Java Full Course for Beginners

This course offers a comprehensive introduction to programming in Java, covering everything from tool installation to building algorithms. Designed for beginners, it simplifies complex concepts and provides hands-on guidance for writing professional-quality code. With insights drawn from two decades of experience and teaching millions worldwide, the instructor ensures learners gain a solid foundation in Java while preparing them for advanced features.

To build Java applications, download the JDK (Java Development Kit) from Oracle's website. The JDK includes essential tools like a compiler, reusable code libraries, and the Java Runtime Environment. After accepting the license agreement, install it using an easy installation wizard on your platform of choice—Linux, MacOS or Windows. Next is selecting a code editor; popular options include NetBeans, Eclipse or IntelliJ IDEA. For this tutorial series specifically recommends downloading free Community Edition version IDEA.

Understanding Functions in Java Functions are the smallest building blocks of a Java program, performing specific tasks like sending emails or converting measurements. They begin with specifying a return type (e.g., void for no value), followed by a descriptive name and optional parameters enclosed in parentheses. The function's code resides within curly braces, adhering to conventions such as placing the left brace on the same line as its definition.

Classes and Methods: Organizing Code in Java In Java, functions must belong to classes which act as containers organizing related methods—functions tied specifically to these classes. Every program requires at least one class containing the main method that serves as an entry point when executed. Classes use Pascal naming convention (uppercase first letters) while methods follow camel case (lowercase initial letter). Access modifiers like public determine visibility across other parts of programs.

Setting Up Your First Java Project Begin by opening IntelliJ IDEA and creating a new project. Select 'Java' as the language, ensure JDK is properly configured, and choose to create a command-line application for simplicity. Name your project (e.g., "Hello World") and set up its base package using reverse domain naming convention or any placeholder name of choice.

Understanding Java's Structure: Packages, Classes, Methods In the created project structure within IntelliJ IDEA, observe that files are organized into packages which group related classes together. The main class contains methods like 'main', marked static so it can be executed without an instance of the class. Statements in Java end with semicolons; comments start with double slashes for code explanation but do not execute.

Writing & Executing Your First Program Write your first program inside the main method using System.out.println("Hello World"); to print text on terminal output—textual data must always be enclosed in double quotes as strings represent sequences of characters in Java syntax conventions! Execute this via toolbar icons or shortcuts such Ctrl+R ensuring successful build results displaying expected outputs!

A detailed cheat sheet with summary notes is available for download, eliminating the need to memorize course content. The creator has aimed to provide a high-quality Java learning experience and encourages viewers to support by liking, sharing on social networks, subscribing, and enabling notifications for future updates.

How Java Code is Compiled and Executed When a Java program runs in IntelliJ, it undergoes two steps: compilation and execution. During compilation, the code transforms into platform-independent bytecode using the Java compiler from the JDK. This bytecode can run on any operating system with a compatible JVM (Java Virtual Machine), which translates it to native OS-specific code for execution. The portability of this architecture allows developers to write programs once and execute them across various platforms seamlessly.

Key Facts About Java's History and Usage Java was created by James Gosling in 1995 at Sun Microsystems, later acquired by Oracle in 2010; its name originates from coffee inspiration after being initially called Oak then Green. It offers four editions tailored for different applications: Standard Edition (core libraries), Enterprise Edition (large-scale systems), Micro Edition (mobile devices), and Card Edition (smart cards). With nearly 9 million developers globally, billions of devices like phones, TVs, Blu-ray players rely on it daily—making proficiency highly valuable as reflected by an average US salary exceeding $100K annually.

This course is the first of a four-part series designed to teach Java programming comprehensively. The initial part focuses on fundamentals, including types like strings and arrays, culminating in building a mortgage calculator project with data validation. It progresses into control flow statements for algorithm development and emphasizes clean coding techniques for writing maintainable code. Later sections cover debugging, packaging programs for deployment, object-oriented programming essential across applications, core Java APIs from its standard library, and advanced features such as streams and database integration.

