Java Reference
In-Depth Information
Chapter 4
Arrays and Strings
WHAT YOU WILL LEARN IN THIS CHAPTER
• What arrays are and how you declare and initialize them
• How you access individual elements of an array
• How you can use individual elements of an array
• How to declare arrays of arrays
• How you can create arrays of arrays with different lengths
• How to create String objects
• How to create and use arrays of String objects
• What operations are available for String objects
• What StringBuffer objects are and how they relate to operations on String objects
• What operations are available for StringBuffer objects
In this chapter you start to use Java objects. You are first introduced to arrays, which enable you to deal
with a number of variables of the same type through a single variable name, and then you look at how to
handle character strings. Some of what I discuss in this chapter relates to objects, and as I have not yet covered
in detail how you define a class (which is an object type definition), I have to skate over some aspects of how
objects work, but all is revealed in Chapter 5.
ARRAYS
With the basic built-in Java data types that you've seen in the previous chapters, each identifier corresponds
to a single variable. But when you want to handle sets of values of the same type — the first 1,000 primes,
for example — you really don't want to have to name them individually. What you need is an
array
.
You should first have a rough idea of what an array is and how it works. An array is an object that is a
named set of variables of the same type. Each variable in the array is called an
array element
. To reference a
particular element in an array, you use the array name combined with an integer value of type
int
, called an
index
. You put the index between square brackets following the array name; for example,
data[99]
refers to
the element in the
data
array corresponding to the index value 99. The index for an array element is the offset
of that particular element from the beginning of the array. The first element has an index of 0, the second has
an index of 1, the third an index of 2, and so on. Thus,
data[99]
refers to the hundredth element in the
data
array. The index value does not need to be an integer literal. It can be any expression that results in a value of
