Job Ready Java

Lesson 15Creating Classes and Types

In this lesson, we'll look at how we define and create new types in Java and what comprises these new types.

LEARNING OBJECTIVES

By the end of this lesson, you will be able to:

• Create new types
• Differentiate between classes and objects
• Explain the use of accessors and mutators (or getters and setters)
• Use the dot operator to access object public properties or methods
• Use the this keyword
• Instantiate an object
• Invoke a method
• Relate constructors to methods
• Apply the static keyword to methods and constants

CREATING NEW TYPES

Every time we define a new class in Java, we are defining a new type. As discussed earlier in the course, there are two categories of data types in Java: primitive types and reference types. New classes fall into the latter category.

Types (classes) in Java simply consist of fields (or properties) and behaviors (or methods). Fields and behaviors are sometimes referred to as members. You have already used several user-defined types, including Scanner and String.

Listing 15.1 presents a new class called Dog. We could also say that Listing 15.1 is presenting a new type called Dog!

LISTING 15.1

A New Class/Type Called Dog

public class Dog {
 
    private String name;
    private double weight;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public double getWeight() {
        return weight;
    }
    
    public void setWeight(double weight) {
        this.weight = weight;
    }
    
 public ...