Complete Core Java Tutorial for Beginners and Experienced

Core Java is a feature of the Java programming language that can be used to create general-purpose applications. The primary focus of core Java is to develop apps with Java Standard Edition and OOPs. Learn the concepts to build basic apps with this complete Core Java tutorial for beginners. Explore further with our Core Java Course Syllabus.

Getting Started to Core Java

Core Java is a superset of the Java language. Here is an overview of our Core Java Tutorial:

• Fundamentals of Core Java
• Object Oriented Programming in Core Java
• Core Java APIs
• Advanced Concepts in Core Java
• Applications of Core Java
• What is Beyond Core Java
• Importance of Learning Core Java

Recommended: Core Java Online Course Program.

Fundamentals of Core Java

Data types, OOP, operators, exception handling, swing, threading, and collections are some of the subjects covered in Core Java. Web services, database connectivity, JSP, Servlets, EJB, and other subjects are covered in Advanced Java. Applications. A user can create certain general-purpose apps with the help of Core Java. 

Syntax and Structure of Core Java

The core Any Java developer must understand the fundamentals of Java syntax and structure. 

Class Definition

• Classes are used to organize all Java programs. A class is an object creation blueprint.
• A class that is accessible from any location is declared via the public class keyword.
• The filename and the public class name (MyClass.java, for example) must match.

Example:

public class MyClass {

    // Class members (variables and methods) go here

}

main Method

• The main method of a Java application is its entrance point.
• It’s the starting point for execution.
• Its signature needs to be public static void main(String[] args).

Example:

public class MyClass {

    public static void main(String[] args) {

        // Code to be executed goes here

    }

}

Key Elements in Core Java Syntax

Below are the important elements in Core Java syntax:

Statements:

• A statement is a comprehensive directive that carries out a specific action.
• Semicolons (;) are used to conclude statements.

Example:

int x = 10;

System.out.println(“Hello, World!”);

Blocks:

• A collection of statements encased in curly braces ({}) is called a block.
• Blocks specify control flow and variable scopes.

Example:

if (x > 5) {

    System.out.println(“x is greater than 5”);

}

Variables:

• Data is stored in variables.
• They have a name and a data type.

Example:

int age = 30;

String name = “John Doe”;

boolean isTrue = true;

double pi = 3.14159;

Operators:

Variables and values are subject to operations by operators.

Examples:

• Arithmetic operators: +, -, *, /, %
• Relational operators: ==, !=, >, <, >=, <=
• Logical operators: && (and), || (or), ! (not)
• Assignment operators: = , +=, -=

Control Flow: 

The order in which statements are performed is decided by control flow statements.

Examples:

• if, else if, else: Conditional execution.
• for, while, do-while: Loops for repeated execution.
• switch: Multi-way branching.
• break, continue: Loop control.

Comments: 

• The compiler ignores comments, which are used to explain code.
• Comments in a single line: // This is a remark.
• Comments with multiple lines: /* This is a comment with several lines */

Methods: 

• A set of code that carries out a certain task is included in methods.
• They are able to return values after receiving parameters.

Example:

public static int add(int a, int b) {

    return a + b;

}

Keywords:

• Reserved terms having predetermined meanings are known as keywords.

Examples: Public, static, void, int, class, if, else, for, while, and return.

Packages and Imports:

• Classes are arranged into namespaces by packages and imports.
• You can utilize classes from other packages by using the import statement.

Example:

import java.util.Scanner;

Object Creation:

• Classes are instances of objects.
• To create objects, use the “new” keyword.

Example:

Scanner input = new Scanner(System.in);

Example Program with Core Java

public class HelloWorld {

    public static void main(String[] args) {

        System.out.println(“Hello, World!”);

        int num1 = 5;

        int num2 = 10;

        int sum = num1 + num2;

        System.out.println(“The sum is: ” + sum);

    }

}

Explanation:

• Class definition (public class HelloWorld)
• main method
• Variable declaration and assignment
• Arithmetic operation
• Output using System.out.println()

Writing efficient Java code requires an understanding of these basic components of core Java.

Suggested: Core Java Interview Questions and Answers.

Object Oriented Programming in Core Java

Object-Oriented Programming (OOP) is a programming paradigm built around the concept of “objects,” which can contain data and code: data in the form of fields (attributes) and code in the form of procedures (methods). 

Four Pillars in Core Java

Java is a strongly object-oriented language, and understanding OOP principles is essential for effective Java development. Here are the pillars of Core Java:

Encapsulation

Encapsulation is the process of combining data (attributes) and methods that work with that data into a single unit known as a class.

• By using public methods (getters and setters), it helps conceal an object’s internal implementation details and offers controlled access to its data.
• This improves code maintainability and shields data from unintentional alteration.