This lesson covers the essentials of Java programming, including variables, constants, primitive and reference types. It explains type conversion (casting), working with numbers, strings, arrays, and user input handling. After mastering these concepts through attentive learning of the materials provided in this session, learners will apply their knowledge by creating a mortgage calculator project independently.

Variables are used to temporarily store data in a computer's memory. In Java, variables must be declared with a type (e.g., int for integers) and an identifier or name. The assignment operator (=) is used to assign an initial value, which is mandatory before reading the variable. Values can be updated later, but it's recommended to declare one variable per line for clarity. Additionally, values from one variable can be copied into another using simple assignments. Naming conventions like camelCase should be followed where the first word starts lowercase while subsequent words begin with uppercase letters.

Understanding Primitive Types in Java Java categorizes data types into primitive and non-primitive (reference) types. Primitive types store simple values, such as whole numbers with byte, short, int, long; decimal numbers with float or double; single characters using char; and boolean for true/false values. Each type has specific memory requirements: byte uses 1 byte while long requires 8 bytes to handle larger ranges of data.

Practical Usage of Variables in Java Choosing the right variable type optimizes memory usage—for example, storing age can use a smaller 'byte' instead of an 'int'. Large integers require declaring them as 'long', adding an uppercase L suffix to avoid errors since default numeric literals are treated as integers. Similarly for decimals stored in floats rather than doubles—adding F ensures correct interpretation by the compiler.

Understanding Reference Types in Java Reference types are used to store complex objects like data or mail messages, unlike primitive types which handle simple values such as numbers and characters. In Java, there are eight primitive types; all other variable classes and methods fall under reference types. Declaring a reference type involves using the 'new' operator to allocate memory for an object instance of a class template (e.g., Date). Unlike primitives where memory management is automatic, with references you explicitly create instances but rely on Java's runtime environment for cleanup.

Accessing Members of Objects vs Primitive Variables Objects created from classes have members accessible via the dot operator (e.g., methods like getTime), while primitives lack these features since they aren't objects. For example, calling age.dot yields no results because it's not an object but rather a basic value holder without additional functionality. Printing out variables differs too: strings require quotes whereas direct printing outputs their actual content—demonstrated by displaying date information directly through System.out.println().

Memory Independence in Primitive Types Primitive types store simple values directly in memory, making them independent of each other. When a primitive variable is assigned to another, the value itself is copied into a new memory location. Changes made to one variable do not affect the other because they occupy separate spaces in memory.

Shared References with Reference Types Reference types store addresses pointing to objects rather than actual object data. Assigning one reference type variable to another copies this address, meaning both variables point to the same object in memory. Consequently, changes made through either variable are reflected across both since they share access to the same underlying object.

Understanding Strings and Their Initialization in Java Strings in Java are sequences of characters, often represented as string literals. They can be stored in variables using the String class from the java.lang package, which is automatically imported into every program. While strings are reference types requiring instantiation with 'new', a shorthand allows direct assignment of string literals for simplicity. This approach makes working with strings more efficient while maintaining their nature as immutable objects.

Exploring Useful Methods for Manipulating Strings Java's String class offers various methods to manipulate text effectively. Concatenation combines strings using '+', while methods like startsWith(), endsWith(), length(), indexOf() check specific conditions or retrieve information about a string’s content and structure. Replace() substitutes parts of a string without altering its original value due to immutability; similarly, trim() removes unnecessary spaces at edges, and case conversion functions (toLowerCase/toUpperCase) adjust letter casing efficiently.

Escape sequences allow the inclusion of special characters like double quotes, backslashes, new lines, and tabs within strings. To include a double quote inside a string without causing errors, prefix it with a backslash (e.g., \"Marsh\"). Similarly, to represent file paths on Windows using backslashes (e.g., C:\Windows), each single backslash must be escaped by another one. The escape sequence \n adds new lines while \t inserts tabs into strings for better formatting. These four essential escape sequences are crucial for handling complex string manipulations effectively.

