Java Software Solutions Chapter 3

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Questions and Answers

What is the process of creating an object in Java called?

Declaration

Instantiation (correct)

Construction

Initialization

An object reference variable contains the actual object it points to.

False

How can you invoke a method on an object?

Using the dot operator.

The act of ___ takes a copy of a value and stores it in a variable.

assignment Signup and view all the answers

Which of the following types of class features does Chapter 3 NOT focus on?

Exception Handling Signup and view all the answers

What is garbage collection in Java?

The automatic process of reclaiming memory from objects that are no longer referenced. Signup and view all the answers

Aliases are multiple references that can refer to the same object.

True Signup and view all the answers

Which operator is used in Java to create an object?

new Signup and view all the answers

What happens when an object no longer has any valid references?

It is considered garbage and can be collected by the garbage collector. Signup and view all the answers

Which of the following is NOT a focus of Chapter 4?

Data structures Signup and view all the answers

What is encapsulation?

The bundling of data and methods that operate on that data within a class. Signup and view all the answers

What does the roll method do in the Die class?

It sets faceValue to a random number between one and six. Signup and view all the answers

An object has only state but no behavior.

False Signup and view all the answers

The class that contains the main method is just the ______ of a program.

starting point Signup and view all the answers

What is the significance of the Die class?

It serves as a blueprint for creating die objects that model the state and behavior of a die. Signup and view all the answers

What is the purpose of the setFaceValue method?

It sets the face value of the die to a specified number. Signup and view all the answers

The state of an object is defined by its ______.

data Signup and view all the answers

Match the following concepts with their definitions:

Class = A blueprint for creating objects Object = An instance of a class Method = A function defined within a class Encapsulation = The bundling of data and methods within a class Signup and view all the answers

Study Notes

Using Classes and Objects in Java

Object-oriented programming in Java enables the creation of complex programs through predefined classes and objects.
Focus areas include object creation, references, the String class, Java API, Random and Math classes, output formatting, and JavaFX graphics.

Creating Objects

Variables can hold primitive values or references to objects, allowing for flexible data handling.
Object reference variables are declared using class names, e.g., String title;, but do not create an object immediately.
Objects are instantiated using the new operator, e.g., title = new String("Java Software Solutions");, which invokes a constructor to set up the object.

Invoking Methods

Once an object is instantiated, its methods can be accessed using the dot operator, e.g., numChars = title.length();.
Method invocations represent requests for the object to perform specific functions or return values.

References vs. Primitive Variables

Primitive variables contain direct values, while object variables store memory addresses pointing to the object.
Object references can be visually represented as pointers to memory locations, differentiating them from simple value storage.

Assignment

Assigning values for primitive types copies the direct value, creating a separate instance.
For object references, assignment copies the memory address, leading to shared access between variables, potentially creating aliases.

Aliases

Multiple references pointing to the same object form aliases, which can facilitate data manipulation but require careful management to avoid unintended changes across the aliases.
Modifications through one reference affect all aliases since they point to the same object in memory.

Garbage Collection

When objects lack valid references, they become inaccessible and are termed garbage.
Java automatically performs garbage collection to reclaim memory space occupied by these unreferenced objects, unlike some languages where programmers must manage memory manually.

The String Class

The String class is fundamental in Java, optimizing string handling without requiring explicit instantiation with new for common string operations.

Writing Classes in Java

Focus of Chapter 4: writing user-defined classes, covering aspects like definitions, instance data, encapsulation, method declaration, parameter passing, and constructors.
Key components: arcs, images, events, event handlers, buttons, and text fields.

Understanding Classes

Programs previously utilized predefined classes from the Java API; now, the focus is on designing and writing custom classes.
True object-oriented programming involves creating classes that encapsulate objects with specific characteristics and functionalities.

Object Model

Objects consist of state (attributes) and behavior (methods).
Example of a class: A six-sided die represented by a class called Die, with states defined by the showing face and behavior defined by rolling.

Class Composition

Classes contain data declarations and method declarations.
Example data declarations in a class: int size, weight;, char category;.
Methods define behavior, e.g., a method in the Die class to set the face value to a random number between 1 and 6.

Reusability and Versatility

Classes should be designed to be versatile and reusable across different programs.
Not all class operations will be used in every instance; they should remain effective for various applications.

Sample Class Implementation

Sample Java code demonstrates user-defined class creation through RollingDice, which includes:
- Instantiating two Die objects.
- Rolling the dice multiple times.
- Using setFaceValue and getFaceValue methods to manipulate and retrieve the current state.

Example Program Functionality

The RollingDice program rolls two dice and outputs their values and sums.
Demonstrates encapsulation by manipulating internal state through public methods.

Output Example

Example output demonstrates the functionality where:
- die1.roll(); might result in outputs like Die One: 5, Die Two: 2.
- Adjusting face values and recalculating sums illustrate method usage and state manipulation.

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Description

Dive into Chapter 3 of 'Java Software Solutions', where the concepts of classes and objects are explored. This chapter covers object creation, object references, and the String class, essential for developing engaging programs. Learn how to leverage predefined classes to enhance your programming skills.