Java Array of Objects

What is the Java Programming Language?

If you are delving into the world of coding you will likely spend some time learning about the programming language Java.

Released in 1995 by Sun Microsystems, this programming language is very popular for coders for a variety of reasons. Java allows programmers to write using standard English, unlike other programming languages that require programmers to code in numbers. Java was produced to allow users on the Internet to interact with sites, and now it is used both on and off of the Internet, for instance, with mobile apps.

Arrays in Java

Writing programs using Java requires training and studying. This course covers the basics of programming with Java, which can get you on your way to programming in Java. In this article, though, we will talk a little about Java arrays and Java arrays of objects: what they are, how to set them up, and what they can do.

One side note before we begin: Arrays, in Java, are objects. They are dynamic. They can be assigned variables.

Also, the elements inside an array are objects.

To avoid confusion, in this article we will cover creating an array of objects using multiple variables inside the element.

To begin, you must first understand what an array is and how it is used in Java.

What is an Array in the Java Programming Language?

When developing programs in the Java programming language, an array stores values of the same type. Many people imagine an array as a type of container that can hold something.

Let’s think of a visual. Imagine an egg carton that holds one dozen eggs. Each of the twelve divots inside the egg carton is a storage unit. Each divot, or unit, can hold something of value (a coin, a piece of jewelry, a small cookie.)

This egg carton is your array.

Now, imagine that each divot has been numbered. Instead of starting at one, though, you begin numbering at zero.

All arrays in Java begin with the number zero.

Let’s Look at Another Example

With this visual in mind, let’s look at another example that might be more related to computer programming and that way of thinking.

Since we consider an array to be much like a container that holds a variety of variables of the same type, we can imagine the array to be like a spreadsheet, or a table. This table of ours contains two columns.  The first column contains the number. For the purpose of an array, that number is known as ‘index’. Again, all arrays begin at the number zero, so the first row, first column will be assigned the number zero, and as you move down the column you will number them in order.

The second column of the table contains a variable. Let’s use the months of the year as our variable in the example below. Next to the zero column we will write January, and we will go down the second column naming our variable, the months of the year, in order.

When you first begin to create the array you must define its length. After you define the length, this length cannot be changed. For our purposes, let’s define the length as five. Will this array contain all months of the year? No.

Since arrays begin at zero, the visual spreadsheet created would look similar to this.

Elements of the Same Type

Each item inside the array is called an element. Elements are objects. However, they can be numbers. They might be a type (type of car, age of students taking a particular class). Prior to developing the array, you must name the type of variable that will be used. (More on that here.)

Back to our example. Remembering  the index begins at zero,  when we refer to January we are referring to zero, not one, even though January is the first month.

Arrays may be filled with different items, but the programmer must name and create the elements that fill the array, and these elements must be of the same type.

Java: Array of Objects

Understanding arrays in Java is the first step. The above gave you a basic idea of what an array is when programming in Java. But what is an array of objects?

A Java array of objects can contain a number of variables. To begin the variable must be declared, as must the length, because this is, of course, the basic step in using arrays.

Let’s consider another example from those above that looks at a subject that can a variety of variables. Let’s create an array of objects that references a classroom of students. We can assign a variety of variables to these students. We can assign their age. We can assign their major. We can assign their homework and project averages.

We are now constructing an array of objects that centers around students. A variety of variables are being considered for each student.

Arrays of objects will contain a variety of properties. Think about it: One student might be 18 majoring in Philosophy with a final grade of C, while the next student might be 25 majoring in Education with a final grade of A. Once the array of objects (in this example, the objects are the students) has been created you can go on to sort the array of objects. This is handy when you want to reference one particular aspect of the array of objects.

The for loop or foreach loop can be used when processing a Java array of objects.

For More Information

Java programming is a fun and exciting way to create dynamic applications. Spend some time learning the basics of Java, and then venture into the more advanced coursework to learn about Java Applets and web applications.