如何根据输出的长度调整打印的 table 的长度（在控制台中打印）

Question

当我输入一个数字时，将打印一个 table，它应该如下图所示。 Expected output

我不知道如何根据输出的长度调整要打印的“-”的数量。我还尝试使用不同的数学计算，使用整数变量来增加字符数量并打印相同数量的“-”。

这是我的输出： Output

这是我的代码：

    Scanner keyboard = new Scanner(System.in);
    int num;
    char line = 45;
    StringBuilder sb = new StringBuilder();

    do {
        System.out.println("Enter a number between 1 and 30");
        num = keyboard.nextInt();
        if (num == 0) System.exit(0);
    } while (num < 1 || num > 30);


    //TOP LINES --> THIS IS THE PROBLEM
    for (int i = 0; i < num; i++) {
        for (int j = 0; j < num/4; j++) {
            sb.append(line);
        }
    }
    System.out.println(sb);

    //PRINTS FIRST PIPE
    System.out.printf("|");


    for (int n = 1; n <= num*num; n++) {
        System.out.printf(" %-3d|", n);
        if (n % num == 0 && n != num*num){
            System.out.println();
            System.out.printf("|");
        }
    }

    //BOTTOM LINES
    System.out.println("\n" + sb);

Answer 1

更改循环以计算“-”的数量

//TOP LINES --> THIS IS THE PROBLEM
for (int i = 0; i < num; i++) {
    for (int j = 0; j < num/4; j++) {
        sb.append(line);
    }
}
System.out.println(sb);


     >>>>>>>   TO <<<<<<<<

        //Determine the column size
    String largestValue = "" + (num * num);  // for 20, this is "400"
    int strLen = largestValue.length(); // for 20, this is 3 + 1 space+  for right '|'
    int width = (num * (strLen + 2));
    width++; // for right '|'
    //TOP LINES 
    for (int i = 0; i < width; i++) {
        System.out.print('_'); // I'm outputting an underscore
    }
    System.out.println("");
    System.out.print("|");
    for (int n = 1; n <= num; n++) {
        System.out.printf(" %-" + strLen + "d|", n);
    }
    System.out.println("");
    for (int row = 1; row <= num; row++) {
        System.out.print("|");
        for (int column = 1; column <= num; column++) {
            System.out.printf(" %-" + strLen + "d|", (row * column));
        }
        System.out.println("");
    }
    //bottom LINES 
    for (int i = 0; i < width; i++) {
        System.out.print('_');
    }
    System.out.println("");

如何根据输出的长度调整打印的 table 的长度（在控制台中打印）

How to adapt the length of a printed table based on the length of the output (print in console)

java

system.out