chapter 5

Chapter 6: Using Methods, Classes, and Objects

Objectives

  • Creating Methods: Learn to create methods with no parameters, a single parameter, and multiple parameters.

  • Return Values: Understand how to create methods that return values.

  • Class Concepts: Learn about class concepts and how to create a class.

  • Instance Methods: Create instance methods within a class.

  • Object Declaration: Declare objects and utilize their methods.

  • Organizing Classes: Understand the organization of classes and their constructors.

  • Classes as Data Types: Recognize that classes are data types in Java.

Creating Methods

General Information

  • Method Definition: A method is a program module that contains a series of statements to perform a task.

  • Calling Methods: A method can be invoked (called) from another method.

  • Parameters and Arguments: Methods can take parameters, which are specified in the method declaration.

Method Structure

  • Method Header: Contains:

    • Access modifiers (optional)

    • Return type

    • Method name

    • Parameter list (optional)

  • Method Body: Enclosed in curly braces

    • Implementation of the method occurs here.

    • Methods without a body are called stubs.

Types of Parameters

Zero, One, Multiple Parameters

  • Zero Parameters: Methods defined without any parameters.

  • Single Parameter: Takes one argument for processing.

  • Multiple Parameters: Can accept multiple arguments, separated by commas.

Parameter Declaration Example
public static void methodName(int param1, String param2) {
    // method body
}

Method Return Values

  • Return Type: Can be any Java type; void indicates no return.

  • Return Statement: Used to return a value to the calling method.

  • Unreachable Statements: Occur after a return statement and cause compiler errors.

Calling a Method

  • Methods can call other methods which increases modularity and reusability.

  • Example:

public static double methodA(double amount) {
    // calculation
    return result;
}

Class Concepts

Defining Classes

  • Class Structure: A class definition includes a name, data fields, and methods.

    • Header defines access level and name.

    • Methods identify behavior of objects.

Instance Variables

  • Instance Variables: Hold data specific to an instance of a class.

  • Access Modifiers: Control visibility (public, private).

Using Constructors

  • Constructor Purpose: A special method to create and initialize objects.

  • Default Constructor: Automatically created if no constructors are defined; initializes fields with default values.

  • Custom Constructor: Must match the class name and can initialize with specific values.

Data Hiding and Encapsulation

  • Encapsulation: Hides the internal state of an object and requires all interaction to be performed through methods.

  • Access Methods:

    • Setters (Mutators) to change data.

    • Getters (Accessors) to read data.

Organizing Classes

  • Organizing data fields and methods logically improves readability. Methods often listed after data fields.

Summary

  • Methods: Are foundational in structuring Java programs for reusability and simplicity.

  • Classes: Serve as blueprints for objects that encapsulate data and behavior.

  • Constructors: Provide initial values for object attributes and are crucial for instantiation.