Java and OOP Fundamentals

• These notes cover various fundamental concepts of Java and object-oriented programming (OOP).

Abstract Classes in Java

• The abstract keyword is used to create an abstract class in Java.
• Abstract classes cannot be instantiated directly.

IF Statement Conditions

• If the condition inside an IF statement is false, the code inside the ELSE block executes (if present).

Procedural Programming: Data and Functions

• In procedural programming, data and functions are separate and not directly related.

Two-Dimensional Arrays

• A two-dimensional array is a list of arrays.

Loop Execution

• while (false) { ... } will not execute at all because the condition is initially false.

Equality Operator

• The == operator is used to compare two values for equality in Java.

Superclass Synonym

• A superclass is also known as a parent class.

Double Data Type

• The double data type is used to store floating-point numbers with higher precision.

Java Methods

• In Java, methods must include a body and a declaration, but not necessarily a call to another method.

Instance Variables

• The non-static data components of a class are often referred to as instance variables of that class.

Java Code Result

• For the code boolean result = (10 > 5) && (5 > 3), the result will be true.

OOP Principles

• Iteration is not a main principle of OOP; the main principles are Inheritance, Encapsulation, and Polymorphism.

Method Call

• If a method is declared as public static void showResults(double d, int i), a correct method call would be showResults(4, 99.7);.

Floating-Point Variable Declaration

• The correct syntax to declare a floating-point variable in Java is float value = 3.14F;.

Interface Implementation

• The implements keyword is used to use an interface from a class.

Data Encapsulation

• The concept of allowing a class's private data to be changed only by a class's own methods is known as information hiding.

Boolean Data Type

• Java's boolean data type can store only true or false.

Storing Height

• float data type is best suited for storing a person's height in meters, due to its ability to store decimal values.

Key Concepts in OOP

• Reflection is not a key concept in OOP.

Nested If-Else Statements

• Nested if statements allow multiple conditions to be evaluated sequentially.

Array Storage

• If you try to store 1000 elements in an array declared as new int[100], a runtime exception will occur.

Java Code Execution

• Given the code int x = 4; x -= 2;, the value of x after execution will be 2.

Array Initialization

• The correct way to initialize a 1-dimensional array with values 10, 20, and 30 is int[] arr = {10, 20, 30};.

Interfaces in OOP

• The main advantage of using interfaces in OOP is that it allows multiple inheritance in a structured way.

Switch Statement Conditions

• switch(5.5) is not a valid condition for a switch statement because switch statements do not allow doubles.

Method Return Types

• If a method is declared as public static int getVal(double sum), the last legally coded line could be return 77;.

Object Interaction

• You send messages or information to an object through its methods.

Encapsulation Purpose

• The purpose of encapsulation in OOP is to hide implementation details from users and provide a public interface.

Function of Interfaces

• The function of using interfaces is to specify the behavior of a class.

Function of Abstract Class

• The function of an abstract class is to be a restricted class that cannot be used to create objects.

Loop Execution and Infinite Loops

• The loop while (1==1) { System.out.println("Hello"); } will execute infinite times.

Incorrect Java Statement

• int x = 5.5; is an incorrect Java statement because you can't assign a double value 5.5 to an integer variable x.

Default Value of Uninitialized Array

• The default value of an uninitialized int two-dimensional array in Java is 0.

Initializing a 2D Array

• To initialize a two-dimensional integer array with values {{10, 9}, {5, 3}}, the correct syntax is int[][] arr = {{10, 9}, {5, 3}};.

Exiting a Loop

• The break keyword is used to exit a loop immediately.

Unary Operator

• ++ is an example of a unary operator in Java.

Fundamental Principles of OOP

• Compilation is not a fundamental principle of Object-Oriented Programming.

Functional Programming

• Haskell is closer to functional programming than OOP.

Abstraction in OOP

• Abstraction in OOP is used for hiding implementation details and showing only the relevant features to users.

Loop Guaranteeing One Execution

• The do-while loop structure guarantees that the loop body will execute at least once.

Initializing Integer Arrays

• To initialize an integer array of size 5 with all elements set to zero, you can use int[] arr = new int[5];.

Two Dimensional Arrays in Java

• In Java, a two-dimensional array is a list of arrays where rows can have different lengths.

OOP vs. Procedural Programming

• OOP uses classes and objects, while procedural programming uses function-based modules.

Do-While Loop

• In a do-while loop, the loop executes at least once even if the condition is false.

Calling Methods

• Given a method declared as public static void aMethod(char code), a correct call to it is aMethod('Q');.

Java Expression

• The result of the Java expression 3 + 2 * 4 is 11.

Class Body

• The body of a class is always written between curly braces.

Default Array Values

• The default value of an integer array element in Java is 0.

OOP Constructors

• If a class in OOP does not have a constructor, the compiler automatically provides a default constructor.

Java Code Result

• Given the code int x = 7; x += -3; System.out.println(x);, the result will be 4.