Java for Interfaces and Networks (DT3029)

Transcription

1 Java for Interfaces and Networks (DT3029) Lecture 4 Networking with Threads and Containers Federico Pecora federico.pecora@oru.se Center for Applied Autonomous Sensor Systems (AASS) Örebro University, Sweden ContainerAlliance.com

2 The case for threads in client/server apps In the echo server example in the previous lecture, both client and server had a single thread server listens to on a port, and then gives all its attention to the first client that connects client is either reading form keyboard or sending/waiting for response from server Multi-threaded chat server a server through which multiple clients can chat server can serve many clients (i.e., has a thread that listens for connections) client has two threads: one for user input, one for communicating with the server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 2 / 29

3 Multi-threaded chat server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

4 Multi-threaded chat server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

5 Multi-threaded chat server MultiServer.java 1 public class MultiServer { 2 public static final int PORT = 2000; 3 public static void main(string[] args) throws IOException { 4 ServerSocket s = new ServerSocket(PORT); 5 System.out.println("Server socket: " + s); 6 System.out.println("Server listening..."); 7 try { while(true) { 8 // Blocks until a connection occurs: 9 Socket socket = s.accept(); 10 System.out.println("Connection accepted."); 11 System.out.println("The new socket: " + socket); 12 //continues F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

6 Multi-threaded chat server MultiServer.java (cont.) 13 try { 14 ClientThread t = new ClientThread(socket); 15 System.out.println("New thread started."); 16 System.out.println("The new thread: " + t); 17 } 18 catch(ioexception e) { 19 // If the constructor fails, close the socket, 20 // otherwise the thread will close it: 21 socket.close(); 22 } } } //catch, while, try 23 finally { s.close(); } 24 } //main 25 } //MultiServer 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

7 Multi-threaded chat server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

8 Multi-threaded chat server ClientThread.java 1 import...; 2 class ClientThread extends Thread { 3 private static int numberofclients = 0; 4 private static ArrayList<ClientThread> allclients = 5 new ArrayList<ClientThread>(); 6 private final int clientnumber = ++numberofclients; 7 private final Socket socket; 8 private final BufferedReader in; 9 private final PrintWriter out; 10 public ClientThread(Socket s) throws IOException { 11 socket = s; 12 in = new BufferedReader( 13 new InputStreamReader(socket.getInputStream())); 14 out = new PrintWriter( 15 new BufferedWriter( 16 new OutputStreamWriter( 17 socket.getoutputstream())), true); 18 //continues F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

9 Multi-threaded chat server ClientThread.java (cont.) 19 System.out.println("Client thread " + clientnumber + 20 " created."); 21 out.println("welcome. You are client number " + 22 clientnumber + "."); 23 allclients.add(this); 24 // If any of the above calls throw an 25 // exception, the caller is responsible for 26 // closing the socket. Otherwise the thread 27 // will close it. 28 start(); //Starts the thread, and calls run() 29 } 30 //continues F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

10 Multi-threaded chat server ClientThread.java (cont.) 31 public void run() { 32 try { 33 while (true) { 34 String inline = in.readline(); 35 System.out.println("Client thread " + clientnumber + 36 " received: " + inline); 37 if (inline == null inline.equals("quit")) break; 38 out.println("you said " + inline + " "); 39 Iterator<ClientThread> i = allclients.iterator(); 40 while (i.hasnext()) { 41 ClientThread t = i.next(); 42 if (t!= this) 43 t.out.println("from client " + clientnumber + 44 ": " + inline); 45 } } //while, while 46 System.out.println("Client thread " + clientnumber + 47 ": exiting..."); 48 } 49 //continues F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

11 Multi-threaded chat server ClientThread.java (cont.) 50 catch(ioexception e) { 51 System.out.println("Client thread " + clientnumber + 52 ": I/O error"); 53 } 54 finally { 55 try { socket.close(); } 56 catch(ioexception e) { 57 System.out.println("Client thread " + clientnumber + 58 ": Socket not closed!"); 59 } 60 allclients.remove(allclients.indexof(this)); 61 } //finally 62 } //run 63 } //class ClientThread 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

