COSC 1P03. Ch 6 Generics. Introduction to Data Structures 7.1

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Letitia Clarke
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1 Ch 6 Generics Introduction to Data Structures 7.1

2 Generic ADTs Behaviour of stack independent of type of item Generalize interface to allow any item type Generic Stack interface based on hypothetical content type E generalization (abstraction) over the content type changes from CharStack change from char to E throughout addition of generic parameter <E> after interface name E is a type variable Collections package set of collection ADTs (stack, queue, list, ) common names for exceptions NoSpaceException NoItemException Introduction to Data Structures 7.2

4 Parametric Types Stack is a parametric type Varies depending on the type name provided as actual type parameter With Stack<Character> charstack; as if E was replaced by Character Stack<Student> stdstack; as if E was replaced by Student Only need one interface to define both kinds of stacks class and interface declaration syntax scope of type_variable is the class or interface type syntax type_variable can be used wherever a reference_type used type_argument supplied for each type_parameter in generic type_argument must be a reference type (e.g. Character) Introduction to Data Structures 7.4

5 modifiers interface name [ < typeparam, > ] { } modifiers class name [ < typeparam, > ] [ implements interfacetype, ] { } public interface Stack < E > { } public class ConStack < E > implements Stack<E> { }

6 type < typeargument > name Stack<Character> charstack;

7 Generic Implementation Classes E.g. ConStack Compared to ConCharStack E substituted for char throughout ConStack is a parametric type implements Stack with same type parameter With charstack = new ConStack<Character>(8); have a stack of Character using the ConStack implementation stdstack= new ConStack<Student>(10); have a stack of Student using the ConStack implementation Introduction to Data Structures 7.7

10 Type Compatibility implements clause declares that the type_argument for Stack is whatever is supplied as type_argument for ConStack Thus and ConStack<Character> implements Stack<Character> ConStack<Student> implements Stack<Student> And so in Stack<Character> charstack; charstack = new ConStack<Character>(); is valid charstack = new ConStack<Student>(); is invalid Introduction to Data Structures 7.10

11 Type Checking How does the compiler type check within generic class, e.g. elts[top] = item; With ConStack<Character>, Character is substituted for E so this is OK How does compiler know? type_argument must be a reference_type all reference_types are subtypes of Object compiler type checks assuming type_variable is Object Thus the only operations available on the type_variable are those available on Object Note: compiler can still create the elts array since it knows it is an array of some reference type and thus each element is a reference (4 bytes) Introduction to Data Structures 7.11

12 Implementation Consecutive implementation note that in the constructor: elts = (E[]) new Object[size]; is used instead of the expected elts = new E[size]; Java does not allow a type_parameter to be used in an array creation expression creating an array of Object and downcasting it to E[] achieves the desired effect (unchecked cast warning) garbage collection in pop Linked implementation the generic Node class in the linked version, the Node class must also be parametric since the type of the content is unknown creation of a new Node is done via top = new Node<E>(item,top); Introduction to Data Structures 7.12

13 Client Class E.g. TestStacks Stack declared via: Stack<Character> s; Stack created using: s= new ConStack<Character>(100); Character pushed using s.push(c); note c is of type char but push has parameter type E Character Java automatically wraps c in a Character wrapper to provide type compatibility this is an autoboxing conversion as if the statement was s.push(new Character(c)); Introduction to Data Structures 7.13

14 character popped using out.writechar(s.pop()); note that pop returns type E Character while writechar takes type char Java automatically unwraps the char from the Character object to provide type compatibility this is an autounboxing conversion as if the statement was out.writechar(s.pop().charvalue()); Introduction to Data Structures 7.14

16 Ch 8 Queues Introduction to Data Structures 7.16

17 Queue A list (initially empty) of items (of some type) to which items may be added at one end (called the rear) and from which items may be removed at the other end (called the front) Examples waiting lines print queues Behaviour FIFO ordering Error conditions: underflow overflow Introduction to Data Structures 7.17

19 Queue Interface Generic E items to be stored Operations: enter (enqueue, add, insert) leave (dequeue, remove, delete) front (head, first) length (count, size) empty Exceptions NoItemException NoSpaceException Introduction to Data Structures 7.19

20 Queue ADT Contiguous Implementation Based on variable-sized array two indices: front & rear add at rear, remove at front queue moves towards rear repositioning on delete: O(n) circular array at end of array reuse front index modulo array size Introduction to Data Structures 7.20

22 Queue ADT Linked Implementation Sequentially-linked structure of items deletion from front insertion at end keep pointer to rear O(1) Length? keep count else O(n) Comparison with contiguous all operations O(1) space tradeoffs Introduction to Data Structures 7.22

1 P age DS & OOPS / UNIT II

1 P age DS & OOPS / UNIT II UNIT II Stacks: Definition operations - applications of stack. Queues: Definition - operations Priority queues - De que Applications of queue. Linked List: Singly Linked List, Doubly Linked List, Circular