Transcript If-statements & Indefinite Loops CSE 115 Spring 2006

If-statements &
Indefinite Loops
CSE 115
Spring 2006
April 24, 26, & 28 2006
Selection
 Choice in a program.
 We’ve seen polymorphism already as a
mechanism for a way for a program to
behave differently under different
conditions.
 There is another construct for selection
built into Java: if-statements.
If-statements
 Syntax
if (booleanExpression) {
//code executed if boolean
//Expression is true
}
If-else statements
if (booleanExpression) {
//code executed if boolean
//Expression is true
}
else {
//code executed if boolean
//Expression is false
}
If-else statements (more
than two choices)
if (booleanExpression1) {
//code executed if boolean
//Expression1 is true
}
else if (booleanExpression2) {
//code executed if boolean
//Expression2 is true
}
else {
//code executed if neither boolean
//Expression1 or booleanExpression2 is
//true
}
Loops
(Iteration/Repetition)
 The ability to do a task repeatedly.
 The functionality of repetition is most
often implemented in programming
languages using loops.
Indefinite Loop
 There are two types of indefinite loops
built into Java, the while-loop and the dowhile-loop. An indefinite loop is normally
used when you do not know how many
times you want a specific task to be
performed.
Entry vs. Exit Test Loop
 A “while-loop” is also characterized as an
entry-test loop (like the for-loop). That is,
a condition about whether the loop
should continue is tested before actually
doing the work of the loop.
 A “do-while-loop” is an exit-test loop.
That is, the work of the loop is done
before the condition is tested about
whether the loop should continue.
Syntax of while-loop
while (booleanExpression)
{
//loop body
}
 Essentially, keep looping until the
condition is false.
Syntax of do-while-loop
Do {
//loop body
} while (booleanExpression);
 Essentially, do it once and then keep
looping until the condition is false.
The equals method
 The == operator does not always give us
the desired results when comparing two
objects (non-primitives).
 We need to use the equals method to
obtain information about object equality.
 All classes inherit this method from
java.lang.Object, but need to override it
to perform as appropriate.
The toString method
 Another method inherited from
java.lang.Object that should be
overridden to perform appropriately for
each object.
 This method gives a String
representation of an object that can be
printed out to the console using
System.out.println statements.