Module 1: Classes, Objects, and Access

Learning Objectives

Define instance variables to store the internal state of an object
Implement a class with multiple constructors to allow optional constructor arguments
Explain the relationship between a class and an object
Implement code to instantiate an object by calling a constructor with and without parameters
Declare variables of the correct types to store referenced objects
Explain the scope of visibility of a class's public and private member variables
Implement code to call an instance method and use its returned value
Implement code to call an instance method that has a void return type
Recall that calling a method executes the statements in the method before continuing
Define the behavior of an object through a method written in the class
Implement an instance method that reads the value of one of its class's instance variables
Implement an instance method that modifies the value of one of its class's instance variables
Implement an instance method with a reference to the current object using the keyword, "this"
Explain the scope of visibility of a local variable declared at the top of a method
Explain the scope of visibility of a local variable declared within a code block
Explain the scope of visibility of a method parameter variable

Key Concepts Explained

Classes are templates for creating objects. They define the structure and behavior that the objects will have.

Instance Variables

Instance variables store the state of an object. Each object created from a class has its own copy of these variables.

public class Person {
    // Instance variables
    private String name;
    private int age;
}

Constructors

Constructors initialize objects when they are created. You can have multiple constructors to provide different ways to create objects.

public class Person {
    private String name;
    private int age;
    
    // Default constructor
    public Person() {
        this.name = "Unknown";
        this.age = 0;
    }
    
    // Parameterized constructor
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

Access Modifiers

Access modifiers control the visibility of class members:

public: Accessible from any class
private: Accessible only within the declaring class
protected: Accessible within the package and subclasses
default: Accessible only within the package

Methods

Methods define the behavior of objects. They can access and modify instance variables.

public class Person {
    private String name;
    
    // Getter method - reads an instance variable
    public String getName() {
        return this.name;
    }
    
    // Setter method - modifies an instance variable
    public void setName(String name) {
        this.name = name;
    }
}

Module 1: Classes, Objects, and Access

Module Overview

Learning Objectives

Key Concepts Explained

Instance Variables

Constructors

Access Modifiers

Methods

Key Topics

Classes

Objects

Access Modifiers

Guided Practice

Resources:

Additional Resources

Next Steps