Programming and Problem Solving with Java

(^500) | One-Dimensional Arrays

Arrays of User-Defined Objects

In the last example, the components of the array were strings. Now let’s look at an array of

user-defined objects. We have used a Nameclass in several Case Studies. The following code

declares and instantiates an array of elements of the class Name:

Name[] friends = new Name[10];

The following table shows the types involved and indicates how to access the various

components:

Expression Class/Type

friends Reference to an array

friends[0] Reference to a Nameobject

friends[0].knowFirst() Reference to a string

friends[0].knowLast() Reference to a string

friends[0].knowMiddle() Reference to a string

friends[0].knowFirst().charAt(1) A character

10.6 Arrays and Methods

The only observer method provided for arrays is component access, which has its own spe-

cial syntax: the array variable’s name, followed by an index enclosed in brackets. The index

specifies which component to access.

When we use an array as a field in a class, however, we may need to pass an array vari-

able as an argument to a method or pass a component of an array to a method. Recall that

a copy of each argument is sent to the method. Because an array, like a class, is a reference

type, the method receives the address indicating where the object is stored.

Suppose we define a publicclass method (say, in the class Accounting) that takes the ar-

ray as an argument and returns the sum of the components in the array:

public static doublesumSales(double[] data)

{

doublesum = 0.0;

for (int index = 0; index < data.length; index++)

sum = sum + data[index];

returnsum;

}

The following code uses the methodsumSalesto sum the week’s gourmet hamburger sales:

outFile.print("This week's sales of gourmet hamburgers: ");

outFile.println(Accounting.sumSales(gourmetBurgers));

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