Comprehensive understanding of Java technology: A guide from beginner to proficient

Java Technology Guide: A Comprehensive Overview from Basics to Advanced

Introduction:
Java is a widely used programming language that is cross-platform and object-oriented. and a strong ecosystem among many other advantages. This article will gradually introduce the core concepts and main technologies of Java from basic to advanced, and provide specific code examples to help readers get started quickly and understand Java programming in depth.

Part 1: Basic knowledge of Java

1. Variables and data types:
   Java variables need to be declared before use, and have a variety of data types, including integers, floating point numbers, Character, boolean, and reference types. Sample code:

int age = 25;
double price = 12.5;
char grade = 'A';
boolean isValid = true;
String name = "John";

2. Control flow:
   Java provides a variety of control flow statements, such as conditional statements (if-else, switch), loop statements (for, while, do -while) and jump statements (break, continue). Sample code:

if (score >= 90) {
    System.out.println("优秀");
} else if (score >= 80) {
    System.out.println("良好");
} else {
    System.out.println("及格");
}

for (int i = 0; i < 10; i++) {
    System.out.println(i);
}

while (count > 0) {
    System.out.println(count);
    count--;
}

3. Array:
   Java's array is a container that stores multiple data of the same type, and elements can be accessed by index. Sample Code:

int[] numbers = new int[5];
numbers[0] = 1;
numbers[1] = 2;
numbers[2] = 3;
numbers[3] = 4;
numbers[4] = 5;

String[] names = {"Alice", "Bob", "Charlie"};

Part 2: Object-Oriented Programming

1. Classes and Objects:
   Java is an object-oriented language that creates classes by defining classes and objects for programming. Sample code:

public class Person {
    private String name;
    private int age;

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

    public void sayHello() {
        System.out.println("Hello, my name is " + name);
    }
}

Person person = new Person("John", 25);
person.sayHello();

2. Inheritance and polymorphism:
   Java supports the inheritance relationship between classes. Subclasses can inherit the properties and methods of the parent class, and can use polymorphism to Implement dynamic binding. Sample code:

public class Animal {
    public void makeSound() {
        System.out.println("Animal makes sound");
    }
}

public class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Cat says Meow");
    }
}

Animal animal = new Cat();
animal.makeSound();

3. Interfaces and abstract classes:
   Java interfaces and abstract classes are important means to achieve polymorphism. The interface defines a set of method specifications, and the abstract class It can contain concrete methods and abstract methods. Sample code:

public interface Drawable {
    void draw();
}

public abstract class Shape implements Drawable {
    protected int x;
    protected int y;

    public Shape(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public void draw() {
        System.out.println("Drawing shape at (" + x + ", " + y + ")");
    }

    public abstract double area();
}

public class Circle extends Shape {
    private double radius;

    public Circle(int x, int y, double radius) {
        super(x, y);
        this.radius = radius;
    }

    @Override
    public double area() {
        return Math.PI * radius * radius;
    }
}

Shape shape = new Circle(0, 0, 5);
shape.draw();
System.out.println("Area: " + shape.area());

Part 3: Java advanced features

1. Exception handling:
   Java's exception handling mechanism can capture and handle exceptions in the program, ensuring The stability of the program during runtime. Sample code:

try {
    int result = divide(10, 0);
    System.out.println(result);
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
}

public int divide(int num1, int num2) {
    if (num2 == 0) {
        throw new ArithmeticException("Divisor cannot be zero");
    }
    return num1 / num2;
}

2. Input and output streams:
   Java provides a rich set of input and output stream classes, which can realize data reading and writing interaction with files, networks, etc. Sample code:

try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }
} catch (IOException e) {
    System.out.println("Error: " + e.getMessage());
}

try (BufferedWriter writer = new BufferedWriter(new FileWriter("file.txt"))) {
    writer.write("Hello, World!");
} catch (IOException e) {
    System.out.println("Error: " + e.getMessage());
}

3. Multi-threaded programming:
   Java's multi-threading mechanism can realize concurrent execution of programs and improve program performance and responsiveness. Sample code:

public class MyThread extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println(Thread.currentThread().getName() + ": " + i);
        }
    }
}

MyThread thread1 = new MyThread();
MyThread thread2 = new MyThread();
thread1.start();
thread2.start();

Conclusion:
This article provides a comprehensive overview of Java technology from Java basics, object-oriented programming to Java advanced features, and provides specific code examples. I hope this article can help readers get started quickly and understand Java programming in depth, and lay a good foundation for further learning Java.

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