Understanding Arrays in Java Arrays in Java are used to store lists of items, such as numbers or messages. To create an array, square brackets are added after the data type and its size is specified using the 'new' operator. Individual elements can be accessed via their index starting from zero; however, accessing invalid indices results in exceptions that crash programs. By default, printing arrays shows memory addresses instead of contents unless formatted with methods like `toString` from the `Arrays` class.

Array Initialization and Manipulation Techniques Java allows initializing arrays directly with predefined values using curly braces for simplicity compared to older syntax involving explicit assignments. The length property provides a fixed count of elements since arrays cannot dynamically resize—collections should be used for flexible sizes instead. Sorting operations on unsorted numeric content within these structures utilize built-in utilities like `sort`, ensuring ordered arrangements efficiently without manual intervention.

Arrays in Java can store lists of objects and extend to multi-dimensional forms, such as two-dimensional arrays for matrices or three-dimensional arrays for cubes. To create a 2D array, additional square brackets are added on both sides with specified dimensions (e.g., 2 rows by 3 columns). Accessing elements requires specifying row and column indices; printing these structures uses the 'deepToString' method from the Arrays class instead of 'toString'. For initialization using curly braces syntax, each row is defined as an individual array within another array structure.

Variables can be changed throughout a program's lifetime, but constants are used when values must remain unchanged. For example, declaring 'pi' as 3.14 and marking it with the keyword 'final' ensures its value cannot be altered later on. This prevents errors like accidentally reassigning pi to another number, which would disrupt calculations such as finding the area of a circle. By convention, constant names use all capital letters (e.g., PI).

Arithmetic expressions in Java use operators like addition, subtraction, multiplication, division, and modulus. Division between integers results in an integer; to get a floating-point result, numbers must be cast as float or double. Increment and decrement operators can increase or decrease values by 1 using prefix or postfix notation with different outcomes when used on the right side of assignment operations. To increment by more than one value efficiently, compound assignment operators such as += are preferred over traditional methods.

In mathematical expressions, multiplication and division take precedence over addition and subtraction. For example, in the expression 10 + 3 × 2, the multiplication (3 × 2) is calculated first to give 6, which is then added to 10 resulting in a total of 16. To alter this order explicitly, parentheses can be used; for instance (10 + 3) × 2 evaluates the sum inside parentheses first (13), followed by multiplying it with 2 to yield 26. Parentheses always have the highest priority when determining operation sequence.

Understanding Implicit and Explicit Casting in Java Casting allows conversion between data types, either implicitly or explicitly. Implicit casting happens automatically when converting smaller to larger data types without losing information (e.g., short to int). For explicit casting, the programmer manually converts a value using syntax like '(int)', especially when precision loss is acceptable (e.g., double to int). However, incompatible types such as strings cannot be directly cast; instead, methods like 'Integer.parseInt()' are used for conversions.

Practical Applications of Type Conversion Type conversion is essential in applications where user input often comes as strings but needs numeric representation for calculations. Methods from wrapper classes like 'parseDouble()' handle these transformations effectively while ensuring compatibility with different number formats. Errors occur if inappropriate parsing methods are applied—like trying to parse floating-point numbers into integers—which highlights the importance of selecting suitable type-conversion techniques based on context.

Exploring Java's Math Class Methods Java's Math class, part of the java.lang package, provides essential methods for mathematical operations without requiring explicit import. Key functions include 'round' to convert floating-point numbers to whole numbers (overloaded for float and double), 'ceil' which returns the smallest integer greater than or equal to a number, and 'floor', yielding the largest integer less than or equal. The class also offers comparison tools like 'max' and 'min', determining larger or smaller values between two inputs respectively.

Generating Random Numbers with Precision in Java 'Random' generates a value between 0 and 1 as a double; multiplying it by an upper limit adjusts its range (e.g., 0-100). To eliminate decimal points from results, use either rounding methods ('Math.round') or casting techniques while ensuring proper parentheses placement around expressions. Incorrectly placed casts lead to unintended outcomes such as always returning zero due to truncation before multiplication.