Inheritance

This makes it possible for a class (subclass or derived class) to inherit traits and attributes from a base class or superclass. 

• It creates a “is-a” link between classes and encourages code reuse.
• Java allows for the implementation of interfaces, which offer a type of multiple inheritance, but it also offers single inheritance, meaning that a class can inherit from just one superclass.

Polymorphism

Polymorphism means many forms. It describes an object’s capacity to assume several forms in OOP.

Java allows for two different kinds of polymorphism:

• Compile-time polymorphism (method overloading): Multiple methods in the same class may have the same name but distinct parameters due to it.
• Runtime polymorphism (method overriding): It is the ability of a subclass to implement a method that is already defined in its superclass.

Code that is more flexible and adaptive is made possible via polymorphism.

Abstraction

This entails displaying simply an object’s key features while concealing intricate implementation details. It is more concerned with “what” an object does than “how” it accomplishes it.

• Abstract classes and interfaces are two ways to accomplish abstraction in Java.
• Without having to know the background details, abstraction allows the user to concentrate on the important aspects of the object.

Advantages of OOPs in Core Java

The main benefits of OOPs are as follows:

• Code Reusability: By allowing you to reuse existing code, inheritance saves time and effort during development.
• Modularity: OOP encourages the development of code that is simpler to comprehend, update, and debug.
• Maintainability: By lessening the effect of modifications, encapsulation and abstraction improve code maintainability.
• Flexibility: Code that can handle a variety of scenarios is made more flexible and adaptive through polymorphism.
• Real-world Modeling: OOP enables you to naturally and intuitively represent real-world entities and their relationships.

Comprehending these ideas is essential for any Java developer.

Memory Management in Core Java

One of the most important features of the Java Virtual Machine (JVM) is memory management. Java automates memory allocation and deallocation, greatly lowering the possibility of memory leaks in contrast to languages like C or C++ where developers must do it manually. 

JVM Memory Structure

Memory is separated into multiple runtime data sections by the JVM. The following are the most pertinent to memory management:

Heap: 

• This is where arrays and objects are kept. 
• All threads share this area of memory, which is the largest.
• The main location where rubbish is collected is the heap. 

Stack:

• Every thread has a unique stack. 
• It keeps track of partial results, method call details, and local variables.
• It is automatically handled; a method’s stack frame is removed when it is finished. 

Method Area (Metaspace):

• It is referred to as Metaspace in Java 8 and beyond.
• Class-level data, including class structures, method bytecode, and static variables, are stored in the method area (metaspace).

Importance of Understanding Memory Management

Performance Optimization: 

Writing more effective code can be achieved by having a better understanding of memory management.

• The trash collector’s workload can be decreased by avoiding pointless object creation and limiting object lifetimes. 

Avoiding Memory Leaks: 

Java’s automatic garbage collection greatly lowers the possibility of memory leaks, but it is still possible to create circumstances in which objects are inadvertently kept.

• Preventing these problems requires an understanding of object references and lifecycles.

Debugging: 

Effective debugging of memory-related problems requires knowledge of the JVM’s memory architecture and garbage collection mechanism. 

Related Course: Java Training in Chennai

Core Java APIs

In essence, the standard libraries included with the Java Development Kit (JDK) are what we mean when we talk about Core Java APIs. Developers can create applications using a wide variety of pre-built classes and interfaces that these APIs offer.

What are Java APIs?

• The term “application programming interface” (API) refers to a group of pre-written Java code that may be used in your programs.
• They are made up of methods, interfaces, and classes that offer particular functions.
• They assist developers to avoid “reinventing the wheel” by providing ready-to-use solutions for typical tasks.   

Core Java APIs

The core Java APIs are those that are included in the Java Standard Edition (Java SE).

They offer necessary functions for jobs like:

• Input/output operations
• Networking
• Data manipulation
• Collections
• Multithreading   
• And much more.

Key Java API Packages

The following are a few of the most popular Java API packages:

java.lang: 

• Every Java program automatically imports this essential package.
• Important classes like String, Math, Object, and Thread are included.

java.util:

Numerous utility classes are available in this package, such as:

• Collections (sets, maps, and lists).
• Time and date utilities.
• Generation of random numbers.
• And more.

java.io: 

• This package offers classes for operations involving input and output, including:
• Examining and creating files
• Using streams

java.net: 

• This package offers networking operations classes such
• Using URLs
• Establishing sockets

java.nio: 

• This package offers non-blocking alternative I/O operations, which are utilized in high-performance applications.

java.sql: 

• This package offers classes for using JDBC (Java Database Connectivity) to work with databases.

Importance of Java APIs:

Some of the significance of Java APIs:

• Enhanced Productivity: APIs make it simple and quick for developers to incorporate new features into their apps.
• Code Reusability: APIs encourage code reuse, which cuts down on the time and effort required for development.
• Standardization: Java code is more portable and maintained thanks to Java APIs, which offer a standardized method for carrying out routine activities.

