import java.nio.file.*;
import java.io.IOException;
import java.util.List;

public class ReadFileExample {
    public static void main(String[] args) {
        try {
            Path filePath = Paths.get("data.txt");
            List<String> lines = Files.readAllLines(filePath);

            for (String line : lines) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.nio.file.*;
import java.io.IOException;
import java.util.Arrays;

public class WriteFileExample {
    public static void main(String[] args) {
        try {
            Path filePath = Paths.get("output.txt");
            Files.write(filePath, Arrays.asList("Hello World", "This is a text file"), StandardOpenOption.CREATE);
            System.out.println("File written successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Files.write(filePath, Arrays.asList("New line added"), StandardOpenOption.CREATE, StandardOpenOption.APPEND);

#کاربرـپیشرفته

🆔 @javapro_ir
🆔 @group_javapro

String s = "hello";
s += " world";

String result = "";
for (int i = 0; i < 10000; i++) {
    result += i;
}

StringBuilder result = new StringBuilder();
for (int i = 0; i < 10000; i++) {
    result.append(i);
}

#کاربر_مبتدی

🆔 @javapro_ir
🆔 @group_javapro

String a = "hello";
String b = "hello";
String c = new String("hello");

System.out.println(a == b);     // true (به علت String Pool)
System.out.println(a == c);     // false (شیء جدید در Heap)
System.out.println(a.equals(c)); // true (برابری محتوا)

class User {
    String name;
    User(String name) {
        this.name = name;
    }
}

public class Test {
    public static void main(String[] args) {
        User u1 = new User("Ali");
        User u2 = new User("Ali");

        System.out.println(u1 == u2);        // false
        System.out.println(u1.equals(u2));   // false (تا زمانی که equals بازنویسی نشده باشد)
    }
}

@Override
public boolean equals(Object obj) {
    if (this == obj) return true;
    if (obj == null || getClass() != obj.getClass()) return false;
    User user = (User) obj;
    return name.equals(user.name);
}

#کاربر_مبتدی

🆔 @javapro_ir
🆔 @group_javapro

public class Counter {
    int count = 0;
}

public class Counter {
    static int count = 0;
}

public class Example {
    int instanceVar = 0;
    static int staticVar = 0;

    public void increment() {
        instanceVar++;
        staticVar++;
    }
}

public class Main {
    public static void main(String[] args) {
        Example a = new Example();
        Example b = new Example();

        a.increment();
        b.increment();

        System.out.println("a.instanceVar = " + a.instanceVar); // 1
        System.out.println("b.instanceVar = " + b.instanceVar); // 1

        System.out.println("a.staticVar = " + a.staticVar);     // 2
        System.out.println("b.staticVar = " + b.staticVar);     // 2
    }
}

Counter.count++;
System.out.println(Counter.count);

#کاربر_مبتدی

🆔 @javapro_ir
🆔 @group_javapro

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }

    public double add(double a, double b) {
        return a + b;
    }
}

class Animal {
    public void speak() {
        System.out.println("Animal speaks");
    }
}

class Dog extends Animal {
    @Override
    public void speak() {
        System.out.println("Dog barks");
    }
}

public class Test {
    public static void main(String[] args) {
        Animal animal = new Dog();
        animal.speak();  // خروجی: Dog barks
    }
}

#کاربرـپیشرفته

🆔 @javapro_ir
🆔 @group_javapro

final int MAX_USERS = 100;
MAX_USERS = 150; // خطا: نمی‌توان به متغیر final مقدار جدید داد

class Person {
    public final void printID() {
        System.out.println("ID printed.");
    }
}

class Student extends Person {
    // خطا: نمی‌توان متد final را override کرد
    public void printID() {
        System.out.println("Student ID");
    }
}

final class Utility {
    public static void log(String message) {
        System.out.println("LOG: " + message);
    }
}

// خطا: نمی‌توان از کلاس final ارث‌بری کرد
class CustomUtility extends Utility { }

#کاربرـپیشرفته

🆔 @javapro_ir
🆔 @group_javapro

public class Config {
    public static final String API_URL = "https://api.myapp.com/";
    public static final int MAX_LOGIN_ATTEMPTS = 5;
}

System.out.println("URL: " + Config.API_URL);
if (loginAttempts > Config.MAX_LOGIN_ATTEMPTS) {
    System.out.println("Too many failed attempts.");
}

public class Config {
    public final String API_URL = "https://api.myapp.com/";
}

Config cfg = new Config();
System.out.println(cfg.API_URL); // غیربهینه و غیرضروری

System.out.println(Config.API_URL); // ساده و مستقیم

public static final String DATABASE_NAME = "main.db";

#کاربرـپیشرفته

🆔 @javapro_ir
🆔 @group_javapro

final int x = 10;
x = 20; //  خطا

public class Example {
    public static void main(String[] args) {
        int number = 5; // not declared as final
        Runnable r = () -> System.out.println(number); //  مجاز چون effectively final است
        r.run();
    }
}

int number = 5;
number++; //  اکنون دیگر effectively final نیست
Runnable r = () -> System.out.println(number); //  خطای کامپایل

int[] counter = {0};
Runnable r = () -> counter[0]++;

#کاربرـحرفهـای

🆔 @javapro_ir
🆔 @group_javapro