12 Multi-threaded chat server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

13 Multi-threaded chat server Client2.java 1 import...; 2 public class Client2 { 3 public static final int PORT = 2000; 4 public static void main(string[] args) throws IOException { 5 InetAddress addr; 6 if (args.length >= 1) 7 addr = InetAddress.getByName(args[0]); 8 else 9 addr = InetAddress.getByName(null); 10 Socket socket = new Socket(addr, PORT); 11 System.out.println("The new socket: " + socket); 12 BufferedReader in = new BufferedReader( 13 new InputStreamReader(socket.getInputStream())); 14 PrintWriter out = new PrintWriter( 15 new BufferedWriter( 16 new OutputStreamWriter( 17 socket.getoutputstream())), true); 18 //continues F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

14 Multi-threaded chat server Client2.java (cont.) 19 BufferedReader kbd_reader = new BufferedReader( 20 new InputStreamReader(System.in)); 21 ServerListener t = new ServerListener(in); 22 t.start(); 23 String buf; 24 while (true) { 25 buf = kbd_reader.readline(); 26 System.out.println("User input: " + buf); 27 System.out.println("To server: " + buf); 28 out.println(buf); 29 } 30 } //main 31 } //class Client F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

15 Multi-threaded chat server 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

16 Multi-threaded chat server ServerListener.java 1 import...; 2 final class ServerListener extends Thread { 3 final private BufferedReader fromserver; 4 public ServerListener(BufferedReader fromserver) { 5 this.fromserver = fromserver; 6 } 7 public void run() { 8 String linefromserver; 9 try { 10 while ((linefromserver = fromserver.readline())!= null 11 &&!linefromserver.equals("quit")) { 12 System.out.println("From server: " + linefromserver); 13 } 14 } 15 catch (IOException e) {... } 16 } //run 17 } //class ServerListener 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 3 / 29

17 What are containers? A container is an object that can contain other objects In Java 1.2 (Java 2) many new types of container classes were introduced, e.g., ArrayList Container classes can contain any type of object you have to cast to the object type when retrieving it Java provides a number of containers for lists, sets and maps list = an ordered collection of objects (interface List) set = a collection that contains no duplicate elements (interface Set) map = a mapping from keys to values, a look-up table (interface Map) All container classes extend class Collection 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 4 / 29

18 Common types of containers for lists Interface List: dynamic size, add to specific location, delete, search, iteration Class Vector (implements List): O(n) put/remove, O(1) get, thread-safe Class ArrayList (implements List): O(n) put/remove, O(1) get, non-thread-safe Class LinkedList (implements List): O(1) put/remove, O(n) get NB: primitive type arrays have fixed size and are simplest, but fastest (if you know what you are doing)... and you can use the convenience methods of class Arrays 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 5 / 29

19 Common types of containers for sets Interface Set: dynamic size, add, delete, search, iteration Class HashSet (implements Set): an un-sorted set (implemented as a HashMap), O(1) get/put, O(n) remove Class TreeSet (implements Set): a sorted set (implemented as a TreeMap), O(log(n)) get/put/remove 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 6 / 29

20 Common types of containers for mappings Interface Map: dynamic size, add, delete, search, iteration Class HashMap (implements Map): Hash table based implementation of the Map interface, O(1) get/put, O(n) remove Class TreeMap (implements Map): binary tree based implementation of the Map interface, O(log(n)) get/put/remove 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 7 / 29

21 Containers: overview 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 8 / 29

22 Containers: package java.util import java.util.arraylist; import java.util.iterator; import java.util.linkedlist; import java.util.hashset; import java.util.treeset; import java.util.hashmap; import java.util.treemap; Containers cannot contain primitive types (except primitive type arrays) Containers can contain any kind of Object Underlying implementation of Vector and ArrayList is an array 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 9 / 29

