The preceding section showed graphically the primary algorithms used for arrays. Now we’ll see how to write programs to carry out these algorithms, but we first want to cover a few of the fundamentals of arrays in Java. If you’re a Java expert, you can skip ahead to the next section, but even C and C++ programmers should stick around. Arrays in Java use syntax similar to that in C and C++ (and not that different from other languages), but there are nevertheless some unique aspects to the Java approach. Classes LowArray and LowArrayApp In lowArray.java, we essentially wrap the class LowArray around an ordinary Java array. The array is hidden from the outside world inside the class; it’s private, so only LowArray class methods can access it. There are three LowArray methods: setElem () and getElem(), which insert and retrieve an element, respectively; and a constructor, which creates an empty array of a specified size. Another class, LowArrayApp, creates an object of the LowArray class and uses it to store and manipulate data. Think of LowArray as a tool and LowArrayApp as a user of the tool. We’ve divided the program into two classes with clearly defined roles. This is a valuable first step in making a program object oriented. A class used to store data objects, as is LowArray in the lowArray.java program, is sometimes called a container class. Typically, a container class not only stores the data but also provides methods for accessing the data and perhaps also sorting it and performing other complex actions on it. Class Interfaces We’ve seen how a program can be divided into separate classes. How do these classes interact with each other? Communication between classes and the division of responsibility between them are important aspects of object-oriented programming.
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