Java for Interfaces and Networks (DT3010, HT10)

Transcription

1 Java for Interfaces and Networks (DT3010, HT10) Inner Classes Federico Pecora School of Science and Technology Örebro University Federico Pecora Java for Interfaces and Networks Lecture 8 1 / 16

2 Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 2 / 16

3 Inner classes (and interfaces) Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 3 / 16

4 Inner classes (and interfaces) What are inner classes? A normal class is a direct member of a package, a top-level class Inner classes are classes that nest within other classes available since Java 1.1 Inner classes come in four flavors: static member classes member classes local classes anonymous classes Federico Pecora Java for Interfaces and Networks Lecture 8 4 / 16

5 (Static) Member Classes Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 5 / 16

6 (Static) Member Classes (Static) Member classes Static member classes are classes that are static members of a class Like any other static member, they have access to all static members of the parent class A member class is also defined as a member of a class Unlike static member classes, the member class is instance specific Unlike static member classes, the member class has access to any and all methods and members this includes the parent s this reference Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

7 (Static) Member Classes (Static) Member classes (Static) Member classes have some restrictions A member class cannot have the same name as any of its enclosing classes Member classes cannot contain static fields, methods, or classes the only exception is for constants (i.e., declared both static and final) Member interfaces are implicitly static an interface cannot be instantiated, so there is nothing to associate with an instance of the enclosing class (see static member classes) Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

8 (Static) Member Classes (Static) Member classes MemberClassTest.java 1 public class MemberClassTest { 2 public void foo() { 3 System.out.println("Outer class FOO"); 4 } 5 public class MemberClass { 6 public void foo() { 7 System.out.println("Member class"); 8 } 9 public void test() { 10 this.foo(); 11 MemberClassTest.this.foo(); 12 } 13 } 14 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

9 (Static) Member Classes (Static) Member classes MemberClassTest.java 15 public static void main(string[] args) { 16 MemberClassTest o = new MemberClassTest(); 17 //Compilation error -- Needs an enclosing instance. 18 //MemberClassTest.MemberClass i = 19 // new MemberClassTest.MemberClass(); 20 MemberClassTest.MemberClass i = o.new MemberClass(); 21 i.test(); 22 } 23 } Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

10 (Static) Member Classes (Static) Member classes linux> java MemberClassTest Member class Outer class FOO linux> Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

11 (Static) Member Classes (Static) Member classes StaticMemberClassTest.java 1 public class StaticMemberClassTest { 2 public static void bar() { 3 System.out.println("Outer class BAR"); 4 } 5 public static class StaticMemberClass { 6 public void bar() { 7 System.out.println("Static Member class"); 8 } 9 public void test() { 10 this.bar(); 11 StaticMemberClassTest.bar(); 12 //Compilation error -- No enclosing instance! 13 //StaticMemberClassTest.this.bar(); 14 } 15 } 16 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

12 (Static) Member Classes (Static) Member classes StaticMemberClassTest.java 17 public static void main(string[] args) { 18 //Yes -- does not need an enclosing instance 19 StaticMemberClassTest.StaticMemberClass o1 = 20 new StaticMemberClassTest.StaticMemberClass(); 21 o1.test(); 22 } 23 } Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

13 (Static) Member Classes (Static) Member classes linux> java StaticMemberClassTest Static Member class Outer class BAR linux> Federico Pecora Java for Interfaces and Networks Lecture 8 6 / 16

14 (Anonymous) Local Classes Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 7 / 16

15 (Anonymous) Local Classes Local classes Local classes are classes that are declared within a block of code They are visible only within that block, just as any other method variable Like member classes, local classes are associated with a containing instance Local classes can access any member, including private members, of the containing class An anonymous class is a local class that has no name Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

16 (Anonymous) Local Classes Local classes A local class can never be used outside its block Local classes can access local variables, method parameters, or exception parameters that are Why? declared in the scope of the local method definition, and declared final the lifetime of a local class instance can be longer than the execution of the method in which the class is defined final ensures that its copy of a local variable and the original will always be the same Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

17 (Anonymous) Local Classes Local classes A local class cannot be declared public, protected, private, or static Local classes cannot contain static fields, methods, or classes the only exception is for constants that are declared both static and final Local interfaces are implicitly static A local class cannot have the same name as any of its enclosing classes Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

18 (Anonymous) Local Classes Local classes LocalClassTest.java 1 class A { protected char a = a ; } 2 class B { protected char b = b ; } 3 public class C extends A { 4 private char c = c ; 5 public static char d = d ; 6 public void createlocalobject(final char e) 7 { 8 final char f = f ; 9 int i = 0; 10 class Local extends B 11 { 12 char g = g ; 13 public void printvars() 14 {... } 15 } 16 Local l = new Local(); 17 l.printvars(); 18 } 19 } Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

