Java Programming Concepts

Questions and Answers

What is created from classes in Java API?

Functions

Objects (correct)

Variables

Packages

How do you create a new Random object in Java?

Random rand = new Random();

Which of the following are important while working with objects? (Select all that apply)

Access Specifier

The object itself (correct)

Method Overloading

Reference variable (correct)

The new operator in Java is used to create an object and its memory address is assigned to a variable.

True Signup and view all the answers

What are the fields of the Rectangle class?

Length and Width Signup and view all the answers

The UML class diagram includes a class name, fields, and _____.

methods Signup and view all the answers

What is the file name convention for the Rectangle class in Java?

Rectangle.java Signup and view all the answers

What does a private access specifier mean?

The member can only be accessed from methods within the same class. Signup and view all the answers

What is the purpose of the setLength method?

To store a value in the length field. Signup and view all the answers

In Java, the void keyword indicates that a method _____.

returns no data Signup and view all the answers

What is the role of the rectangle variable in LengthDemo.java?

It references a Rectangle object. Signup and view all the answers

Study Notes

Java Classes and Objects

Classes in Java API serve as blueprints for creating objects. For example, a Scanner object is an instance of the Scanner class from the Java API.

Object Creation Examples

A primitive variable is declared as follows: int wholeNumber;
An object is instantiated using Random Rand = new Random();.

Components for Working with Objects

Two essential elements:
- The object itself, which must be created in memory.
- A reference variable that points to this object, enabling interaction with it (e.g., Random rand = new Random();).

Understanding Object Instantiation

The expression Random Rand declares a reference variable rand for a Random object.
new Random(); utilizes the new operator to create a Random object, returning its memory address.
The = operator assigns the returned address to the rand variable, allowing it to reference the Random object.

Class Structure Example

Define a Rectangle class with properties for length and width, alongside methods like setLength, setWidth, getLength, getWidth, and getArea for rectangle manipulation.

UML Overview

UML diagram structure:
- Line 1: Class name
- Line 2: Listed fields of the object
- Line 3: Methods defined in the class

Code Implementation of a Class

A simple class file should be named Rectangle.java with the declaration public class Rectangle.

Access Specifiers Explained

private: Restricts access to class members only within the same class.
public: Allows access to class members from outside the class.

Implementation of `setLength` Method

The setLength method enables external code to store a value in the length field of a Rectangle object, shown in the provided method body.

Method Definitions

void: Indicates the method returns no value.
setLength(double len): A method that accepts a double parameter to set the length of the Rectangle.
Instance methods operate on the class instances, lacking the static keyword.

Instance of a Class

Each object created from a class is considered an instance, with method bodies typically manipulating instance data, like setting the length field.

LengthDemo Example

The LengthDemo class illustrates object creation and method invocation:
- rectangle box = new Rectangle(); creates an instance and associates it with variable box.
- The system outputs the invocation of setLength(10.0).

Breakdown of `LengthDemo.java` Statements

Rectangle box = new Rectangle();: Declares a variable box of the Rectangle type, functioning as a reference variable that holds the memory address of the Rectangle object.
Upon calling new Rectangle(), an object is created and the box variable references this new instance.

Description

This quiz covers essential concepts related to Java programming, including classes and object creation. Through flashcards, you'll learn about the Java API and how to effectively declare and utilize objects in your programs. Brush up on your Java knowledge and test your understanding of object-oriented programming principles.