Generics Concurrency Exceptions (examples in C++, Java, & Ada)

Transcription

1 Generics Concurrency Exceptions (examples in C++, Java, & Ada)

2 Generic Programming Definition (WikiPedia): Generic programming is a style of computer programming in which algorithms are written in terms of to-be-specified-later types that are then instantiated when needed for specific types provided as parameters.

3 Generics in C++ (Templates) Uses the Standard Template Library (STL) Provides: containers (e.g., class, data structure), iterators (objects to traverse collection of items), algorithms Reference: Standard_Template_Library Uses Templates : feature that allows functions and classes to operate with generic types to avoid having to rewrite the function or class for different data types. Two kinds of templates: Function templates function that can have arguments of different types. Class templates used to implement containers, and is instantiated by passing a given set of types as template arguments.

4 Generics in C++ (Templates) Sample function template: template<class T> T min(t arg1,t arg2,t arg3) { T v; if((arg1<arg2)&&(arg2<arg3)) v=arg1; else if((arg2<arg1)&&(arg2<arg3)) v=arg2; else v=arg3; return v; ;

5 Generics in C++ (Templates) Called like an ordinary function. The compiler examines the arguments used to call the function, and then instantiates a version of the function parameritizing T for the type passed: For example, if make the following call: min(100,200,300); The version generated will be: int min(int arg1,int arg2,int arg3) { Can call the same function with any data type: int, char, double.

6 Generics in C++ (Templates) Using a Container (List): Example: template< data_t> list<data_t>class::list(data_t d) { data=d; next=0;

7 Generics in Java Added to Java later. Allows a method to operate on objects of various types. Hierarchy and Classification (WikiPedia): A type variable is an unqualified identifier. Type variables are introduced by generic class declarations, generic interface declarations, generic method declarations, and by generic constructor declarations. A class is generic if it declares one or more type variables that act as parameters. An interface is generic if it declares one or more type variables as the type parameters of the interface. A method is generic if it declares one or more type variables as the formal type parameters of the method. A constructor can be declared as generic, independently of whether the class the constructor is declared in is itself generic as the formal type parameters of the constructor.

8 Generics in Java Example: class Gen<T> { T ob; // declare an object of type T Gen(T o) { ob = o; T getob() { return ob; void showtype() { System.out.println("Type of T is " + ob.getclass().getname());

9 Generics in Java Class with two generics: class TwoGen<T, V> { T ob1; V ob2; TwoGen(T o1, V o2) { ob1 = o1; ob2 = o2; void showtypes() { System.out.println("Type of T is " + ob1.getclass().getname()); System.out.println("Type of V is " + ob2.getclass().getname()); T getob1() { return ob1; V getob2() { return ob2;

10 Generics in Java Wildcards: Java allows the use of wildcards to specify bounds on the type of parameters a given generic object may have. (WikiPedia) Wildcards are type parameters of the form "?", possibly annotated with a bound.

11 Generics in Java Wildcard Example: class Stats<T extends Number> { T[] nums; // array of Number or subclass // Pass the constructor a reference to // an array of type Number or subclass. Stats(T[] o) { nums = o; Reference to Number (Abstract Class): download.oracle.com/javase/1.5.0/docs/api/java/lang/ Number.html

12 Concurrency Definition (WikiPedia): Concurrent computing is a form of computing in which programs are designed as collections of interacting computational processes that may be executed in parallel.

13 Concurrency in Java Thread class in Java: download.oracle.com/javase/1.5.0/docs/api/ java/lang/thread.html ThreadGroup class in Java: download.oracle.com/javase/1.4.2/docs/api/ java/lang/threadgroup.html

14 Concurrency in Ada Basic unit of concurrency in Ada is a task. Tasks are declared and have a Task Body. Tasks begin once they are created Tasks are not called, unlike Functions and Procedures. Tasks can communicate with other tasks: Tasks can pass messages (message passing) Tasks can share variables (shared memory)

15 Concurrency in Ada Example: task type Messenger is entry Start(Message : in String); end Messenger; task body Messenger is use Ada.Numerics.Float_Random; Seed : Generator; Msg : Bounded_String; begin accept Start(Message : in String) do Msg := To_Bounded_String(Message); end Start; Reset(Seed); delay Duration(Random(Seed)); Ada.Text_Io.Put_Line(To_String(Msg)); end Messenger;

16 Exceptions Definition (WikiPedia): Exception handling is a programming language construct designed to handle the occurrence of exceptions, special conditions that change the normal flow of program execution.

17 Exceptions in C++ Try/Catch: try { for (int n=0; n<=10; n++) { if (n>9) throw "Out of range"; myarray[n]='z'; cout<<myarray[n]<<" "; catch (char const * str) { cout << "Exception: " << str << endl;

18 Exceptions in Java Exceptions are objects descended from Throwable. Partial Family of Throwable: jw-07-exceptions.html

19 Exceptions in Java Example: class MyException extends Exception { public MyException() { super(); public MyException(String s) { super(s); try { b(i); catch (MyException e) { // Here we handle MyException