.OutOfMemoryError: Java heap space [duplicate]

Question

I want to repeat string 's' and get a large string which has 'n' characters, and want to find how many 'a's in the large string. My code is below and it gives me "OutOfMemoryError: Java heap space" Error and couldn't find a solution for this problem

 String s = "abcab"; long n = 1000000000000l; int strLength = s.length(); double temp = n / strLength; long tempTwo = (long) temp + 1; long countOfAs = 0; // making large String StringBuilder sb = new StringBuilder(s); for (long i = 0; i < tempTwo; i++) { sb.append(s); } //take the sub string which's length is n String out = sb.substring(0, (int) n); //Find 'a's in the sub string char[] stringToCharArray = out.toCharArray(); for (int i = 0; i < n; i++) { if (stringToCharArray[i] == 'a') { countOfAs += 1; } } System.out.println(countOfAs + ">>>>");

You try to build a string with a length of 1.000.000.000.000 characters, which would result in 2.000.000.000.000 bytes. That's 2 TB of data. You don't think that might be a problem? — Progman
– Progman, Commented Oct 31, 2020 at 12:51

Elmar Brauch · Accepted Answer · 2020-10-31 12:59:18Z

Here you can see how to increase Heap size in Java:
Increase heap size in Java

There are easier ways to calculate the a's in your String, it is just:
countOfAs = n * 2;

Your code is wrong, because 2nd for loop must be "i < s.length() * n", because your String has more than one character.

If your String is really the size of 2 TB as commented by @Progman then you should think about an algorithm, which computes countOfAs in several intervals.

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