Formatting Numbers as Currency and Percentages in Java In Java, the NumberFormat class from the text package is used to format numbers into currency or percentage representations. Since this class is abstract, it cannot be instantiated directly; instead, factory methods like getCurrencyInstance() and getPercentInstance() are utilized to create specialized instances for formatting. For example, calling these methods allows you to convert a number such as 1234567.891 into a formatted string with commas separating every three digits and two decimal places (e.g., $1,234,567.89) or transform 0.1 into "10%".

Efficient Code Practices: Method Chaining & Refactoring Variables To streamline code when using NumberFormat objects only once within a program context—like converting values directly without storing intermediate variables—you can apply method chaining by invoking multiple methods consecutively on an object instance returned inline via its respective call-chain logic rather than assigning temporary placeholders beforehand! Additionally leveraging IDE tools' refactor-renaming capabilities ensures consistent updates across all references seamlessly avoiding manual oversight errors during variable renames simplifying maintenance/debugging workflows significantly!

Reading User Input in Java To read user input in Java, the Scanner class from java.util package is used. By creating a scanner object and specifying System.in as the data source, various methods like nextByte(), nextLine(), or nextFloat() can be employed to capture different types of inputs such as bytes, strings, or floating-point numbers. Implicit type conversion allows combining byte variables with strings for output display.

Handling Strings and Trimming Whitespace The difference between using 'next' and 'nextLine' lies in how they handle tokens; 'next' reads one token at a time while 'nextLine' captures an entire line including spaces. To remove unwanted leading or trailing whitespace from string inputs captured via `Scanner`, the trim method is applied before storing it into variables. This ensures cleaner outputs regardless of extra spaces entered by users.

The project involves creating a mortgage calculator that asks users for three inputs: the loan principal, annual interest rate, and repayment period in years. Using these inputs, it calculates monthly payments using a specific formula. The formula requires converting the annual interest rate into a monthly one by dividing it by 100 (to get decimal form) and then by 12. Additionally, the number of total payments is calculated as years multiplied by 12 months per year. To compute powers needed in this calculation, use the Math class's power method.

Avoiding Magic Numbers and Meaningful Naming in Code The implementation of a mortgage calculator emphasizes the importance of avoiding magic numbers by using constants or final variables, such as 'monthsInYear' set to 12 and 'percent' set to 100. This practice ensures clarity for anyone reading the code, preventing confusion about arbitrary values like "12" representing months in a year. Additionally, meaningful variable names are used instead of cryptic abbreviations (e.g., "monthlyInterest" rather than "MI") to enhance readability.

Efficient Data Types and Input Validation Challenges Appropriate data types were chosen based on their requirements: integers for principal amounts up to two billion dollars; floats for small annual interest rates; bytes for periods capped at thirty years. The program calculates monthly payments with clear formulas but lacks input validation—issues arise when non-numeric or negative inputs cause crashes or improper behavior. Future improvements involve implementing conditional statements to handle invalid user entries effectively.

This section covers the fundamentals of variables and constants, explaining their roles in programming. It distinguishes between primitive types that store simple values and reference types that hold references to complex objects. Key concepts include implicit and explicit casting for type conversion as well as working with numbers, strings, arrays, and reading input from the terminal.

Control flow determines the execution sequence of a program. It begins with comparison operators to compare values, followed by logical operators like AND, OR, and NOT for applying real-world rules. Key control flow statements include conditional statements for decision-making and loops for repetitive tasks. Additionally, error handling is introduced through practical examples such as enhancing a mortgage calculator to manage invalid user inputs effectively.

Comparison operators are used to evaluate relationships between primitive values, producing boolean expressions that return true or false. The equality operator (==) checks if two variables have the same value, while the inequality operator (!=) determines if they differ. Additional operators include greater than (>), less than (<), and their inclusive counterparts (>= and <=). For example, comparing x = 1 with y = 2 using 'x <= y' evaluates to true because x is indeed less than or equal to y.

