Stack Overflow Asked by BENJAMIN WEED on January 5, 2022

I know this error has been asked a lot. I have looked at them but still don’t really understand how it applies to my problem. I am trying to write a program that creates a diamond pattern from a string.

public static String nameDiamond(String s) {
    int len = s.length();
    int i = 0;
    String out = "";
    while(i < len) { 
        out = out + s.substring(0, i + 1) + "n";
    while(i > 0) { 
        int numSpaces = len - i + 1;
        for(int j = 0; j < numSpaces; j++)
            out = out + " ";
        out = out + s.substring(len - i + 1, i - 1) + "n";
    return out;

Now my understanding of substring is, that it is structured like s.substring(startIndex, endIndex) and a cause of this error can be when the end index is less then the start but I don’t think this is the problem here. I also saw some causes of the error is when something does not exist but again I don’t think this is the problem. What am I missing?

When it is tested with "Marty" it says -1 and with "Bill Nye" it says -2. Would the space be causing this?

I looked at lots of other versions of the questions but the ones that seemed relevent were:

StringIndexOutOfBoundsException: string index out of range

StringIndexOutOfBoundsException: String index out of range: -1

But I don’t think they apply.

For reference, this is the problem:

One Answer

Here is one you can use as an example. It doesn't do exactly what you want but it will illustrate one important thing. For fixed width fonts, each row must be an odd number of characters. Otherwise they won't line up properly.

If n is an even number, this particular version will print the same diamond for n and n+1. It is also limited by the string of spaces.

public static void printDiamond(int len) {
    String str = "*";
    String space = "                              ";
    for (int i = 0; i < len/2 + 1; i++) {
        str = str+"**";
    str = str.substring(2);
    for(int i = 0; i < len/2; i++) {
        str = str.substring(2);

As you debug your program, use ubiquitous print statements to print the different variables such as indices and string lengths.

Answered by WJS on January 5, 2022

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