Take out part of a char array and turn it into a string - Java

Question

In Java, is there a premade method that I can use to take some selected indices of an array of chars, stick the terms defined by those indices together and return it as a string? The reason I'm looking for a method here is that I would like to avoid having to create another array to hold my selected values. What I'm looking for is something that looks like this:

public String charArrayToString(char[] array, int startingIndex, int lastIndex) {
        // ignore any index that is outside of the startingIndex - lastIndex range
        // turn array[startingIndex], array[startingIndex + 1] ... array[lastIndex] into a string
}

Peter Lawrey · Accepted Answer · 2012-08-21 13:29:01Z

8

I would use the constructor

public String charArrayToString(char[] array, int startingIndex, int lastIndex) {
    return new String(array, startIndex, lastIndex - startIndex + 1);
}

Depending on what you are doing with the result, a better solution might be to use StringBuilder.append

char[] coords = "000175001022".toCharArray();

StringBuilder sb = new StringBuilder();
sb.append("( ");
sb.append(coords, 0, 6);
sb.append(", ");
sb.append(coords, 6, 6);
sb.append(" )");
System.out.println(sb); // prints ( 000175, 001022 )

edited Aug 21, 2012 at 13:29

answered Aug 21, 2012 at 13:22

Peter Lawrey

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1 Comment

Jon Skeet Over a year ago

I think you need a +1 here as the question appears to want to include lastIndex.

Jon Skeet · Accepted Answer · 2012-08-21 13:21:25Z

7

Sounds like you want:

return new String(array, startingIndex, lastIndex + 1 - startingIndex);

... having done some bounds checks on startingIndex and lastIndex, e.g.

startingIndex = Math.max(startingIndex, 0);
lastIndex = Math.min(lastIndex, array.length - 1);
if (startingIndex > lastIndex) {
    // Return empty string? Throw an exception?
}
return new String(array, startingIndex, lastIndex + 1 - startingIndex);

Note that if you made your upper bound exclusive instead - as most Java APIs are - you could get rid of a lot of these +1 and -1 bits.

answered Aug 21, 2012 at 13:21

Jon Skeet

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3 Comments

Peter Lawrey Over a year ago

The last parameter is the count, rather than the end like substring ;)

Jon Skeet Over a year ago

@AmitD: I prefer to validate the arguments within the methods themselves, as then you can give clearer messages. But yes.

Amit Deshpande Over a year ago

I guess this If would be sufficient same check from new String method -

if (startingIndex >= 0 && 0 <= lastIndex && lastIndex <= array.length - startingIndex) {return string} else{return error }

Amit Deshpande · Accepted Answer · 2012-08-21 13:23:06Z

0

public StringBuilder append(char str[], int offset, int len) {

answered Aug 21, 2012 at 13:23

Amit Deshpande

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4 Comments

Peter Lawrey Over a year ago

Can you add an example of how you would use this method?

Peter Lawrey Over a year ago

This would be the best option if the OP wants to add the result to a string.

Amit Deshpande Over a year ago

@PeterLawrey: Now who cares Jon Skeet has answered the question :)

Peter Lawrey Over a year ago

Jon Skeet often answers questions, but you can still get some reputation. ;)

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