All things considered, the Java APIs are an essential part of the Java platform that let programmers create reliable and effective programs.

Recommended: API Training in Chennai.

Advanced Core Java Tutorial for Experienced

As you progress beyond Core Java’s foundations, you come across ideas that let you create programs that are more intricate, reliable, and effective. 

Important Advanced Core Java Ideas:

Some of the advanced concepts in Core Java are as follows:

Multithreading and Concurrency:

• This enables parallel processing by running several threads at once.
• Among the most complex subjects are:
  • Thread synchronization (with synchronized locks).
  • Concurrency utilities (such as the package java.util.concurrent)
  • Atomic variables, executors, and thread pools.

Java Collections Framework (Advanced):

This entails knowing sophisticated collection classes and interfaces in addition to simple lists and maps.

• Putting in place custom collections.
• Use concurrent collections to ensure thread safety.
• Use of the Stream API with collections.

Input/Output (I/O) and NIO:

Advanced I/O functions:

• java.nio (New I/O) for I/O activities requiring high performance.
• Buffers and channels.
• Asynchronous I/O.

Reflection:

The capacity to analyze and change an object’s or class’s behavior in real time. Frameworks and libraries utilize this to execute code dynamically.

Java’s reflection functionality, which enables a running Java program to analyze and alter its own structure and behavior, is a formidable but potentially complicated feature. In essence, it lets you “look inside” objects and classes while they’re running.

• Introspection: During runtime, a Java program can examine its own elements, including classes, interfaces, fields, and methods, thanks to reflection.
• Dynamic Manipulation: Reflection allows you to do more than just inspect; it also allows you to construct objects, call methods, and access or change fields dynamically, even when their access modifiers (like private) would typically make this impossible.

Annotations: 

Java annotations give you the ability to include metadata in your code. The runtime environment, tools, and compiler can all use this metadata to give more details about your code.

Types of Annotations: 

• Built-in Annotations such as @Override, @Deprecated, @SuppressWarnings, @SafeVarargs, @FunctionalInterface.
• Meta-Annotations such as @Retention, @Target, @Documented, and @Inherited.
• Custom Annotations that we can create our own.

Generics: 

Type safety at compile time is ensured via generics, which let you write classes, interfaces, and methods that can handle different data types.

Core Concepts of Generics in Core Java

Generic Classes: Classes that can function on a parameterized type are known as generic classes.

Example: ArrayList<T>, where T is the type parameter.

Generic Methods: Methods that can function on a parameterized type are known as generic methods. The method’s return type comes after the type parameter.

Type Parameters: They serve as stand-ins for the real types. Usually, single uppercase letters like T, E, K, and V are used to symbolize them.

Bounded Types: You can limit the kinds that can be used with a generic class or function by using bounded types. By specifying an upper bound using the extends keyword, you can restrict the types to implementations of an interface or subclasses of a particular class.

Wildcards: Unknown kinds are represented by wildcards (?). When working with generic types, they offer freedom.

• ? extends T: Upper bounded wildcard.
• ? super T: Lower bounded wildcard.
• ?: Unbounded wildcard.

Type Erasure: Generic type information is deleted by the Java compiler during compilation. We refer to this procedure as type erasure. Type parameters are substituted by the compiler with their bounds or, in the absence of bounds, with Object.

Lambda Expressions and Functional Interfaces:

Java 8 introduced two important additions that greatly expand the language’s capabilities and allow for a more functional programming style: lambda expressions and functional interfaces. 

Functional Interfaces:  An interface with precisely one abstract method is called a functional interface. Although not required, the @FunctionalInterface annotation is advised. It assists the compiler in confirming that the interface satisfies the requirements for being a functional interface. 

Examples:

• Runnable: A task that can be carried out is represented by the term “runnable.”
• Consumer<T>: Indicates an operation that takes one input argument and doesn’t produce any output.
• Predicate<T>: Denotes a function of one argument with boolean values.
• Function<T, R>: A function that takes one input and returns a result is represented.

Lambda Expressions: Anonymous functions known as lambda expressions offer a succinct means of expressing instances of functional interfaces.

Syntax:

(parameters) -> expression

(parameters) -> { statements; }

Java Module System (Jigsaw Project):

With the release of Java 9, the Java Module System, also referred to as Project Jigsaw, introduced a major modification to Java. Large codebases, dependency management, and the size of the Java Runtime Environment (JRE) were among the issues it sought to resolve.

• module-info.java: The module descriptor, module-info.java, is a file that includes details about the module’s name, dependencies, and exported packages.
• requires: A reliance on another module is declared using this keyword in module-info.java.
• exports: Module-info.java contains a term that indicates which packages other modules can access.
• jlink: A program for making unique runtime graphics.

