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Control Statements

Lecture 6 from Chapter 5

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Three principles of OOP- Encapsulation

Encapsulation allows changes to code to be more easily made. It is because one can be confident that 'outsiders' are not relying on too many details. It has definition Creating a module to contain some algorithm or data structure, thus hiding its details behind the module's interface. http://www.csi.uottawa.ca:4321/java/index.html#nestedif-elsestatement

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3 principles of OOP- Inheritance and Polymorphism

Inheritance: It is a method for extending existing classes by adding methods and fields.Polymorphism: The behaviour varies depending on the actual type of an object.

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Review

Selection Statements If and switch

Iteration Statements While, do-while, for and nested

loops

Jump Statements Break, continue and return

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Selection Statements - If

If (condition) statement1; else statement2If condition is true, it will execute statement1 else statement2.Example

int a = 3, b = 4;if (a >b) a =1; // since a>b is false, it else b = 1 // will set b = 1

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Selection Statements – Nested Ifs

It is an if statement that is the target of another if or else.Exampleint a = 3, b = 4, c = 5;if (a >b) { //a >b

if (b > c) b = 1; //b > c, b = 1else c = 1; //b < c, c = 1}else a =1; // b > a, a = 1

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Example

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Example

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Selection Statement - switch

It is a multiway branch statement. It is similar to if-else-is, but is more well organized.

Switch (expression) {Case value1: //statement1Break;Case value2: //satement2Break…Default;//default statement

}

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Example – three cases

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Example with random value

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Example with advanced Switch

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Iteration Statements

WhileDo-whileForNested loop

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Iteration Statements - While

while(condition){// statements to keep executing while condition is true....

} Example

//Increment n by 1 until n is greater than 100while (n > 100) {n = n + 1;}

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Example – while

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Iteration Statements – do while

Do {// statements to keep executing while condition is true

} while(condition)It will first executes the statement and then evaluates the

condition.Example

int n = 5; Do {

System.out.println(“ n = “ + n);N--;

} while(n > 0);

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Example – difference between while and do-while

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Iteration Statements – for

for(initializer; condition; incrementer){// statements to keep executing while condition is true}  

Example

int i; int length = 10; for (i = 0; i < length; i++) { . . . // do something to the (up to 9 ) . . . }  

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Example – for-loop

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Multiple Initializers and Incrementers

Sometimes it's necessary to initialize several variables before beginning a for loop. Similarly you may want to increment more than one variable. Example

for (int i = 1, j = 100; i < 100; i = i+1, j = j-1) { System.out.println(i + j); }

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Nested Loop – Java allows loops to be nested

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Modification of nested loop

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Jump Statement

Three jump statementsBreak, continue and return

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Break and Continue with the nested loop

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Break as a form goto

A break statement exits a loop before an entry condition fails. The break statement can also be employed by itself to provide a form of “goto”. The format is:break label:

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Example – use break to exit from loop

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Continue - Explanation

Sometimes it is necessary to exit from the middle of a loop. Sometimes we want to start over at the top of the loop. Sometimes we want to leave the loop completely. For Examplefor (int i = 0; i < length; i++) { if (m[i] % 2 == 0) continue; // process odd elements... }

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Example - continue

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Return

It has purpose to exit from the current methodIt jumps back to the statement within the calling method that follows the original method call.

Examplereturn expression

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Example

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Summary

Selection Statements If and switch

Iteration Statements While, do-while, for and nested

loops

Jump Statements Break, continue and return