java learning

public class Demo
{
    public static void main(String[] args)
    {
        for(int i = 1988; i< 2019; i++) {
            if ((i%4==0 && i%100 != 0) || i%400 ==0) {
                System.out.println(i);
            }
        }
    }
}

public class Demo1
{
    public static void main(String[] args)
    {
        for(int i = 1; i <= 5; i++) {
             for(int j = 1; j <= i; j++) {
                System.out.print("@");
            }
            System.out.println();
        }
    }
}

public class Demo2
{
    public static void main(String[] args)
    {
        int[] arr = {79, 89}; // 数组用花括号， 数组定义 int[]
        double sum = 0;
        for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
        }
        
        double avg = sum/arr.length;
        
        System.out.println(avg);
    }
}

public class Demo2
{
    public static void main(String[] args)
    {
        int[] arr = new int[6]; // 定义
        Scanner sc = new Scanner(System.in); // 定义 Scanner
        
        for (int x = 0; x < arr.length; x++) {
          arr[x] = sc.nextInt(); // 获取下一个
        }
        
        int max = getMax(arr);
        int min = getMin(arr);
        int sum = getSum(arr);
        
        int avg = (sum - min - max)/(arr.length -2);
        
        System.out.println(avg);
    }
    
    public static int getSum(int[] arr)
    {
        int sum = 0;
        for (int i=0; i<arr.length; i++) {
          sum += arr[i];
        }
        
        return sum;
    }
    
    public static int getMin(int[] arr)
    {
        int min = arr[0];
        for (int = 1; i<arr.length; i++)
        {
            if (min < arr[i]) {
              min = arr[i];
            }
        }
        
        return min;
    }
}

public class Demo2
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in); // 定义 Scanner
        
        int week = sc.nextInt();
        
        if (week < 1 || week > 7) {
            System.out.println();
        } else if () {
        }
        
        switch (week) {
            case 1:
                break;
            case 2;
                break;
            default:
                System.out.println("xx");
        }
    }
}