Exception Handling (Advanced):

Core’s advanced exception handling Java is not just about try-catch blocks. It includes best practices that result in applications that are more reliable, maintainable, and easy to use.

Custom Exception: For controlled exceptions, extend the Exception class; for unchecked exceptions, extend the RuntimeException class.

public class InsufficientFundsException extends Exception {

    public InsufficientFundsException(String message) {

        super(message);

    }

}

Exception Chaining: Make use of the exception class’s constructor, which takes a Throwable argument.

try {

    // … some code that might throw IOException …

} catch (IOException e) {

    throw new MyDatabaseException(“Failed to read data”, e);

}

Try-with-Resources:

• Initialize the resources inside the attempt() block.
• The AutoCloseable interface must be implemented by the resource.

try (BufferedReader reader = new BufferedReader(new FileReader(“file.txt”))) {

    // … read from the file …

} catch (IOException e) {

    // … handle exception …

}

Best Practices for Advanced Exception Handling in Core Java

• Catch Specific Exceptions: Unless it is absolutely required, do not capture general exceptions such as Exceptions.
• “Throw Early, Catch Late”: It refers to the practice of identifying mistake conditions early on and throwing exceptions.
• Use a logging framework (such as Log4j or SLF4j) for logging exceptions.
• Avoid Empty Catch Blocks: Log the exception or rethrow it.
• Use Finally Blocks for Cleanup: Make sure that important cleanup code, such closing resources, is always run by using finally blocks.

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Applications of Core Java

The core Java is widely used in many different applications because of its adaptability. Below is a summary of several important areas:

• Desktop GUI Applications: Java offers graphical user interface (GUI) development tools such as Swing and JavaFX.
• Scientific Applications: Java is frequently used in applications related to physics, chemistry, and bioinformatics.
• Gaming Applications: Java is used in the creation of games, especially those that are played online and on mobile devices.
• Embedded Systems: Blu-ray players and smart cards are examples of embedded systems.

What is Beyond Core Java

In general, when we discuss “Beyond Core Java,” we mean the parts of Java development that go beyond the basic libraries and grammar. This includes a variety of ideas and technologies that let programmers create increasingly intricate, enterprise-level applications.

Java Enterprise Edition, also known as Jakarta EE

It is a platform that offers runtime environments and APIs for creating and implementing extensive, distributed enterprise applications. 

• Servlets and JavaServer Pages (JSPs) for web development.   
• Enterprise JavaBeans (EJBs) for business logic.   
• Java Persistence API (JPA) for database interaction.

Java Frameworks

Frameworks that offer pre-built components and architectural patterns, such as Spring and Hibernate, streamline and expedite Java development.

• Web services, microservices, and business applications are all frequently built with Spring, in particular. 

Web Services

Through a network, these services allow various applications to communicate with one another.

• Web services are created with Java utilizing RESTful APIs and SOAP.

Microservices

In this architectural style, applications are constructed as a group of discrete, stand-alone services. 

• Java is a good choice for creating microservices because of frameworks like Spring Boot. 

Big Data

• Numerous big data platforms, such Apache Spark and Hadoop, employ Java to handle and analyze massive information.

Cloud Computing

Because Java supports platforms like Google Cloud Platform (GCP), Microsoft Azure, and Amazon Web Services (AWS), it is frequently utilized in the development of cloud-based applications.

Advanced Concurrency

This is working with multithreaded apps that are really advanced. This calls for a thorough comprehension of the java.util.concurrent package.

Explore our advanced Java interview questions and answers.

Importance of Learning Core Java

Learning Core Java is still very significant in the software development industry for a number of strong reasons:

• Foundational Knowledge: The essential building blocks for comprehending the concepts of object-oriented programming (OOP) are provided by Core Java. 
• Widespread Usage: Java is widely utilized in a number of sectors, including e-commerce, healthcare, and finance.
• Platform Independence: Java is very flexible due to its “write once, run anywhere” (WORA) feature. 
• Strong Ecosystem: Java has a sizable and vibrant community that offers a wealth of frameworks, libraries, and tools.
• Career Opportunities: Due to the growing demand for Java developers, there are many employment openings with good pay.
• Foundation of Advanced Java: Learning more complex Java technologies, such Java EE (Enterprise Edition) and Android development, requires a solid grasp of Core Java.
• Versatility: Java’s adaptability enables its usage in a number of fields such as web development, mobile app development, desktop applications, and big data processing.

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Conclusion

Acquiring knowledge The core Java provides a strong foundation for a successful career in software development and opens access to a wide range of options. Learn the fundamentals with this core Java tutorial and begin your career with our Core Java training in Chennai.