Object Oriented Programming

Object Oriented Programming Lecture 4: Flow Control Mustafa Emre İlal emreilal@iyte.edu.tr

Recap • Implementation • Coding – writing source code • Assignment 2 • Circle class • Point class • Applications using these classes

Today • Flow control • Decision making • Loops • Thinking in Java – Chapter 3

Controlling Program Flow • Branching flow based on certain criteria • Conditional statements • Repeating a process – Loops

Normal Flow • A program is a series of commands • Step by step, top-down execution of commands • A pre-determined series is not adequate • Based on state, a different route might need to be taken • Need a branching mechanism - if

Including an optional additional path • Executing a set of commands based on certain conditions • Condition is of a boolean type in Java: either “true” or “false” Condition? false true

if … if (condition) { if condition is ‘true’ instructions to execute .... } instructions after merging of both branches (normal execution path)

Parallel Paths • The either/or situation: choosing one path or the other based on a condition. • if - else Condition? true false

if – else … if (condition) { instructions that are to be executed when the condition is true .... } else { instructions to be executed when the condition is false } instructions after merging of both branches

More than two paths • When more than two alternatives exist for a condition, we go through the list of possibilities. Elminating them one-by-one Condition1 true false Condition2 true false Condition3 true false

if – elseif if (condition1) { instructions to be executed if condition1 is true .... } elseif (condition2) { instructions to be executed if condition1 is false but condition2 is true } elseif (condition3) { instructions to be executed if all conditions above are false and condition3 is true } else { instructions to be executed if all conditions are false } instructions after merging of all branches

A different “condition testing” • .if – elseif command allows us to test conditions based on boolean value (true or false) • The switch statement allows us to test for various values of a particular variable type test value1 value2 value3 value4

switch switch (variable) { casevalue1: instructions; break; casevalue2: instructions; break; casevalue3: instructions; break; casevalue4: instructions; break; default: instructions; }

Repeating a process • Often a series of commands need to be repeated • Types of repetition: • An application itself is a mecahnism for repeating commands. • Function/method calls are repetitons based on demand • Loops: • A certain number of repetitons • Repetition until a condition is met

Loops Condition? false true Condition? true false

while while (test condition) { body of loop; } --- int i=0; while (i<10) { System.out.println(i); i++; }

do - while Do { body of loop; } while (test condition) ; --- int i=0; do { System.out.println(i); i++; } while (i<10) ;

for for (initialization[s]; test condition; counter update[s]) { body of loop; } ----- for (int i=0; i<10; i++) { System.out.println(i); }

enhanced for for (initialization[s] : iterable collection or array) { body of loop; } ----- for (int i :an_array[]) { System.out.println(i); }

break - continue • break • For immediate exit out of any loop body • Only one level exit in case of nested loops • continue • To start the next iteration of the loop immediately. • Only one level • If there is a need to go beyond one level, use “labels”.

break - continue while (true) { //infinite loop statements... ; if (exceptional condition) { break; //exit loop } more statements...; }

Assignment 04 • Write a class named ‘Assignment04’ that implements the following static methods. • static boolean isEven(int number) • if number is even, return true, otherwise return false • static String resolveAreaCode (int code) • Return the name of the area for the area codes below: • 212: Istanbul-1; 216: Istanbul-2; 312: Ankara; 232: Izmir; 322: Adana; 266: Balikesir; 224: Bursa; 462: Trabzon; 532: Turkcell; 542:Vodafone; 505-TurkTelekom; other codes: Unknown_code • (you are expected to use the switch statement)

Assignment 04 • static void fibonacciSeries(int n) • Display the first n numbers in the Fibonacci sequence (The sequence of numbers that start with 0 and 1 and where each number thereafter is the sum of the two preceeding numbers.) • static void fibonacciUntil (int max) • Display the fibonacci sequence that ends with the first number greater than or equal to max. • static void squares(int n) • Display the squares of the first n integers starting with 0. (02,12,22,32,...) • static void squaresUntil(int max) • Display the squares of integers that end with the first square greater than or equal to max.

Assignment 04 • static void randomTest() • The Math.random() method generates a real number n (of type double) where, 0.00 <= n < 1.00. Using this method, generate 1000 integers between 50 and 150 and display their average. • static void countdown(int n) • Display integers (in reverse order) from n down to 0.

Assignment 04 • Write a class named ‘Assignment04App’ • It should test all the static methods of the Assignment4 class and display the outputs on screen.

Next Week • Preperation: Thinking in Java Chapter 4-6

Object Oriented Programming