Create long[] Array with Stringbuilder

Question

I want to create a long[] Array with the Stringbuilder, but with this code i get "java.lang.NumberFormatException:"

protected long[] getpattern(int numbercount, int value) {
        StringBuilder longstringbuilder = new StringBuilder();

        while(numbercount > 0) {
            longstringbuilder.append("100, ");
            longstringbuilder.append(value + ", ");
            numbercount--;
        }
            longstringbuilder.append("100");

        String longstring = longstringbuilder.toString();

            long[] pattern = new long[] {Long.parseLong(longstring)};




        return pattern;

    }

How can i fix that? Thanks for your answers

Why do you think that your syntax is going to work? You are making an array with a single item in it, and the item comes from parsing a long and incorrect string, which causes the exception. Use a list instead of string builder. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Dec 17, 2017 at 17:23
Why would you use a type designed for manipulating text to build an array of numbers? What are you trying to accomplish here? Why not use long[] array = new long[numbercount]; and then populate it in a loop? (Or numbercount * 2 if you want a value of 100 between each value value.) — Jon Skeet
– Jon Skeet, Commented Dec 17, 2017 at 17:26

Andy Turner · Accepted Answer · 2017-12-17 18:30:39Z

2

You know how many elements there will be in the array: two times numbercount, plus 1. So just build that array:

long[] values = new long[2*numbercount+1];
for (int a = 0; a < numbercount; ++a) {
  values[2*a+0] = 100;
  values[2*a+1] = value;
}
values[values.length-1] = 100;

There is no need to involve StringBuilder at all.

answered Dec 17, 2017 at 18:30

Andy Turner

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Comments

Sergey Emeliyanov · Accepted Answer · 2017-12-17 17:24:26Z

0

Your 'longstringbuilder' reference contains nothing but a String with numbers, commas and spaces. You can parse a String which is %100 number, but in your case you have commas and spaces too.

There are several workarounds, for example you could split the String: String[] stringArray = longstringbuilder.split(", "); and then you can parse each item of your stringArray, since it will contain only numeric values.

answered Dec 17, 2017 at 17:24

Sergey Emeliyanov

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Comments

Mureinik · Accepted Answer · 2017-12-17 17:27:10Z

0

Using a StringBuilder looks like the long way round. Using a Stream would be much simpler:

protected long[] getpattern(int numbercount, int value) {
    return IntStream.range(0, numbercount).mapToLong(i -> value).toArray();
}

answered Dec 17, 2017 at 17:27

Mureinik

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3 Comments

Jon Skeet Over a year ago

Or if the OP isn't comfortable with that, just constructing the array and populating it with a for loop would be really, really simple.

Mureinik Over a year ago

I'm surprised there isn't a Winter Bash hat for getting a comment from @JonSkeet :-)

Mureinik Over a year ago

Also, one-liner FTW!

atomSmasher · Accepted Answer · 2017-12-17 17:28:18Z

0

You need to get rid of the commas and spaces in your string. I am using trim in this example but you could probably just split on ", ".

protected long[] getpattern(int numbercount, int value) {
    StringBuilder longstringbuilder = new StringBuilder();

    while(numbercount > 0) {
        longstringbuilder.append("100, ");
        longstringbuilder.append(value + ", ");
        numbercount--;
    }
    longstringbuilder.append("100");

    String longstring = longstringbuilder.toString();
    String[] tokens = longstring.split(",");
    long[] pattern = new long[tokens.length];

    for (int i = 0; i < tokens.length; i++) {
        pattern[i] = Long.parseLong(tokens[i].trim());
    }

    return pattern;
}

answered Dec 17, 2017 at 17:28

atomSmasher

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1 Comment

Julian Zienert Over a year ago

This works fine, because there should be a 100 between every other value. Therefore twice as much numbers

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