lect1 java oop-review

Software EngineeringFall 2014

Lecture 1: ReviewJava and OOP

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Review (1)

● An intermediate programming module● Programming:

● language: features & types● compiler & virtual machine

● Program:● verifiable● two levels: procedural, object oriented

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Review (2)

● Development techniques:● specification: design● implement: code● verify: reason about the correctness

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Topics at a glance

1) Introduction to Java

2) Overview of programming languages

Operational principles of compiler & VM

3) Verifiable program: design & implement

4) Principles of reasoning about programs

Reasoning about programs

5) Introduction to object oriented program

Class: design & implement

Class design issues

6) Basic ADTs

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Introduction to Java (1)

● Java programming environment● Basic program structure● Variable and types● Operations on primitive types● Object types:

● String● Enum● Array● Vector

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Introduction to Java (2)

● Text input/output● Flow of control● Programming concepts:

● decomposition● abstraction

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Decomposition

● The process of dividing a large problem into smaller ones

● the “divide and rule” principle

● Goal: decompose a program into smaller ones that interact in simple and well-defined ways

● Benefits:● eases problem solving● eases group work● eases program maintenance● eases understanding

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Decomposition criteria

● Each subproblem:● is at the same level of detail● can be solved independently

● The subproblems' solutions can be combined to solve the original problem

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Abstraction

● To look at a problem at a different level of detail● Helpful for simplifying a problem in attempt to

solve it ● Performed in tandem with decomposition at

increasing levels of detail

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Programming language abstractions

● Programming constructs that map more closely to how humans solve problems than machines

● Help simplify program development● Example: a search problem

determines if an element e is in an array a; if so returns true and an arbitrary index of e in a, otherwise returns false

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Example (1)

● One abstraction we know:

boolean found = false;for (int i = 0; i < a.length; i++) { if (a[i] == e) { z = i; found = true; }}

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Example (2)

● Yet another abstraction:

boolean found = a.isIn(e);

if (found) { z = a.indexOf(e);}

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Different types of abstraction

Which is simpler to program with

for (int i = 0; i < a.length; i++) { if (a[i] == e) { z = i; found = true; }}

for (int i = 0; i < a.length; i++) { if (a[i] == e) { z = i; found = true; }} boolean found = a.isIn(e);

if (found) { z = a.indexOf(e);}

boolean found = a.isIn(e); if (found) { z = a.indexOf(e);}

?What are the differences ?

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Programming language

● A compromise between:● programmer (PL user) and ● PL implementer

● Programmer:● language = means of expressing algorithms● conceptual clarity

● PL implementer:● language = means of instructing computers● implementation efficiency

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Procedure

public static float sum(float[] a) { int n = 0; float s = 0; while (n < a.length) { s = s + a[n]; n++; } return s;}

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Verifiable procedure

/** * determine the sum of array of real * numbers * @requires a is not null * @effects return the sum of the array * elements, i.e. result = * a[0]+...+a[a.length-1] */ public static float sum(float[] a) { //... code omitted ... }

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accummulated effects on n,s

update vars

With mid-conditions

public static float sum(float[] a) { int n = 0; float s = 0; for (n = 0; n < a.length; n++) { // 0 <= n < a.length /\ (n >=1 → // (n=n+1 /\ s = a[0] + ... + a[n-1])) s = s + a[n]; // s = a[0] + ... + a[n] } // n=a.length /\ s = a[0] + ... + a[n-1] return s;}

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(Verifiable) procedural program

/** * @overview a program that computes * the sum of real numbers *public class Sum { /** * the main procedure * * @effects prints the sum of an array of * real numbers obtained from the input * or 0 if no numbers were given */ public static void main(String[] args) { //... code omitted ... }

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...

/** * determine the sum of array of real * numbers * @requires a is not null * @effects return the sum of the array * elements, i.e. result = * a[0]+...+a[a.length-1] */ private static float sum(float[] a) { //... code omitted ... }

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...

/** * obtain an array of real numbers from a * pre-defined input source * @requires n > 0 * @effects return an array of n real * numbers or null if no real numbers * were found */

private static float[] getNumbers(int n) { //... code omitted ... }} // end Sum

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Object oriented program

● Design● logical design specification● physical design specification

● Implement:● write code that implement the physical specification

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Design

FloatArray

- array: float[]

+ FloatArray(float[])+ sum(): float+ getNumbers(int)

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General design concepts

attributes

operations

info. hiding

encapsulation

FloatArray

- array: float[]

+ FloatArray(float[])+ sum(): float+ getNumbers(int)

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Design concepts (1)

FloatArray

- array: Float[]

+ FloatArray(float[])+ sum(): float+ getNumbers(int)

[-1.0,0,1.0] [2.0,3.0] … FLOAT ARRAY

abstractconcept

class

formal type

object

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Design concepts (2)

FloatArray

- array: Float[]

type mutable optional length min max

Float[] T F

abstract properties(domain constraints)

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Other operations

FloatArray- array: float[]

+ FloatArray(int[])+ sum(): float+ getNumbers(int)+ toString(): String+ repOK(): boolean

default

validateimplementation

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Design concepts (3)

FloatArray

- array: float[] concrete type

representation

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Helper operations

FloatArray- array: float[]

+ FloatArray(float[])+ sum(): float+ getNumbers(int)- read(): float+ toString(): String+ repOK(): boolean

read a number from

keyboard

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Implementation

● Non-verifiable code● Verifiable code

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Non verifiable code

review.nonverifiable.FloatArray

CODE

Problem:● Usable but non-provable is it really FLOAT ARRAY?

● Why? lost all the design information

Solution:● Use design specification to capture design information

● (Add mid-conditions where appropriate)

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Design specification

FloatArraySpec

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Verifiable code

review.FloatArray

CODE

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Design issues

FloatArray- array: float[]

+ FloatArray(float[])+ ...+ getArray(): float[]

potentially exposing the rep

exposing the rep

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Application

review.FloatArrayApp

CODE

Other design issues:● Object initialisation● Object reference and usage● Stack and heap,● ...