23 Containers: primitive type arrays The built-in arrays are easiest, and sometimes the Java API imposes their use 1 public static void main(string[] args) { 2 for (int i = 0; i < args.length; ++i) 3 System.out.println("Arg. " + i + ": " + args[i] + " "); 4 } 5 } Arrays need to be allocated with new 1 int[] intarray1 = new int[10]; 2 int intarray2[] = new int[10]; 3 String[] fruits = { "Apple", "Pear", "Orange" }; 4 int intarray[10]; // Compilation error: ] expected 5 fruits = new String[] { "Pineapple", "Banana" }; 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 10 / 29

24 Convenience methods in class Arrays java.util.arrays provides convenient methods for manipulating arrays 1 java.util.arrays.sort(fruits); 2 java.util.arrays.fill(fruits, "Lemon"); You can also make arrays of non-primitive types 1 Hamster[] ha1 = 2 { new Hamster("Adam"), new Hamster("Bertil"), 3 new Hamster("Kate") }; 4 for (int i = 0; i < ha1.length; ++i) 5 System.out.println("ha1[" + i + "]: " + ha1[i] + " "); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 11 / 29

25 Convenience methods in class Arrays Assuming we have defined tostring() in class Hamster... linux> java HamsterTest ha1[0]: Hamster-Adam ha1[1]: Hamster-Bertil ha1[2]: Hamster-Kate You can also allocate arrays first and then fill them in 1 Hamster[] ha2 = new Hamster[4]; 2 ha2[0] = new Hamster("Anna"); 3 ha2[1] = new Hamster("Beata"); 4 ha2[2] = new Hamster("Cecilia"); 5 ha2[3] = new Hamster("Dora"); 6 ha2[4] = new Hamster("Fredrik"); // Runtime exception 7 ha2[2] = new Boat("Titanic"); // Compilation error 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 12 / 29

26 Convenience methods in class Arrays Assuming we have defined compareto() in class Hamster... 1 Arrays.sort(ha1); 2 Arrays.sort(ha2); Assuming we have defined equals() in class Hamster... 1 if (Arrays.equals(ha1, ha2)) 2 System.out.println("The two arrays are equal"); 3 else if (ha1.length == ha2.length) 4 System.out.println("There is at least one pair 5 of different elements"); 6 else 7 System.out.println("The two arrays have 8 different lengths"); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 13 / 29

27 A different kind of array : ArrayList ArrayLists are a better choice if one needs a dynamic array, i.e., an array whose size can increase or decrease during execution When instantiated, the list is empty, and objects are added through the add() method The get() method retrieves objects in a given position 1 ArrayList<Boat> boats = new ArrayList<Boat>(); 2 Boat b1 = new Boat("Titanic"); 3 Boat b2 = new Boat("Exxon Valdez"); 4 Boat b3 = new Boat("Torrey Canyon"); 5 boats.add(b1); 6 boats.add(b2); 7 boats.add(b3); 8 boats.add(b1); 9 boats.add(b1); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 14 / 29

28 A different kind of array : ArrayList ArrayLists are a better choice if one needs a dynamic array, i.e., an array whose size can increase or decrease during execution When instantiated, the list is empty, and objects are added through the add() method The get() method retrieves objects in a given position 1 System.out.println("Boats (1):"); 2 for (int i = 0; i < boats.size(); ++i) 3 System.out.println(" boats[" + i + "]: " + boats.get(i)); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 14 / 29

29 A different kind of array : ArrayList ArrayLists are a better choice if one needs a dynamic array, i.e., an array whose size can increase or decrease during execution When instantiated, the list is empty, and objects are added through the add() method The get() method retrieves objects in a given position linux> java BoatTest Boats (1): boats[0]: Boat Titanic boats[1]: Boat Exxon Valdez boats[2]: Boat Torrey Canyon boats[3]: Boat Titanic boats[4]: Boat Titanic 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 14 / 29

