Building Better Boxes
Your friend is right, and there's ways to parameterize the code to make it more useful. Consider three things:


Don't print each character - build a block of text up, and print the block (note that adding a newline to the string \n works as well as a System.out.println())
You can input the text to repeat as a parameter to the function...
It is common practice to have loops from 0 to 1-less-than-the-limit like for (int i = 0; i &lt; limit; i++) {....} and not from 1 to the limit for (int i = 1; i &lt;= limit; i++) {...}. Your loop is not wrong.... but it is unconventional.


So, take your function:


public static void printLine(int length) 
{
    for (int i = 1; i &lt;= length; i++) 
    {
        System.out.print("*");
    }       
    System.out.println();
}



And apply the three concepts above... and we get:

public static String repeatText(String text, int count) {
    StringBuilder output = new StringBuilder();
    for (int i = 0; i &lt; count; i++) {
        output.append(text);
    }       
    return output.toString();
}


Now, that function can be used as the basis for a bunch of things....


your top-and-bottom lines of the box.
the inside-content of the other lines of the box
the repeating rows inside the box


Consider your printBox function:


public static void printBox(int length, int height) 
{
    printLine(length);

    for (int i = 1; i &lt;= height - 2; i++) 
    {
    System.out.print("*");     
        for (int j = 1; j &lt;= length - 2; j++) 
        {
            System.out.print(" ");
        }
        System.out.println("*");
    } 
    printLine(length);     
}



Let's use the same 3 principles I listed earlier, but let's also use the new repeatText function....

public static String buildBox(int length, int height)  {
    String topAndBottom = repeatText("*", length) + "\n";
    String middle = "*" + repeatText(" ", length - 2) + "*\n";
    String box = topAndBottom + repeatText(middle, height - 2) + topAndBottom;
    return box;
}


Now, you can print that box just once with:

System.out.print(buildBox(length, height));


There are still issues, like what happens if the length or height are less than 2? That would be a problem. Consider ways to avoid that, or handle that.