19 (Anonymous) Local Classes Local classes LocalClassTest.java (Local.printVars()) 1 public void printvars() 2 { 3 System.out.println(g); //g is a field of Local 4 System.out.println(f); //f is a final local variable 5 System.out.println(e); //e is a final local parameter 6 System.out.println(d); //d is field of containing class 7 System.out.println(c); //c is field of containing class 8 System.out.println(b); //b is inherited by Local 9 System.out.println(a); //a is inherited by C 10 } Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

20 (Anonymous) Local Classes Local classes Are references to the local class instances destroyed when the enclosing method returns? Weird.java 1 public class Weird { 2 public static interface IntHolder { public int getvalue(); } 3 public static void main(string[] args) { 4 IntHolder[] holders = new IntHolder[10]; 5 for(int i = 0; i < 10; i++) { 6 final int fi = i; 7 class MyIntHolder implements IntHolder { 8 public int getvalue() { return fi; } 9 } 10 holders[i] = new MyIntHolder(); 11 } 12 for(int i = 0; i < 10; i++) 13 System.out.print(holders[i].getValue() + " "); 14 } 15 } Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

21 (Anonymous) Local Classes Local classes Are references to the local class instances destroyed when the enclosing method returns? linux> java Weird linux> The lexical scope of the methods of a local class has nothing to do with when the interpreter enters and exits the block of code that defines the local class Each instance of a local class has its own private copy of the scope within which it was created Federico Pecora Java for Interfaces and Networks Lecture 8 8 / 16

22 (Anonymous) Local Classes Anonymous classes An anonymous class is a local class that has no name An anonymous class definition is an expression it can be included as part of a larger expression, such as a method call Anonymous classes allow to define a one-shot class exactly where it is needed Anonymous classes have a succinct syntax that reduces clutter in your code Since anonymous classes are local classes, they share the same capabilities and limitations... although they cannot have constructors Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

23 (Anonymous) Local Classes Anonymous classes Code snippet - Local class 1 //... 2 public java.util.enumeration enumerate() { 3 //Enumerator as a local class 4 class Enumerator implements java.util.enumeration { 5 Linkable current; 6 public Enumerator() { current = head; } 7 public boolean hasmoreelements() { 8 return (current!= null); } 9 public Object nextelement() { 10 if (current == null) 11 throw new java.util.nosuchelementexception(); 12 Object value = current; 13 current = current.getnext(); 14 return value; 15 } 16 } 17 return new Enumerator(); 18 } 19 //... Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

24 (Anonymous) Local Classes Anonymous classes Code snippet - Anonymous class 1 //... 2 public java.util.enumeration enumerate() { 3 //Enumeration extended as part of the return statement 4 return new java.util.enumeration() { 5 Linkable current; 6 //Replace constructor with an instance initializer 7 { current = head; } 8 public boolean hasmoreelements() { 9 return (current!= null); } 10 public Object nextelement() { 11 if (current == null) 12 throw new java.util.nosuchelementexception(); 13 Object value = current; 14 current = current.getnext(); 15 return value; 16 } 17 }; //<-- Note the required semicolon (return statement) 18 } 19 //... Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

25 (Anonymous) Local Classes Anonymous classes So, when to use anonymous classes? An object of the anonymous class has no reason to exist in the absence of an object of the enclosing class An object of the anonymous class is not needed outside a method of the enclosing class Methods of the anonymous class need access to members of the enclosing class or local final variables/parameters Only one instance of the anonymous class is needed The class does not need a name that is accessible elsewhere in the program Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

26 (Anonymous) Local Classes Anonymous classes Anonymous classes are often used as adapters classes that define code that is invoked by some other object Code snippet (adapter class) 1 //... 2 File f = new File("/src"); //The directory to list 3 String[] filelist = f.list(new FilenameFilter() { 4 public boolean accept(file f, String s) { 5 return s.endswith(".java"); 6 } 7 }); //<-- Don t forget to end the method call! 8 //... list() method requires FilenameFilter argument FilenameFilter interface is implemented by an anonymous class (defiend within the method invocation) Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