30 A different kind of array : ArrayList Instead of using an int to cycle through the ArrayList and retrieve elements with get(), we can use an Iterator Iterators provide methods hasnext() and next() to access elements in the ArrayList 1 System.out.println("Boats (2):"); 2 Iterator i1 = boats.iterator(); 3 while (i1.hasnext()) 4 System.out.println(" A boat: " + i1.next()); We can for instead of while to limit the scope of the iterator to the loop 1 System.out.println("Boats (3):"); 2 for (Iterator i = boats.iterator(); i.hasnext(); ) 3 System.out.println(" A boat: " + i.next()); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 15 / 29

31 A different kind of array : ArrayList Instead of using an int to cycle through the ArrayList and retrieve elements with get(), we can use an Iterator Iterators provide methods hasnext() and next() to access elements in the ArrayList 1 System.out.println("Boats (2):"); 2 Iterator i1 = boats.iterator(); 3 while (i1.hasnext()) 4 System.out.println(" A boat: " + i1.next()); Even more practical: we can use the for-each loop 1 System.out.println("Boats (4):"); 2 for (Boat i : boats) { 3 System.out.println(" A boat: " + i); 4 } 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 15 / 29

32 A different kind of array : ArrayList The method indexof() returns the index of the first occurrence of an object, or -1 if the object is not found in the list Comaprison depends on implementation of equals() Hamster.java 1 class Hamster { public boolean equals(object o) { 4 if (!(o instanceof Hamster)) return false; 5 return (o.getname().equals(this.name)); 6 } } 1 System.out.println("Hasse s position (1): " + 2 hamsters.indexof(hasse)); 3 System.out.println("Hasse s position (2): " + 4 hamsters.indexof(new Hamster("Hasse"))); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 16 / 29

33 A different kind of array : ArrayList The method remove() deletes an object from the list The object can be indicated both by index and by reference The latter depends on implementation of equals() Hamster.java 1 class Hamster { public boolean equals(object o) { 4 if (!(o instanceof Hamster)) return false; 5 return (o.getname().equals(this.name)); 6 } } 1 // Remove element in position 4 2 boats.remove(4); 3 // Remove the first occurrence of boat Titanic 4 boats.remove(b1); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 17 / 29

34 ArrayList vs. Vector The two classes are almost identical if seen from the outside Nonetheless, some significant differences are present synchronization: Vectors are synchronized, ArrayLists are not the latter are slightly faster data growth: inserting an element into either type of objectcan trigger an expansion of the internal array size a Vector doubles the size of its array, while the ArrayList increases its array size by 50% Note that all methods and usage patterns shown for ArrayList work for Vector! 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 18 / 29

35 Containers and generics Container classes can contain any type of object You have to cast to the object type when retrieving it Java 1.5 (Java 5.0) introduced generics No generics 1 // Removes 4-letter words from c. Elements must be strings 2 static void expurgate(arraylist c) { 3 for (Object o : c) 4 if (((String) o).length() == 4) 5 c.remove(o); 6 } Inconvenient to have to cast all the time The compiler cannot check that you are casting to the right type 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 19 / 29

36 Containers and generics Generics provides a way for you to communicate the type of a collection to the compiler Avoids the need to cast With generics 1 // Removes 4-letter words from c. 2 static void expurgate(arraylist<string> c) { 3 for (String o : c) 4 if (o.length() == 4) 5 c.remove(o); 6 } Code using generics is safer and clearer eliminates an unsafe cast moves part of the specification of the method from a comment to its signature 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 20 / 29

37 A different kind of array : LinkedList Both ArrayList and LinkedList implement the interface List They have the same methods, but differ in performance The internal representation of LinkedList is, though, very different from that of ArrayList and Vector 1 // A LinkedList is like an ArrayList 2 LinkedList<Boat> boatlist = new LinkedList<Boat>(); 3 for (Iterator<Boat> i = boats.iterator(); i.hasnext(); ) 4 boatlist.add(i.next()); 5 boatlist.addall(boats); // All at once! 6 System.out.println("Boats in the boatlist:"); 7 for (Iterator<Boat> i = boatlist.iterator(); i.hasnext(); ) 8 System.out.println(" A boat: " + i.next()); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 21 / 29

