Of course, our classes are not very useful at this point because they don’t include any attributes or methods. Including attributes in a class is one of the simplest uses of classes, so let’s start there.

Person UML Diagram Person UML Diagram

Adding Attributes

To add an attribute to a class, we can simply declare a variable inside of our class declaration:

public class Person{
    String lastName;
    String firstName;
    int age;

That’s really all there is to it! We can also add default values to these attributes by assigning a value to the variable in the same line as the declaration:

public class Person{
    String lastName = "Person";
    String firstName = "Test";
    int age = 25;

However, it is very important to note that we cannot declare an attribute and then set the default value on a separate line. So, code such as this is not allowed:

Finally, we can add either the public keyword to the beginning of each of these attributes to make them available to code outside of this class, or the private keyword to prevent other code from accessing those attributes directly. We denote this by adding a + in front of the attribute in our UML diagram for public attributes, and a - for private attributes. In the diagram above, each attribute is private, so we’ll do that in our code:

public class Person{
    private String lastName;
    private String firstName ;
    private int age;