Language

Introduction to Java

Introduction

Java is a general-purpose, class-based, object-oriented programming language designed for having lesser implementation dependencies. It is a compiled language and not an interpreted language. Java applications are compiled to bytecode that can be run on any platform that has a Java Virtual Machine (JVM).

Variables

Variables are used to store data in Java. They are declared using the var_name = value syntax. The data type of a variable must be declared, which makes it easy to write correct code.

For example, the following code declares a variable named name and assigns it the value “Hello, world!”:

String name = "Hello, world!";

Data Types

Java has a variety of data types, including:

  • Strings: A sequence of characters.
  • Numbers: Integers, floats, and double.
  • Booleans: True or False values.
  • Arrays: A collection of objects.
  • Collections: A collection of objects that can be manipulated using methods.

Operators

Java has a variety of operators, including:

  • Arithmetic operators: +, -, *, /, %
  • Comparison operators: ==, <, >, <=, >=, !=
  • Logical operators: and, or, not
  • Bitwise operators: &, |, ^, ~, <<, >>
  • Assignment operators: =, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=`

Control Flow

Java has a variety of control flow statements, including:

  • if statements: Used to execute code if a condition is met.
  • else if statements: Used to execute code if a condition is not met, but another condition is met.
  • else statements: Used to execute code if no conditions are met.
  • for loops: Used to iterate over a sequence of objects.
  • while loops: Used to iterate over a block of code while a condition is met.
  • do-while loops: Used to iterate over a block of code while a condition is met, at least once.
  • break statements: Used to exit a loop.
  • continue statements: Used to skip the current iteration of a loop.
  • return statements: Used to return from a function.

Functions

Functions are blocks of code that can be reused. They are defined using the def keyword. The def statement takes two arguments: the name of the function and a block of code.

For example, the following code defines a function named greet() that prints the string “Hello, world!”:

def greet():
    print("Hello, world!")

Classes

Classes are used to create custom data types. They are defined using the class keyword. The class statement takes two arguments: the name of the class and a block of code.

For example, the following code defines a class named Person that has two attributes: name and age:

class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    void printInfo() {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }
}

Object-Oriented Programming

Java is an object-oriented programming language. This means that it uses objects to represent data and behavior.

Android App Development

Java is a popular language for developing Android apps. The Android SDK provides a variety of tools and libraries that make it easy to develop Android apps using Java.

Web CGI Development

Java is also a popular language for developing web CGI applications. The Java Servlet API provides a variety of tools and libraries that make it easy to develop web CGI applications using Java.

Java is a popular language for a variety of other scenes, including:

  • Enterprise Application Development
  • Scientific Computing
  • Game Development
  • Networking
  • Security