38 Sets with class HashSet A set cannot contain doubles Elements in a set are not ordered... well, they are ordered because you insert them is a specific order, but you have no guarantee that this order is maintained in the internal representation! Both HashSet and TreeSet implement the interface Set the two classes can do the same things, but have different performance 1 // A HashSet is a set, so no duplicates 2 HashSet<Boat> boatset = new HashSet<Boat>(); 3 for (Iterator<Boat> i = boats.iterator(); i.hasnext(); ) 4 boatset.add(i.next()); 5 boatset.addall(boats); // All at once! 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 22 / 29

39 Sets with class HashSet A set cannot contain doubles Elements in a set are not ordered... well, they are ordered because you insert them is a specific order, but you have no guarantee that this order is maintained in the internal representation! Both HashSet and TreeSet implement the interface Set the two classes can do the same things, but have different performance 1 System.out.println("Boats in the boatset:"); 2 for (Iterator<Boat> i = boatset.iterator(); i.hasnext(); ) 3 System.out.println(" A boat: " + i.next()); 4 boatset.remove(b1); 5 System.out.println("After removal from boatset:"); 6 for (Iterator<Boat> i = boatset.iterator(); i.hasnext(); ) 7 System.out.println(" A boat: " + i.next()); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 22 / 29

40 Sets with class HashSet A set cannot contain doubles Elements in a set are not ordered... well, they are ordered because you insert them is a specific order, but you have no guarantee that this order is maintained in the internal representation! Both HashSet and TreeSet implement the interface Set the two classes can do the same things, but have different performance linux> java BoatTest Boats in the boatset: A boat: Boat Titanic A boat: Boat Exxon Valdez A boat: Boat Torrey Canyon After removal from boatset: A boat: Boat Exxon Valdez A boat: Boat Torrey Canyon 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 22 / 29

41 Another type of set: TreeSet Both HashSet and TreeSet implement the interface Set They have the same methods, but differ in performance TreeSet maintains data as a binary tree, thus making it suited for binary tree search thus, Objects inserted into a TreeSet should implement the interface Comparable (in order to have the method compareto()) 1 HashSet<Phonenumber> phonenumberset1 = 2 new HashSet<Phonenumber>(); 3 phonenumberset1.add(new Phonenumber(116090)); 4 phonenumberset1.add(new Phonenumber(271010)); 5 phonenumberset1.add(new Phonenumber(271011)); 6 phonenumberset1.add(new Phonenumber(271012)); 7 phonenumberset1.add(new Phonenumber(111111)); 8 phonenumberset1.add(new Phonenumber(111111)); 9 phonenumberset1.add(new Phonenumber(111111)); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 23 / 29

42 Another type of set: TreeSet Both HashSet and TreeSet implement the interface Set They have the same methods, but differ in performance TreeSet maintains data as a binary tree, thus making it suited for binary tree search thus, Objects inserted into a TreeSet should implement the interface Comparable (in order to have the method compareto()) 1 System.out.println("Phonenumber in phonenumberset 1:"); 2 for (Iterator<Phonenumber> i = 3 telephonenumberset1.iterator(); i.hasnext(); ) 4 System.out.println(" A phonenumber: " + i.next()); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 23 / 29

43 Another type of set: TreeSet Both HashSet and TreeSet implement the interface Set They have the same methods, but differ in performance TreeSet maintains data as a binary tree, thus making it suited for binary tree search thus, Objects inserted into a TreeSet should implement the interface Comparable (in order to have the method compareto()) linux> java PhonenumeberTest Phonenumber in phonenumberset 1: A phonenumber: +46-(0) A phonenumber: +46-(0) A phonenumber: +46-(0) A phonenumber: +46-(0) A phonenumber: +46-(0) F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 23 / 29