27 (Anonymous) Local Classes Anonymous classes Defining an anonymous class is an implicit way to extend a class or implement an interface new FilenameFilter() {...} new <class-name> implements FilenameFilter {...} new Vector() {...} new <class-name> extends Vector {...} Notice that anonymous classes cannot have a contructor because they have no name... but you can pass parameters to the super-constructor and specify an instance initializer Code snippet (instance initializer) 1 universityregistration.addnames(new Vector(3) { 2 //Super-constructor is called, then instance initializer: 3 { add("heinz"); add("john"); add("anton"); } 4 }); //<-- End addnames method invocation Federico Pecora Java for Interfaces and Networks Lecture 8 9 / 16

28 (Anonymous) Local Classes Inner classes: summary Inner classes bring an object-oriented advantage a tree class has many helper methods that perform a search or walk of the tree from an object-oriented point of view, the tree is a tree, not a search algorithm however, you need intimate knowledge of the tree s data structures to accomplish a search encapsulate helper methods in an inner class Inner classes provide a means to accomplish namespaces Inner classes provide a means to accomplish callbacks anonymous classes are particularly fit for this purpose particularly useful in GUI creation Federico Pecora Java for Interfaces and Networks Lecture 8 10 / 16

29 Anonymous classes for GUIs Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 11 / 16

30 Anonymous classes for GUIs An ordinary GUI implementation SomeGUI.java 1 public class SomeGUI extends JFrame implements ActionListener { 2 protected JButton button1; 3 protected JButton button2; 4 //... 5 protected JButton buttonn; 6 public void actionperformed(actionevent e) { 7 if(e.getsource()==button1) { /* do something */ } 8 else if(e.getsource()==button2) { /* do something */ } 9 // else if(e.getsource()==buttonn) { /* do something */ } 11 } 12 // } Federico Pecora Java for Interfaces and Networks Lecture 8 12 / 16

31 Anonymous classes for GUIs An ordinary GUI implementation Our class SomeGUI implements ActionListener button press logic mingles with GUI implementation logic monolithic actionperformed() method There are N buttons in the worst case, the GUI will perform N comparisons Using inner classes, we could do away with chain of if blocks GUI always knows which code to execute O(1) instead of O(N) Using inner classes we can avoid that SomeGUI implements ActionListener Federico Pecora Java for Interfaces and Networks Lecture 8 12 / 16

32 Anonymous classes for GUIs An ordinary GUI implementation SomeGUI.java 1 //SomeGUI does NOT implement ActionListener 2 public class SomeGUI extends JFrame { 3 protected JButton button1; 4 protected JButton button2; 5 //... 6 protected JButton buttonn; 7 protected void buildgui() { 8 button1 = new JButton(); 9 button1.addactionlistener( 10 new ActionListener() { 11 public void actionperformed(actionevent e) { 12 /* do something */ 13 } 14 } 15 ); //<-- close addactionlistener method 16 // } 18 } Federico Pecora Java for Interfaces and Networks Lecture 8 12 / 16

33 Anonymous classes for GUIs An ordinary GUI implementation SomeGUI.java 1 //SomeGUI does NOT implement ActionListener 2 public class SomeGUI extends JFrame { 3 protected JButton button1; 4 protected JButton button2; 5 //... 6 protected JButton buttonn; 7 class Button1Handler implements ActionListener { 8 public void actionperformed(actionevent e) { 9 /* do something */ 10 } 11 } 12 // protected void buildgui() { 14 button1 = new JButton(); 15 button1.addactionlistener(new Button1Handler()); 16 // } 18 } Federico Pecora Java for Interfaces and Networks Lecture 8 12 / 16

34 Anonymous classes for GUIs An ordinary GUI implementation Better to use member classes or anonymous (local) classes? That is a question of style Also depends on application some buttons share functionality why re-write an anonymous class? just use an inner class! all buttons have very specific behavior why bother giving the class a name? just inline its definition! NB: Inner classes (especially anonymous classes) can get out of hand if too long! NB: If the class functionality makes sense outside the method, do not make it an anonymous class! Federico Pecora Java for Interfaces and Networks Lecture 8 12 / 16

35 Concrete examples Outline 1 Inner classes (and interfaces) 2 (Static) Member Classes 3 (Anonymous) Local Classes 4 Anonymous classes for GUIs 5 Concrete examples Federico Pecora Java for Interfaces and Networks Lecture 8 13 / 16

36 Concrete examples The BoringWindow A window with four buttons, each with a different behavior Tripp: prints Tripp! Trapp: prints Trapp! and a private instance variable of BoringWindow Trull/Hejsan: print Trull! / Hejsan!, a private instance variable of BoringWindow, and a local variable of BoringWindow s contructor Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

