用eclipse打印一个空心正方形

Question

Answer 1

    String str ="";
    System.out.println("请输入边长：");
    Scanner input =new Scanner(System.in);
    int n=input.nextInt();
    for (int i = 1; i <= n; i++)
    {
        for(int j = 1; j <=n; j++)
        {
            if (i == 1 || i == n || j == 1 || j == n)
                 str += "*";
            else
                str+= " ";
        }
        str += "\n";
    }
    System.out.println(str);

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运行结果如下