在空心矩形Java中打印居中的字符串

Question

I am working on a java program in which I am trying to utilize a header made of asterisks.

I would like to output a message in the center of the header but am not completely sure how to go about doing this.

static void header(String msg) {
    int h = 3;
    int w = 60;  

    for(int j = 1; j <= h; j++)
    {  
        for(int i = 1; i <= w; i++)
        {
            if(j == 1 || j == h || i == 1 || i == w)  
            {
                System.out.print("*");
            }
            else
            {
                System.out.print(" ");
            }
        }
        System.out.println();
    }   
}

So this header will print an asterisk, hollow rectangle 60 wide and 3 tall. I would like to format this as a custom method so I can reference this easily throughout the program. As you can see I have formatted the frame, so the issue is getting the string in there and centering it inside the frame. I sort of have an idea that I need to use msg.length() and possibly a printf() to do this but I'm not sure how to go about this.

Answer 1

Something like this should work:

private void printMessage(final String message) {

    String[] lines = message.split("\\r?\\n");

    int maxWidth = Arrays.stream(lines).mapToInt(String::length).max().getAsInt();

    System.out.println(repeatString("*", maxWidth + 2));

    for(final String line : lines) {
        int lengthDiff = maxWidth - line.length();
        System.out.print("*" + repeatString(" ", (lengthDiff / 2)) + line + repeatString(" ", (lengthDiff / 2)) + "*\n");
    }

    System.out.println(repeatString("*", maxWidth + 2));
}

private String repeatString(final String string, final int repetitions) {
    return new String(new char[repetitions]).replace("\0", string);
}

Testing:

String message = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.\n" +
                 "Suspendisse volutpat lobortis sem at gravida. Aenean aliquet erat justo,\n" +
                 "id ultricies mi ullamcorper eu. Mauris scelerisque accumsan metus vitae congue. Vestibulum\n";

printMessage(message);

Output:

********************************************************************************************
*                 Lorem ipsum dolor sit amet, consectetur adipiscing elit.                 *
*         Suspendisse volutpat lobortis sem at gravida. Aenean aliquet erat justo,         *
*id ultricies mi ullamcorper eu. Mauris scelerisque accumsan metus vitae congue. Vestibulum*
********************************************************************************************

Answer 2

Instead of printing the box first, you might want to print the top, the text and the bottom. To print the text (the center rows) you can use this

    if (msg.length() > (w-2)) {
        msg = msg.substring(1, w-2);
    }
    int space=(w-2-msg.length())/2;
    System.out.printf("%s%" + (space + msg.length()) + "s%" + (w - (space + msg.length())) + "s", "*", msg, "*");

Answer 3

Using what you've provided, you can construct your header by considering the amount of padding you will need in order to center your text. When you've reached this amount you will be at approximately the center of the header, then you can start printing characters from your message

---

This solution will only print on the middle row, based on your comment:

"No, the only thing I "know" is which line the text will be on (row 2)"

But hopefully the below changes can help you arrive at a final solution

public static void main(String[] args){
        header("Test Message");
        header("This message has more than sixty characters causing the header to grow");
    }

    static void header(String msg) {
        int headerHeight = 3;
        int headerWidth = msg.length() > 60 ? msg.length() + 60 : 60;
        int paddingRequired = (headerWidth - msg.length() - 2) / 2;
        paddingRequired++; //To account for the boundary asterisk

        for(int rowIndex = 1; rowIndex <= headerHeight; rowIndex++) {
            for(int columnIndex = 1; columnIndex <= headerWidth; columnIndex++) {
                //Is this one of the asterisks at the edges of the middle row
                boolean isBoundaryAsterisk = (columnIndex == 1 || columnIndex == headerWidth);
                if((rowIndex == headerHeight) || (rowIndex == 1) || isBoundaryAsterisk) {
                    System.out.print("*");
                }
                else if((columnIndex > paddingRequired) && ((columnIndex - paddingRequired - 1) < msg.length())) {
                    System.out.print(msg.charAt(columnIndex-paddingRequired - 1));
                }
                else {
                    System.out.print(" ");
                }
            }
            System.out.println();
        }
    }

---

Example output:

 ************************************************************ * Test Message * ************************************************************ ********************************************************************************************************************************** * This message has more than sixty characters causing the header to grow * ********************************************************************************************************************************** 

Note that the second example is greater than your initial 60, but the width of the header will grow to ensure spaces will be included