Java is a general-purpose, object-oriented programming language used to develop applications for the web, desktop, and mobile devices. It is one of the most popular programming languages in the world, used by millions of developers around the world. This article will discuss the core concepts of Java, in an effort to explain the language in detail.

What is Java?

Java is a class-based, object-oriented programming language. It is type safe and platform independent, meaning that code written in Java can be executed on any platform without the need for any modifications. This is due to the presence of the Java Virtual Machine (JVM), which acts as an interpreter between the code and the platform it is running on.

Java has a set of keywords and language constructs which are used to create the logic of a program. It also has several built-in data types, such as strings, integers, floats, and booleans. Java also supports a range of objects, including classes, interfaces, and patterns.

Variables and Data Types

In order to create a program, it is first necessary to declare variables. These are variables which can store data, such as numerical values, strings, or boolean values. Java has a range of data types which can be used to declare variables, including integer, float, string, boolean, and char.

Additionally, it is possible to create user-defined data types. These are custom data types which can be used to store a range of data, as defined by the programmer. Java also supports built-in variables which can be used to store objects such as classes, interfaces, and structs.

Control Flow Statements

Control flow statements are used to control the flow of execution within a program. Java has a range of control flow statements, including if/else statements, switch statements, for loops, do/while loops, try/catch blocks, and break statements.

These statements can be used to branch the program’s logic or repeat instructions as needed. They can also be used to jump to different instructions based on various conditions or execute instructions multiple times until a certain condition is met.

Object-Oriented Programming

Object-oriented programming (OOP) is a programming paradigm in which the focus of programming is on objects and data rather than procedures and algorithms. Java supports OOP concepts such as classes, objects, abstraction, encapsulation, inheritance, and polymorphism.

Objects are self-contained units of code which have state (data) and behavior (methods). Classes are templates which are used to define objects. Abstraction is the process of simplifying complex objects into more general ones. Encapsulation is the wrapping up of data and methods into a single unit. Inheritance allows objects to inherit characteristics from other classes. Polymorphism allows an object to take on many forms depending on the context.

Exception Handling

Exception handling is used in Java to handle errors or exceptional events which arise during the execution of a program. Java has a built-in exception class which allows programs to catch any errors or exceptional events and respond accordingly. The catch block contains code which will be executed when an error occurs.

Exception handling is an important part of programming as it allows programs to anticipate errors and respond accordingly without crashing or losing data.

Wrapper Classes

Wrapper classes are a special type of class which are used to wrap primitive data types. Primitive data types are the built-in data types in Java such as int and boolean. Wrapper classes provide methods to help convert primitive values into objects or to convert objects into primitive values.

Wrapper classes also provide methods to allow for invoke functional operations on primitive values such as converting from one primitive type to another or generating random numbers.

Generics

Generics is a technology which allows for the creation of generic data types and methods. Generics allow for type safety by ensuring that objects are correctly typed when they are created and referenced during program execution. This helps prevent errors caused by invalid type conversions as code is being executed.

Garbage Collection

Garbage collection is an automated process in Java which helps reclaim memory by freeing up memory which is no longer being used by an application. Garbage collection helps keep memory usage at manageable levels by freeing up memory which would otherwise remain unused. This helps improve performance by making more memory available for other parts of an application.

Java Concurrency Basics

Java concurrency is used to execute instructions in different threads simultaneously. Concurrency enables an application to process multiple instructions at the same time, as opposed to processing them one at a time. This improves performance by enabling instructions to be executed in parallel.

Java has built-in support for concurrency using the thread class, which allows for the creation of multiple threads and synchronization using locks, semaphores, and monitors.

Streams and Lambda Expressions

Streams and lambda expressions are a feature of Java 8 which allow for more efficient code by allowing operations on collections of data to be written in an efficient manner. Lambda expressions allow for lines of code to be written in a much more concise form than what would be possible with traditional Java code.

Streams are Java API classes which allow for the sequential and parallel processing of collections of data. Streams can help simplify complex operations on large collections of data.

Java I/O Basics

Input and output (I/O) operations in Java can be performed using streams and readers/writers. Streams are Java API classes which allow for efficient operations on files and other I/O resources such as URLs. Readers/writers allow for operations on text files or character streams such as strings.

Java also has several utility classes which contain methods for performing I/O operations (e.g., java.nio and java.io). These classes contain methods for reading from/writing to binary files and other I/O resources.

Reflection API

The reflection API is a set of tools in Java which allows code to inspect other parts of itself at runtime. The reflection API provides methods to allow code to discover class information such as field names, method signatures, and superclasses. Reflection also provides methods for performing dynamic method invocations at runtime.

Annotations

Annotations are a feature of Java which allow certain meta-data to be included in class definitions. Annotations can be used to provide more detailed information about the classes they refer to (e.g., @Override) or provide custom features (e.g., @Deprecated). Annotations are used extensively in Java libraries and frameworks.

Native Methods

Native methods are methods written in languages other than Java but which can be called from within Java code. Native methods help to improve performance by allowing code to access system resources which are not available in pure Java code (e.g., system calls or hardware operations). Native methods are often written in C or C++.

Security Manager

The Security Manager is part of the Java Runtime Environment (JRE) which provides support for security within Java applications. The security manager checks incoming code before it is allowed to execute, in an effort to prevent untrusted code from executing within a program.

Class Loaders

Class loaders are a special type of class which allow programs to load class files during runtime. Class loaders allow programs to dynamically load classes into memory when they are needed rather than loading them all at program start up.

Networking Basics in Java

Java provides two methods for creating applications which communicate over networks – sockets and servlets. Sockets provide access to low-level network functions such as creating client-server communications or opening raw network connections. Servlets provide support for web applications through HTTP requests and responses.

JDBC Basics

Java Database Connectivity (JDBC) is an API used for connecting Java applications to databases. JDBC provides an interface which allows applications to execute SQL queries on databases as well as providing support for transactions, stored procedures, and other JDBC features.