Java主流技术学习涵盖基础编程、面向对象、集合框架、异常处理与IO流、多线程编程及实战项目，全面掌握Java核心特性与应用实践。

Java基础编程：从零开始，了解Java的语法基础，包括数据类型、变量、运算符、流程控制、数组等基本概念。

Java 是一种强类型语言，使用变量前必须声明其类型。以下是Java的基本数据类型示例：

public class DataTypeExample {
    public static void main(String[] args) {
        int age = 25;
        double height = 165.5;
        char grade = 'A';
        boolean isStudent = true;

        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Grade: " + grade);
        System.out.println("Is Student: " + isStudent);
    }
}

运算符与流程控制

Java提供多种运算符，用于执行基本算术、比较和逻辑操作。流程控制语句包括if、else、switch和循环（for、while、do-while）。

数组

数组用于存储和操作一系列值，可通过下标访问元素：

public class ArrayExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        for (int i = 0; i < numbers.length; i++) {
            System.out.println("Number at index " + i + ": " + numbers[i]);
        }
    }
}

面向对象编程是Java的核心，涉及类、对象、封装、继承和多态。

类与对象

类是对象的模板，对象是类的实例：

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

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

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

public class Main {
    public static void main(String[] args) {
        Student student = new Student("John Doe", 20);
        student.introduce();
    }
}

封装

封装是将数据和操作数据的方法绑定在一起：

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

    // Getter and Setter
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

Java 集合框架提供了丰富的数据结构，如ArrayList、HashSet、HashMap等。

示例代码

import java.util.*;

public class CollectionExample {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        HashMap<String, Integer> fruitPrices = new HashMap<>();
        fruitPrices.put("Apple", 1.0);
        fruitPrices.put("Banana", 0.5);
        fruitPrices.put("Cherry", 2.5);

        System.out.println("Fruits: " + fruits);
        System.out.println("Prices: " + fruitPrices);
    }
}

Java使用try, catch和finally处理异常，输入输出流用于读写数据。

示例代码

public class ExceptionHandlingExample {
    public static void main(String[] args) {
        try {
            divide(10, 0);
        } catch (ArithmeticException e) {
            System.out.println("Cannot divide by zero.");
        }
    }

    public static void divide(int a, int b) throws ArithmeticException {
        int result = a / b;
        System.out.println("Result: " + result);
    }
}

import java.io.*;

public class IOStreamExample {
    public static void main(String[] args) {
        try {
            PrintWriter writer = new PrintWriter(new FileWriter("output.txt"));
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

            System.out.println("Enter your text:");
            String input = reader.readLine();
            writer.println(input);
            writer.flush();

            System.out.println("Your text has been saved to output.txt.");
        } catch (IOException e) {
            System.out.println("An error occurred while reading or writing.");
        }
    }
}

多线程编程可以提高程序执行效率，Java使用Thread类来创建和管理线程。

示例代码

public class ThreadExample {
    public static void main(String[] args) {
        Thread thread1 = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                System.out.println("Thread 1: " + i);
            }
        });

        Thread thread2 = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                System.out.println("Thread 2: " + i);
            }
        });

        thread1.start();
        thread2.start();
    }
}

构建Web应用、游戏或图形界面等，综合运用Java的主流技术。

示例代码（Web应用）

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HelloWorldServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.getWriter().println("<html><body><h1>Hello, World!</h1></body></html>");
    }
}

通过完成实际项目，开发者可以更好地理解Java的特性如何协同工作，从而提高编程技能和解决实际问题的能力。