Take a portion of an array in Java

Question

So I have a string of chars which I want to cycle through in a for loop. When I reach a certain char that passes a boolean check, I want to take every item in the list after that point and cut off from there. Like below:

for (int i = 0; i < charList.length; i++)
{   if (charList[i] == "a")
    {
        //put every char in charList between i and the end into a new variable
    }
}

What ways are there to do this? Which ones are recommended?

What's wrong with what you have? indexOf could work on a substring, which might be better. Not sure about Big-Oh performance. — duffymo, Mar 25 '14 at 15:39
Look for the `copyOfRange` method: http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html — Tyler, Mar 25 '14 at 15:39
The for and if checks are fine. It's the commented part that I don't know how to do. — Sam Ofloinn, Mar 25 '14 at 15:39
Your `if` should be comparing to `'a'` not `"a"` (`char` versus `String`). — 2rs2ts, Mar 25 '14 at 15:49

C.B. · Answer 1 · 2014-03-25T15:46:07.787

3

The Arrays collection has a copyOfRange() method

for (int i = 0; i < charList.length; i++)
{   if (charList[i] == 'a')
    {
        char[] newCharList = Arrays.copyOfRange(charList,i,charList.length);//put every char in charList between i and the end into a new variable
        //do stuff
        break;
    }
}

If you need to access the new array outside the for loop, make sure to declare it before entering, i.e.

char[] newCharList;
for(...

edited Mar 25 '14 at 15:46

answered Mar 25 '14 at 15:40

C.B.

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I think the homework is to create a method that accomplish this. – Luiggi Mendoza Mar 25 '14 at 15:41
1

shouldn't you exit the loop also? – Sionnach733 Mar 25 '14 at 15:42
This is what I was looking for, thank you! @Luiggi Mendoza, this isn't homework; I just tried doing a programming challenge and got caught by the syntax. Thanks anyway! – Sam Ofloinn Mar 25 '14 at 15:44
@SamOfloinn then please specify it's not homework. Also, the variable should be declared outside to be used outsite the `for` loop. – Luiggi Mendoza Mar 25 '14 at 15:48

2rs2ts · Answer 2 · 2014-03-25T15:50:46.780

1

In your if, create a new char[] and then place the characters into it.

char[] substr = new char[charList.length-i];
for (int j = 0; j < charList.length-i; j++) {
    substr[j] = charList[i+j];
}
break; // out of the loop over i

I wrote break but you will probably be returning it, or you would declare substr outside of this scope. The code I wrote is just to give you the idea.

I made a simple ideone for this so you can see it working.

edited Mar 25 '14 at 15:50

answered Mar 25 '14 at 15:44

2rs2ts

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I think you need to specify this code goes inside the `if` posted by OP. – Luiggi Mendoza Mar 25 '14 at 15:47

score 0 · Answer 3 · answered Mar 25 '14 at 15:42

0

Use the copyOfRange() method:

char[] charListCopy = Arrays.copyOfRange(charList, i, charList.size());

answered Mar 25 '14 at 15:42

suavidas

105
3

Take a portion of an array in Java

3 Answers3