Combining Conditions with Logical AND and OR Operators Boolean expressions yield true or false values, but combining them can create more complex conditions. Using the logical AND operator (&&), both conditions must be true for the result to be true; otherwise, it’s false. For example, checking if a temperature is between 20 and 30 involves two comparisons joined by &&—if either fails, Java stops evaluating further as the overall condition cannot succeed. The logical OR operator (||) requires only one of its conditions to be true for an overall positive outcome; evaluation halts once any single condition proves valid.

Reversing Boolean Values with NOT Operator in Complex Rules The NOT operator (!) reverses boolean values and helps refine conditional logic when combined with other operators like AND or OR. In loan eligibility scenarios where applicants need high income or good credit without criminal records: first combine income/credit checks using || then negate a 'has criminal record' variable via ! before linking all criteria through &&. This ensures precise rule implementation while leveraging these versatile operators effectively in real-world applications.

Building Decision-Making Programs with If Statements in Java If statements are essential for creating programs that make decisions based on conditions. For example, a program can display messages like "It's a hot day" or "Drink plenty of water" if the temperature exceeds 30 degrees, and other messages for different ranges. Using parentheses to define boolean expressions and curly braces to group multiple actions ensures proper execution when conditions are met.

Optimizing Code Readability in Conditional Structures Conditional structures include 'if', 'else if', and 'else' clauses arranged hierarchically. While some prefer always using curly braces for clarity, others omit them when there's only one statement per clause to reduce visual clutter. Simplifying unnecessary code segments enhances readability; formatting adjustments such as aligning clauses symmetrically further improve aesthetics without altering functionality.

To simplify if statements, start by declaring variables clearly and use underscores in numbers for readability. Avoid scoping issues by defining boolean variables outside conditional blocks. Instead of using verbose if-else structures, initialize the variable with a default value and update it based on conditions to streamline code. For further improvement, replace entire if statements with concise boolean expressions directly assigned to the variable. Wrapping these expressions in parentheses enhances clarity without altering functionality.

The ternary operator in Java simplifies conditional assignments by replacing verbose if-else statements. For example, when categorizing customers based on income into 'first' or 'economy' class, instead of using multiple lines to check conditions and assign values, a single line can achieve this. The syntax involves writing the condition followed by a question mark (?), then specifying the value for true cases before adding a colon (:) and defining the false case value. This concise approach eliminates unnecessary code while maintaining clarity.

Understanding Switch Statements in Java Switch statements allow executing different code blocks based on the value of an expression, similar to if-else conditions. By declaring a variable and using cases for specific values (e.g., 'admin', 'moderator'), corresponding actions can be defined with break statements ensuring proper flow control. A default clause handles unmatched cases without requiring a break statement at its end.

Flexibility and Use Cases of Switch Statements Switch statements support various data types like strings or integers, enabling versatile applications such as role-based message displays or numeric operations. Without breaks between case clauses, execution continues through subsequent lines until encountering one—a behavior known as fall-through. This feature makes switch constructs both powerful and concise alternatives to nested if-else structures.

Understanding and Implementing FizzBuzz Logic The exercise involves creating a program that takes an input number and checks its divisibility by 3, 5, or both. If divisible by only 5, it prints "Fizz"; if only by 3, it prints "Buzz"; if divisible by both (e.g., 15), it outputs "FizzBuzz." Otherwise, the program simply returns the entered number. The initial implementation had a bug where specific conditions were not prioritized correctly in sequence—causing incorrect results for numbers like fifteen.

Optimizing Code with Trade-offs in Mind To fix prioritization issues in logic flow for FizzBuzz output correctness: place combined condition (divisible by both) first before individual ones to ensure accurate execution order. An alternative approach avoids repetition but introduces nested structures considered less readable—a trade-off between clarity versus avoiding redundancy arises here. Ultimately programming often requires balancing such strengths/weaknesses rather than achieving perfection.