37 Concrete examples The BoringWindow Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

38 Concrete examples The BoringWindow TrippButtonListener.java 1 class TrippButtonListener implements ActionListener { 2 public void actionperformed(actionevent event) { 3 System.out.println("Tripp!"); 4 } 5 } //class TrippButtonListener TrippButtonListener can be a top-level class because it does not need to access any member/local variables The same is not true for the other three buttons... Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

39 Concrete examples The BoringWindow BoringWindow.java 1 public class BoringWindow { 2 private int bwx = 1; 3 private class TrappButtonListener 4 implements ActionListener { 5 public void actionperformed(actionevent event) { 6 System.out.println("Trapp!"); 7 System.out.println("bwx = " + bwx); 8 } 9 } //class TrappButtonListener 10 //continues... TrappButtonListener is a member class so it has access to private int bwx Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

40 Concrete examples The BoringWindow BoringWindow.java (cont.) 11 public BoringWindow() { 12 int kx = 2; 13 final int fkx = 3; 14 class TrullButtonListener implements ActionListener { 15 public void actionperformed(actionevent event) { 16 System.out.println("Trull!"); 17 System.out.println("bwx = " + bwx); 18 //Compilation error! 19 //local variable kx is accessed from within inner 20 //class; needs to be declared final 21 //System.out.println("kx = " + kx); 22 System.out.println("fkx = " + fkx); 23 } 24 } //class TrullButtonListener 25 //continues... TrullButtonListener is a local class so it has access to final int fkx (and private int bwx) Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

41 Concrete examples The BoringWindow BoringWindow.java (cont.) 26 JFrame frame = new JFrame("A boring window"); 27 frame.setsize(350, 50); 28 Container cp = frame.getcontentpane(); 29 cp.setlayout(new GridLayout(1, 4)); 30 JButton trippb = new JButton("Tripp!"); 31 JButton trappb = new JButton("Trapp!"); 32 JButton trullb = new JButton("Trull!"); 33 JButton hejsanb = new JButton("Hejsan!"); 34 cp.add(trippb); 35 cp.add(trappb); 36 cp.add(trullb); 37 cp.add(hejsanb); 38 trippb.addactionlistener(new TrippButtonListener()); 39 trappb.addactionlistener(new TrappButtonListener()); 40 trullb.addactionlistener(new TrullButtonListener()); 41 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

42 Concrete examples The BoringWindow BoringWindow.java (cont.) 42 hejsanb.addactionlistener(new ActionListener() { 43 public void actionperformed(actionevent event) { 44 System.out.println("Hejsan!"); 45 System.out.println("bwx = " + bwx); 46 //Compilation error! 47 //local variable kx is accessed from within inner 48 //class; needs to be declared final 49 //System.out.println("kx = " + kx); 50 System.out.println("fkx = " + fkx); 51 } 52 }); 53 frame.setvisible(true); 54 } //BoringWindow constructor 55 //continues... trullb s listener is an anonymous class, and has access to final int fkx (and private int bwx) Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

43 Concrete examples The BoringWindow BoringWindow.java (cont.) 56 public static void main(string[] args) { 57 final BoringWindow b = new BoringWindow(); 58 int mx = 4; 59 final int fmx = 5; 60 class UnusedButtonListener implements ActionListener { 61 public void actionperformed(actionevent event) { 62 System.out.println("Impossible!"); 63 //Compilation error! 64 //non-static variable bwx cannot be referenced 65 //from a static context 66 //System.out.println("bwx = " + bwx); 67 System.out.println("b.bwx = " + b.bwx); 68 //Compilation error! (as before) 69 //System.out.println("mx = " + mx); 70 System.out.println("fmx = " + fmx); 71 } 72 } //class UnusedButtonListener 73 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

44 Concrete examples The BoringWindow BoringWindow.java (cont.) 74 //Some useless instantiations of the button listeners 75 new TrippButtonListener(); 76 //Compilation error! 77 //non-static variable this cannot be referenced from 78 //a static context 79 //new TrappButtonListener(); 80 //Compilation error! 81 //cannot resolve symbol 82 //new TrullButtonListener(); 83 new UnusedButtonListener(); 84 } //main 85 } //class BoringWindow Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

45 Concrete examples The BoringWindow TrippButtonListener is a top-level class TrappButtonListener is a member class i.e., a non-static member which therefore cannot be accessed in main() if it were a static member class it would not make sense to instantiate it! TrullButtonListener is a local class and it is out of its scope HejsanB s listener has no name therefore it cannot be referenced outside the expression UnusedButtonListener is a local class (in scope) Federico Pecora Java for Interfaces and Networks Lecture 8 14 / 16

