简单的一些 java 代码

1. 输出 Hello World：

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

2. 计算两个数的和：

import java.util.Scanner;

public class AddTwoNumbers {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter first number: ");
        int num1 = input.nextInt();
        System.out.print("Enter second number: ");
        int num2 = input.nextInt();
        int sum = num1 + num2;
        System.out.println("Sum of " + num1 + " and " + num2 + " is " + sum);
    }
}

3. 判断一个数是奇数还是偶数：

import java.util.Scanner;

public class CheckOddEven {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = input.nextInt();
        if (num % 2 == 0) {
            System.out.println(num + " is even");
        } else {
            System.out.println(num + " is odd");
        }
    }
}

4. 计算阶乘：

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = input.nextInt();
        int factorial = 1;
        for (int i = 1; i <= num; i++) {
            factorial *= i;
        }
        System.out.println(num + "! = " + factorial);
    }
}

5. 判断一个数是否是质数：

import java.util.Scanner;

public class CheckPrime {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = input.nextInt();
        boolean isPrime = true;
        if (num < 2) {
            isPrime = false;
        } else {
            for (int i = 2; i <= Math.sqrt(num); i++) {
                if (num % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }
        if (isPrime) {
            System.out.println(num + " is prime");
        } else {
            System.out.println(num + " is not prime");
        }
    }
}