Introduction

Content

Apply

Reflect

Extend

Selection: `if'

Using pseudocode code we can illustrate how an if statement works. Consider the following pseudocode for a system to operate fire alarms in an office building:

if ( temperature too high )

sound the alarm

This illustrates the general form of an if statement, i.e.:

if <test>

action to perform if test is true

To implement our fire alarm pseudocode as a valid Java statement we could write the following:

if (temperature > 78)

soundAlarm();

(of course we are assuming the class has a variable called temperature and a method soundAlarm())

The way an if statement can cause deviation from the default sequential flow of execution can be illustrated as follows. Consider this pseudocode design:

statementA;

if( age > 60 )

statementB;

statementC;

If the variable age has a value over 60, say 65, then the test ( age > 60 ) will be true, and the therefore statementB will be executed. So the statements to be executed will be:

statementA

statementB

statementC

However, if the variable age has a value of 60 or less, say 21, then the test ( age > 60 ) will be false, and statementB will not be executed. So the statements executed will be:

statementA

statementC

Thus the result of a selection statement means that some statements may not be executed, or may be executed once.

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