CHAPTER 2 COLLECTIONS Lecturer: Hồ Tiến Lâm Contents  Collection Interfaces  Concrete Collections  Legacy Collections 2 Created by Ho Tien Lam Contents  Collection Interfaces  Concrete Collections  Legacy Collections 3 Created by Ho Tien Lam Interfaces and Implementation  The Java collection library separates interfaces and implementations.  Let’s look at that separation with a familiar data structure, the queue . 4 data structure, the queue .  You use a queue when you need to collect objects and retrieve them in a FIFO order. Created by Ho Tien Lam Interfaces and Implementation (cont.)  A minimal form of a queue interface: interface Queue<E> { void add(E element); E remove(); 5  This interface tells you nothing about how the queue is implemented. There are two implementations of a queue. int size(); } Created by Ho Tien Lam Interfaces and Implementation (cont.)  One implementation uses a circular array and one uses a linked list. 6 Created by Ho Tien Lam Interfaces and Implementation (cont.)  When you use a queue in your program, you don’t need to know which implementation is actually used.  Use the interface type to hold the collection 7  Use the interface type to hold the collection reference. Created by Ho Tien Lam Queue<Customer> expressLane = new CircularArrayQueue<Customer>(100); expressLane.add(new Customer("Harry")); Interfaces and Implementation (cont.)  With this approach if you change your mind, you can easily use a different implementation.  You only need to change in one place, the constructor → save time of modification 8 constructor → save time of modification Created by Ho Tien Lam Queue<Customer> expressLane = new LinkedListQueue<Customer>(); expressLane.add(new Customer("Harry")); Interfaces and Implementation (cont.)  Among Java collection classes, there are some classes whose name begins with Abstract (AbstractQueue).  These classes are intended for library 9  These classes are intended for library implementors.  It is more convenient for developer to extend AbstractQueue than to implement Queue interface. Created by Ho Tien Lam Collection and Iterator Interfaces 10 public interface Collection<E> { boolean add(E element); Iterator<E> iterator(); } Created by Ho Tien Lam  add: adds an element to the collection. Returns true if adding the element actually changes the collection. Otherwise, returns false. } [...]... is an excellent design for a class framework Created by Ho Tien Lam Contents 20 Collection Interfaces Concrete Collections Legacy Collections Created by Ho Tien Lam Concrete Collections 21 Linked Lists Array Lists Hash Sets Tree Sets Priority Queues Maps Specialized Set and Map Classes Created by Ho Tien Lam Linked Lists 22 ArrayList class has a major drawback: Removing an element from the middle of... visit second element iter.remove(); // remove last visited element Created by Ho Tien Lam Linked Lists (cont.) 25 Example 1: Created by Ho Tien Lam Linked Lists (cont.) 26 The position-dependent add method is the responsibility of an iterator Using iterators to add elements makes sense only for collections that have a natural ordering There is no add method in the Iterator interface Instead, the library... Created by Ho Tien Lam Linked Lists (cont.) 29 If an iterator traverses a collection while another iterator is modifying it → confusing situation can occur See code as follows: List list = ; ListIterator iter1 = list.listIterator(); ListIterator iter2 = list.listIterator(); iter1.next(); iter1.remove(); // removes first element iter2.next(); // throws ConcurrentModificationException... that contains an add method Created by Ho Tien Lam Linked Lists (cont.) 27 The ListIterator interface: public interface ListIterator extends Iterator { void add(E e); boolean hasNext(); boolean hasPrevious(); ENJOY THE E next(); E previous(); DEMO… void remove(); void set(E e); } Created by Ho Tien Lam Linked Lists (cont.) 28 The add method: If the list has n elements, there are n+1 positions... cost of moving all elements beyond the removed one Created by Ho Tien Lam Linked Lists (cont.) 23 The linked list will solve this problem because a linked list stores each object in a separate link Each link also stores a reference to the next link in the sequence Created by Ho Tien Lam Linked Lists (cont.) 24 Example 1: List staff = new LinkedList(); // LinkedList implements List staff.add("Amy");... linked list to minimize the cost of insertion and removal If you want random access into a collection, use an array or ArrayList, not a linked list ENJOY THE DEMO… Created by Ho Tien Lam Concrete Collections 32 Linked Lists Array Lists Hash Sets Tree Sets Priority Queues Maps Specialized Set and Map Classes Created by Ho Tien Lam Array Lists 33 The ArrayList class also implements the List interface You... derived from the instance fields of an object Objects with different data yield different codes Table Hash Codes Resulting from the hashCode method of the String class String Hash Code “Lee” 7 626 8 “lee” 107 020 “eel” 100300 Created by Ho Tien Lam ... elements The Vector class also implements a growable array of objects We recommend that you use an ArrayList instead of a Vector whenever you don’t need synchronization Created by Ho Tien Lam Concrete Collections 34 Linked Lists Array Lists Hash Sets Tree Sets Priority Queues Maps Specialized Set and Map Classes Created by Ho Tien Lam Hash Sets 35 Linked lists and arrays let you specify the order in... returns an object that implements the Iterator interface You can use the iterator object to visit the elements in the collection one by one Created by Ho Tien Lam Collection and Iterator Interfaces (cont.) 12 public interface Iterator { E next(); boolean hasNext(); void remove(); } next: visits the elements one by one If you reach the end of collection, this method throws a NoSuchElementException hasNext: . CHAPTER 2 COLLECTIONS Lecturer: Hồ Tiến Lâm Contents  Collection Interfaces  Concrete Collections  Legacy Collections 2 Created by Ho Tien Lam Contents  Collection Interfaces  Concrete Collections . excellent design for a class framework. Contents  Collection Interfaces  Concrete Collections  Legacy Collections 20 Created by Ho Tien Lam . visit the elements in the collection one by one. } Collection and Iterator Interfaces (cont.) 12 public interface Iterator<E> { E next(); boolean hasNext(); void remove(); } Created by