFeelException e) { 38 System.err.println("Warning: UnsupportedLnF: " + laf); 39 } 40 catch (Exception e) { 41 System.err.println("Error loading " + laf + ": " + e); 42 } 43 Sqrt1 frame = new Sqrt1(); 44 frame.setdefaultcloseoperation(jframe.exit_on_close); 45 frame.setsize(200, 100); 46 frame.setvisible(true); 47 } Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

57 More on Swing Look and Feel... for the cross-platform L&F: Sqrt1.java (cont.) 34 public static void main(string[] args) { 35 String laf = 36 UIManager.getCrossPlatformLookAndFeelClassName(); 37 try { UIManager.setLookAndFeel(laf); } 38 catch (UnsupportedLookAndFeelException e) { 39 System.err.println("Warning: UnsupportedLnF: " + laf); 40 } 41 catch (Exception e) { 42 System.err.println("Error loading " + laf + ": " + e); 43 } 44 Sqrt1 frame = new Sqrt1(); 45 frame.setdefaultcloseoperation(jframe.exit_on_close); 46 frame.setsize(200, 100); 47 frame.setvisible(true); 48 } Federico Pecora Java for Interfaces and Networks Lecture 9 19 / 21

58 More on Swing Look and Feel on different platforms/jvms See examples in $JAVA_HOME/demo/jfc/SwingSet2/SwingSet2.jar Federico Pecora Java for Interfaces and Networks Lecture 9 20 / 21

59 More on Swing Look and Feel on different platforms/jvms... on linux in 2003 Federico Pecora Java for Interfaces and Networks Lecture 9 20 / 21

60 More on Swing Look and Feel on different platforms/jvms... on windows with system L&F Federico Pecora Java for Interfaces and Networks Lecture 9 20 / 21

61 More on Swing More on Garbage Collection, More on Swing Thank you! Federico Pecora Java for Interfaces and Networks Lecture 9 21 / 21