CSC/ECE 517 Fall 2011/ch1 1e dm

CSC/ECE 517 Fall 2011/ch1 1e dm

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Introduction

This wiki article describes the block structured and object oriented languages. It also highlights their advantages and limitations along with providing the comparison between them.

Block Structured Languages

A block is a section of code which can be grouped together. Blocks consist of one or more declarations and statements. A block structured programming language uses and permits the creation of blocks and nested blocks. The major function of using blocks is to enable the groups of statements within the block to be treated as if they were a single statement.

Structured programming is a technique for organizing and coding computer programs in which a hierarchy of modules is used, each having a single entry and a single exit point, and in which control is passed downward through the structure without unconditional branches to higher levels of the structure. A structured program is decomposed into a hierarchy of processes. A process in this context is a body of code, typically a function or subroutine, that takes some input and manipulates it to produce an output. A process may be composed of other, more specialized processes, i.e., it may be a function that calls other functions. Structured Programming uses three types of control flow: sequential, test, and iteration.

Examples of block structured programming languages are ALGOL, FORTAN, Pascal, C, Python, Lisp.

Characteristics

• It takes on the top-to-bottom approach.
• It is based around data structures and subroutines.
• It uses single entry and exit block.
• The names of variables and other objects such as procedures which are declared in outer blocks are visible inside other inner blocks, unless they are shadowed by an object of the same name.
• It splits the tasks into modular forms.

Advantages

• Splitting of tasks into blocks/modules makes the program simpler and easier to read with less lines and codes.
• In a solution space where there are widely varying spatial and temporal scales one can
• Put more grid where the solution is more interesting.
• Leave the solution coarse where the solution is not interesting.
• Can save an order of magnitude in memory.
• Can save an order of magnitude in run time.
• Numerical accuracy improves with more grid where gradients are strongest.
• Being block-structured allows Fortran to be used for array operations.
• Overhead involved involved in coarse-fine interactions can be amortized over larger array calculations.
• Numerical accuracy is improved if the coarse-fine interface is kept to a codimension smaller than the solution.

Limitations

• Communication patterns between levels can be complex.
• Algorithm complexity can be substantial.
• No data abstraction or information hiding supported.

Object Oriented Languages

An approach to programming in which each data item with the operations used on it is designated as an object; the routines used to operate on the data item are called methods; and objects are grouped in a hierarchy of classes, with each class inheriting characteristics from the class above it.

Programming techniques may include features such as data abstraction, encapsulation, messaging, modularity, polymorphism, and inheritance.

Examples of object oriented programming languages are C++, Java, Smalltalk, Ruby.

Characteristics

• This type of programming uses sections in a program to perform certain tasks.
• It splits the program into objects that can be reused into other programs.
• They are small programs that can be used in other software.
• Each object or module has the data and the instruction of what to do with the data in it. This can be reused in other software .
• An object-oriented program is decomposed into a network of collaborating objects. An object represents a thing or concept and has a known set of behaviors that may be invoked by other objects. For any activity of the program, an object responsible for that activity may interact with other objects by invoking their behaviors, or "methods", until the activity is complete.

Advantages

• Simplicity: software objects model real world objects, so the complexity is reduced and the program structure is very clear.
• Modularity: each object forms a separate entity whose internal workings are decoupled from other parts of the system.
• Modifiability: it is easy to make minor changes in the data representation or the procedures in an OO program. Changes inside a class do not affect any other part of a program, since the only public interface that the external world has to a class is through the use of methods. *Extensibility: adding new features or responding to changing operating environments can be solved by introducing a few new objects and modifying some existing ones.
• Maintainability: objects can be maintained separately, making locating and fixing problems easier.
• Re-usability: objects can be reused in different programs.
• Helps to reduce large problems to smaller, more manageable problems.

Limitations

• Over generalization
• Artificial class relations
• Unnecessary complications