请出几道java的基础题目

好的，以下是几道 Java 基础题目：

1. 编写一个 Java 程序，在控制台输出 “Hello, world!”。

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

2. 编写一个 Java 程序，计算1到100的累加和。

public class Sum {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 1; i <= 100; i++) {
            sum += i;
        }
        System.out.println("1到100的累加和为：" + sum);
    }
}

3. 编写一个 Java 程序，接收用户输入的两个数字，并计算它们的和、差、积、商。

import java.util.Scanner;
 
public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入第一个数字：");
        double num1 = scanner.nextDouble();
        System.out.print("请输入第二个数字：");
        double num2 = scanner.nextDouble();
 
        double sum = num1 + num2;
        double diff = num1 - num2;
        double product = num1 * num2;
        double quotient = num1 / num2;
 
        System.out.println(num1 + " + " + num2 + " = " + sum);
        System.out.println(num1 + " - " + num2 + " = " + diff);
        System.out.println(num1 + " * " + num2 + " = " + product);
        System.out.println(num1 + " / " + num2 + " = " + quotient);
    }
}