オンラインJavaコンパイラ

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

public class Main {
    public static void main(String[] args) {
        String name = "Alice";
        int age = 30;
        System.out.println(name + " is " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        int x = 10;
        if (x > 0) System.out.println("Positive");
        else if (x == 0) System.out.println("Zero");
        else System.out.println("Negative");
    }
}

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++)
            System.out.println("Count: " + i);

        String[] fruits = {"apple", "banana", "cherry"};
        for (String fruit : fruits)
            System.out.println(fruit);
    }
}

public class Main {
    static String greet(String name) {
        return "Hello, " + name + "!";
    }
    static String greet(String name, String greeting) {
        return greeting + ", " + name + "!";
    }
    public static void main(String[] args) {
        System.out.println(greet("Alice"));
        System.out.println(greet("Bob", "Hi"));
    }
}

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>(Arrays.asList("apple", "banana"));
        fruits.add("cherry");
        System.out.println(fruits.get(1));

        Map<String, Integer> person = new HashMap<>();
        person.put("age", 30);
        System.out.println("Age: " + person.get("age"));
    }
}

public class Main {
    static class Dog {
        String name, breed;
        Dog(String name, String breed) {
            this.name = name; this.breed = breed;
        }
        String bark() { return name + " says Woof!"; }
    }
    public static void main(String[] args) {
        Dog dog = new Dog("Rex", "Labrador");
        System.out.println(dog.bark());
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            int result = Integer.parseInt("not a number");
        } catch (NumberFormatException e) {
            System.out.println("Error: " + e.getMessage());
        } finally {
            System.out.println("Done");
        }
    }
}

import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        try (PrintWriter pw = new PrintWriter("output.txt")) {
            pw.println("Hello, File!");
        }
        try (BufferedReader br = new BufferedReader(new FileReader("output.txt"))) {
            System.out.println(br.readLine());
        }
    }
}

import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        int sum = nums.stream()
            .filter(n -> n % 2 == 0)
            .mapToInt(Integer::intValue)
            .sum();
        System.out.println("Sum of evens: " + sum);
    }
}