Java Fundamentals: Objects, Methods, and Data Types

Object-Oriented Programming (OOP)

A programming paradigm that uses 'objects' to represent data and methods to work with that data.

Class

The blueprint or template that defines the properties and methods of an object.

Object (Instance)

A specific realization of a class that takes up memory in the heap.

new keyword

Used in Java to create a new instance of a class.

Constructor

A method used to initialize an object.

Primitive Data Types

Basic data types in Java, such as int, double, and boolean.

int

A primitive data type used to represent integers.

double

A primitive data type used for floating-point numbers.

boolean

A primitive data type that can hold only true or false values.

Reference Data Types

Data types that hold references to objects rather than actual values.

Wrapper Classes

Classes that allow primitive data types to be treated as objects.

Autoboxing

The automatic conversion of a primitive type into its corresponding wrapper class.

Unboxing

The automatic conversion of a wrapper class object into its corresponding primitive type.

Method

A block of code that performs a specific task and can be called upon.

Void Method

A method that does not return a value.

Return Method

A method that returns a value after execution.

Method Overloading

Defining multiple methods with the same name but different parameter lists.

String

A sequence of characters that is a reference type in Java.

Immutable

A property of an object that cannot be modified after it is created.

Concatenation

The operation of joining two strings together using the + operator.

length()

A method that returns the number of characters in a string.

substring(int from, int to)

A method that returns a substring from index 'from' to index 'to'.

indexOf(String str)

A method that returns the index of the first occurrence of a specified string within another string.

equals(Object other)

A method that checks if two strings have the same content.

Math Class

A class in Java that contains static methods for performing mathematical operations.

Math.abs(x)

Returns the absolute value of x.

Math.pow(base, exponent)

Returns the value of base raised to the power of exponent.

Math.sqrt(x)

Returns the square root of x.

Math.random()

Returns a random double value between 0.0 and 1.0.

Generating Random Integers Formula

(int)(Math.random() * range) + min, where range is (max - min + 1).

Integer Division

The division of two integers that truncates any decimal part.

String Comparison

The act of comparing two string values using .equals() instead of ==.

NullPointerException

Runtime error that occurs when trying to access an object that is null.

Casting in Java

The conversion of one data type into another.

Reference Variable

A variable that holds the memory address of an object.

Rectangle

A class example used to illustrate how to create objects in Java.

Scanner

A class in Java used for reading input from various sources.

Random

A class in Java used for generating random numbers.

String Methods

Functions available for string manipulation in Java.

Memory Address

The location in memory where an object is stored.

State

The data contained within an object.

Behavior

The methods that define what operations can be performed on an object.

Logical Hierarchy

An organizational structure that represents relationships in class and object definitions.

Assignment Operator ( = )

Used to assign values to variables.

Parameters

The values that are passed to a method when it is called.

Index Out of Bounds

Error that occurs when accessing an index that is outside the valid range of a string.

Compilation Error

Error that occurs during the compilation of code due to syntax or type issues.

Immutable String

A string that cannot be altered once it is created.

Comparative Method

A method that compares objects based on predefined criteria.