Java control structures - Objects First with Java: A Practical Introduction Using BlueJ - page 510

APPENDIX
D

Java control structures

D.1 Control structures

Control structures affect the order in which statements are executed. There are two main catego-
ries: selection statements and loops .

A selection statement provides a decision point at which a choice is made to follow one route
through the body of a method or constructor rather than another route. An if-else statement in-
volves a decision between two different sets of statements, whereas a switch statement allows
the selection of a single option from among several.

Loops offer the option to repeat statements, either a definite or an indefinite number of times.
The former is typified by the for-each loop and for loop , while the latter is typified by the while
loop and do loop .

In practice, it should be borne in mind that exceptions to the above characterizations are quite
common. For instance, an if-else statement can be used to select from among several alternative
sets of statements if the else part contains a nested if-else statement, and a for loop can be used
to loop an indefinite number of times.

D.2 Selection statements

D.2.1 if-else
The if-else statement has two main forms, both of which are controlled by the evaluation of a
boolean expression:

if ( expression ) { if ( expression ) {

statements statements

} }
else {
statements

}

In the first form, the value of the boolean expression is used to decide whether or not to execute
the statements. In the second form, the expression is used to choose between two alternative
sets of statements, only one of which will be executed.