For loops simplify repetitive tasks by executing a block of code multiple times. The structure includes initializing a counter variable, setting a condition for execution, and incrementing or decrementing the counter. By using concise variables like 'i', developers can control iterations efficiently to print outputs such as "Hello World" five times or display numbers sequentially or in reverse order. Adjustments to initialization values and conditions allow flexibility in loop behavior.

Understanding While Loops in Java While loops function similarly to for loops but differ in syntax. They are ideal when the number of iterations is unknown, unlike for loops which suit predefined iteration counts. For example, a while loop can continuously prompt user input until "quit" is entered.

Implementing and Optimizing While Loops To implement a while loop that checks user input against 'quit,' use string methods like equals() instead of comparison operators due to memory address differences between strings. Optimize by creating scanner objects outside the loop and converting inputs to lowercase with .toLowerCase(). This ensures efficient memory usage and case-insensitive comparisons.

Do-while loops in Java ensure that the code block executes at least once, regardless of whether the condition is true or false initially. Unlike while loops, which check conditions before execution and may not run if the condition is false from the start, do-while loops evaluate their conditions after executing their body. This makes them useful for specific scenarios where an initial action must occur before any checks are made. However, they are less commonly used compared to while loops.

To address the issue of unwanted input echoing, one solution is to use an if statement that checks whether the input equals "quit" before printing. Alternatively, reversing this logic allows for immediate termination using a break statement when "quit" is entered. The continue statement can be used to skip specific inputs like "pass," moving control back to the loop's start without terminating it or printing undesired outputs. Simplifying loops by setting their condition as always true (while(true)) ensures continuous execution until explicitly terminated by a break; however, caution must be taken to avoid infinite loops.

The for-each loop in Java simplifies iterating over arrays or collections by eliminating the need to declare a numeric counter, write boolean expressions, or manually increment counters. It requires defining a variable matching the type of array elements and automatically assigns each element to this variable during iteration. While it produces identical results as traditional loops like 'for' or 'while', its limitations include being forward-only (unable to iterate backward) and lacking access to item indices. In contrast, standard for-loops allow reverse traversal and provide both index values alongside items.

The mortgage calculator now includes basic error handling to ensure user inputs fall within specified ranges. For the loan amount, users must enter a value between $1,000 and $1 million; otherwise, they are prompted with an error message until valid input is provided. Similarly, for the annual interest rate, only values greater than 0 and up to 30 are accepted—invalid entries trigger repeated prompts for correction. Once all inputs meet these criteria (e.g., entering $1 million as a loan or 3.9% interest), the system calculates and displays monthly payments accurately.

Implementing Data Validation in Mortgage Calculator To ensure valid user input, an infinite loop is used to repeatedly prompt until a correct value is entered. For the principal amount, it must be between 1,000 and 1 million; for annual interest rate, between 1% and 30%; and for loan years, from one to thirty. Variables are declared outside loops to avoid scope-related compilation errors.

Improving Code Maintainability Through Modularization The main method becomes cluttered with lengthy validation logic affecting readability and maintainability. Breaking down code into smaller functions simplifies understanding by isolating specific tasks like data validation or calculations into distinct modules.

This section covers controlling program execution through comparison and logical operators, enabling the implementation of real-world rules. It introduces conditional statements like 'if' and 'switch' for decision-making processes within programs. Various loop types—'for', 'while', 'do-while,' and 'for-each loops—are explained to facilitate repetitive code execution efficiently. Additionally, it explores using break and continue statements to manage loop flow effectively.

Writing clean code is essential for creating programs that are not only functional but also maintainable and understandable by humans. The focus on clean coding involves restructuring messy, hard-to-maintain code into a more organized and elegant form. Using the example of extending a mortgage calculator with new features, techniques will be demonstrated to improve its structure while keeping it clear and efficient.