Java Reference
In-Depth Information
Chapter 3
Loops and Logic
WHAT YOU WILL LEARN IN THIS CHAPTER:
• How you compare data values
• How you can define logical expressions
• How you can use logical expressions to alter the sequence in which program statements are ex-
ecuted
• How you can select different expressions depending on the value of a logical expression
• How to choose between options in a fixed set of alternatives
• How long your variables last
• How you can repeat a block of code a given number of times
• How you can repeat a block of code as long as a given logical expression is true
• How you can break out of loops and statement blocks
• What assertions are and how you use them
In this chapter you look at how you make decisions and choices in your Java programs. You also learn how
to make your programs repeat a set of actions until a specific condition is met.
All your programs of any consequence will use at least some, and often most, of the language capabilities
and programming techniques I cover in this chapter, so make sure you have a good grasp of them.
But first, how do you make decisions in code and so affect the way the program runs?
MAKING DECISIONS
Making choices will be a fundamental element in all your programs. You need to be able to make decisions
such as, “If the user wants to enter more data, then read another value from the keyboard,” or, “If the bank
balance is large, buy the car with the go-faster stripes, else renew the monthly bus ticket.” Whatever decision
you want to make, in programming terms it requires the ability to make comparisons between variables, con-
stants, and the values of expressions and then execute one group of statements or another, depending on the
result of a given comparison. Thus, the first step to understanding how you make decisions in a program is to
look at how you make comparisons.
Making Comparisons
