What is a data structure anyway? We have been using data stuctures of some type in all our programs so far. Data are information stored in the computer's memory. A byte is a structure of 8 bits. A float is a structure of usually 4 bytes. We can say that data in its purest unstuctured form is a bit. It is capable of only being 1 or 0 , "on" or "off". When I use the relationship between different datum to signivfy something then I then I must structure the data as i choose. The second bit of a byte means 0 or 2 because it is in the second place. That is what is meant by structured data. The different bytes of a double have different meanings based on their location. These are very simple data structures and not what is usually meant by the term "data structures"

The next most complex data structure is the class. In a class we group attributes together in one package. This gives form to our data. Moreover, the definition of the class may impart meaning to a particular piece of data. For example, the attribute "name" of type String in class dog would mean the name of the dog, but the attribute "name" in a class called student would mean the name of the student. Here we can see that the location of data can give it significance. But this is also not the type of data structure we will be focusing on.

In this course, we will deal with how we group primitive data types together and how we group classes together. We have already grouped primitive data types together when we made arrays. An array of integers is a data stucture in its more common sense. An array gives some structure to a set of data. This enables us to sort the data or search the data. This would not be possible if the data were stored in variables having no relationship to each other. If I made 10 separate variable named something like "grade1", "grade2", I could not sort them because there would be no reference point by which to sort them. However if I make an array called "grades" and use it to store the grades, then I can sort the grades. We can also make arrays of user-defined classes. In the example program kennel.java we created an array of dogs. So far the array is the only data structure we have learned to create.

© Nachum Danzig December 2003