46 Concrete examples The ChatClient A multi-thread chat client with extra buttons Send insult: sends an insult to the server Send praise: sends a nice sentence to the server Close: closes the connection sending null to server and exiting (works with Server developed in lecture 5) Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

47 Concrete examples The ChatClient Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

48 Concrete examples The ChatClient ClientWithButtons.java 1 public class ClientWithButtons { 2 public static final int PORT = 2000; 3 private Socket socket; 4 private BufferedReader in; 5 private PrintWriter out; 6 BufferedReader kbd_reader; 7 //continues... We want our button listeners and server thread to have access to the socket (BufferedReader in and PrintWriter out) Therefore we will make them member classes Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

49 Concrete examples The ChatClient ClientWithButtons.java (cont.) 8 private class ServerListener extends Thread { 9 public void run() { 10 String linefromserver; 11 try { 12 while ((linefromserver = in.readline())!= null && 13!lineFromServer.equals("quit")) { 14 System.out.println("From server: " 15 + linefromserver); 16 } 17 } 18 catch (IOException e) { 19 System.out.println("Exception captured: " + e); 20 } 21 } 22 } //class ServerListener 23 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

50 Concrete examples The ChatClient ClientWithButtons.java (cont.) 24 private class ChatButtonWindow extends JFrame { 25 public ChatButtonWindow() { 26 super("extra chat buttons"); 27 Container cp = getcontentpane(); 28 cp.setlayout(new FlowLayout()); 29 JButton button1 = new JButton("Send insult"); 30 cp.add(button1); 31 JButton button2 = new JButton("Send praise"); 32 cp.add(button2); 33 JButton button3 = new JButton("Close"); 34 cp.add(button3); 35 setsize(200, 200); 36 setvisible(true); 37 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

51 Concrete examples The ChatClient ClientWithButtons.java (cont.) 38 button1.addactionlistener(new ActionListener() { 39 public void actionperformed(actionevent event) { 40 out.println("you ratbag!"); 41 System.out.println("Insult sent."); 42 } 43 }); 44 button2.addactionlistener(new ActionListener() { 45 public void actionperformed(actionevent event) { 46 out.println("you re the best!"); 47 System.out.println("Praise sent."); 48 } 49 }); 50 button3.addactionlistener(new ActionListener() { 51 public void actionperformed(actionevent event) { 52 System.out.println("Closed."); 53 System.exit(0); 54 } 55 }); 56 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

52 Concrete examples The ChatClient ClientWithButtons.java (cont.) 57 public ClientWithButtons(String servername) 58 throws IOException { 59 InetAddress addr = InetAddress.getByName(serverName); 60 Socket socket = new Socket(addr, PORT); 61 System.out.println("the new socket: " + socket); 62 in = new BufferedReader( 63 new InputStreamReader(socket.getInputStream())); 64 out = new PrintWriter( 65 new BufferedWriter( 66 new OutputStreamWriter( 67 socket.getoutputstream())), true); 68 kbd_reader = new BufferedReader( 69 new InputStreamReader(System.in)); 70 ServerListener t = new ServerListener(); 71 t.start(); 72 ChatButtonWindow w = new ChatButtonWindow(); 73 } //ClientWithButtons contructor 74 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

53 Concrete examples The ChatClient ClientWithButtons.java (cont.) 75 void listen() throws IOException { 76 String buf; 77 while (true) { 78 buf = kbd_reader.readline(); 79 System.out.println("From keyboard: " + buf); 80 System.out.println("To server: " + buf); 81 out.println(buf); 82 } 83 } 84 //continues... Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

54 Concrete examples The ChatClient ClientWithButtons.java (cont.) 85 public static void main(string[] args) throws IOException { 86 ClientWithButtons c; 87 if (args.length >= 1) 88 c = new ClientWithButtons(args[0]); 89 else 90 c = new ClientWithButtons(null); 91 c.listen(); 92 } //main 93 } //class ClientWithButtons Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

55 Concrete examples The ChatClient ClientWithButtons.java (cont.) 85 public static void main(string[] args) throws IOException { 86 ClientWithButtons c; 87 if (args.length >= 1) 88 c = new ClientWithButtons(args[0]); 89 else 90 c = new ClientWithButtons(null); 91 c.listen(); 92 } //main 93 } //class ClientWithButtons NB: out is used three nestings down: this can make code difficult to follow... Distance decreased with a local copy in ChatButtonWindow Tip: when too many levels, think about providing it through constructor/local copy Federico Pecora Java for Interfaces and Networks Lecture 8 15 / 16

56 Concrete examples Inner Classes Thank you! Federico Pecora Java for Interfaces and Networks Lecture 8 16 / 16