44 Mappings with class HashMap A mapping (or map) is sometimes calle a dictionary or a look-up table Every elements in a mapping consists of a key and a value Knowing the key allows to obtain the value quickly 1 HashMap<String, Phonenumber> phnbk = 2 new HashMap<String, Phonenumber>(); 3 phnbk.put("anna", new Phonenumber(116090)); 4 phnbk.put("bengt", new Phonenumber(224000)); 5 phnbk.put("conny", new Phonenumber(125566)); 6 phnbk.put("doris", new Phonenumber(171045)); 7 phnbk.put("eberhart", new Phonenumber(111111)); 8 phnbk.put("eberhart", new Phonenumber(222222)); 9 phnbk.put("eberhart", new Phonenumber(333333)); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 24 / 29

45 Mappings with class HashMap A mapping (or map) is sometimes calle a dictionary or a look-up table Every elements in a mapping consists of a key and a value Knowing the key allows to obtain the value quickly 1 System.out.println("Conny s number " + phnbk.get("conny")); 2 System.out.println("Phonebook 1:"); 3 for (Iterator<String> i = phnbk.keyset().iterator(); 4 i.hasnext(); ) { 5 String namn = i.next(); 6 System.out.println(" " + name + " s number: " + 7 phnbk.get(name)); 8 } 9 System.out.println("Phonebook 1, again:"); 10 for (String i : phnbk.keyset()) { 11 System.out.println(" " + i + " s number: " + phnbk.get(i)); 12 } 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 24 / 29

46 Mappings with class HashMap A mapping (or map) is sometimes calle a dictionary or a look-up table Every elements in a mapping consists of a key and a value Knowing the key allows to obtain the value quickly Conny s number: +46-(0) Phonebook 1: Doris s number: +46-(0) Eberhart s number: +46-(0) Conny s number: +46-(0) Bengt s number: +46-(0) Anna s number: +46-(0) Phonebook 1, again: Doris s number: +46-(0) Eberhart s number: +46-(0) Conny s number: +46-(0) Bengt s number: +46-(0) Anna s number: +46-(0) F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 24 / 29

47 Another type of map: TreeMap Both HashMap and TreeMap implement the interface Map They have the same methods, but differ in performance TreeMap maintains data as a binary tree, thus making it suited for binary tree search thus, Objects inserted into a TreeMap should implement the interface Comparable (in order to have the method compareto()) 1 // String implements Comparable... 2 TreeMap<String, Phonenumber> phnbk1 = 3 new TreeMap<String, Telefonnummer>(); 4 phnbk1.put("anna", new Phonenumber(116090)); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 25 / 29

48 Primitive types in containers Java containers cannot contain primitive types (except for primitive arrays) 1 // Compilation error: "unexpected type" 2 ArrayList<int> numbers = new ArrayList<int>(); But Java provides boxed variants of primitive types int Integer long Long float Float double Double boolean Boolean byte Byte F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 26 / 29

49 Auto-boxing and Auto-unboxing When inserting into a container, you would need to instantiate the boxed type from your primitive type 1 ArrayList<Integer> numbers = new ArrayList<Integer>(); 2 int[] numberarray = { 5, 3, 7, 12, 4 }; 3 for (int i : numberarray) 4 numbers.add(new Integer(i)); When you retrieve you would need to use xxxvalue() method... 1 int[] numberarray = new int[numbers.size()]; 2 for (int i = 0; i < numbers.size(); i++) 3 numberarray[i] = numbers.get(i).intvalue(); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 27 / 29

50 Auto-boxing and Auto-unboxing Auto-boxing allows you to avoid instantiating the boxed type 1 ArrayList<Integer> numbers = new ArrayList<Integer>(); 2 int num4 = 4; 3 numbers.add(num4); 4 numbers.add(5); Auto-unboxing allows you to avoid calling a method 1 System.out.println("Numbers in ArrayList<Integer>:"); 2 for (int i : numbers) 3 System.out.println(" A number " + i); 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 28 / 29

51 Networking with Threads and Containers Thank you! 2014 F. Pecora, T.P. McCarthy / Örebro University aass.oru.se 29 / 29