expandCapacity method in AbstractStringBuilder class

Question

I was looking through the source code of this class and I start from append method that is called by StringBUffer.append();

public AbstractStringBuilder append(String str) { if (str == null) str = "null"; int len = str.length(); if (len == 0) return this; int newCount = count + len; if (newCount > value.length) expandCapacity(newCount); // newcount is the new volumn of a char array str.getChars(0, len, value, count); count = newCount; return this; }

Then I went deeper into enpandCapacity method

void expandCapacity(int minimumCapacity) { int newCapacity = (value.length + 1) * 2; //here value is a char array if (newCapacity < 0) { // Why is newCapacity less than 0? // Is that possible? When it will be possible? newCapacity = Integer.MAX_VALUE; } else if (minimumCapacity > newCapacity) { newCapacity = minimumCapacity; } value = Arrays.copyOf(value, newCapacity); }

Why is newCapacity less than 0? Is that possible? When it will be possible?

It's called arithmetic overflow. Signed integers in Java overflow such that MAX_VALUE + 1 == MIN_VALUE — obataku
– obataku, Commented Sep 5, 2012 at 3:21
Take for example Integer.MAX_VALUE * 2, which evaluates to -2. — obataku
– obataku, Commented Sep 5, 2012 at 3:24

Community · Accepted Answer · 2017-05-23 12:21:43Z

Yes; signed integers can become negative once the max value of the int type (2^31 - 1) is exceeded. If you take a look, they are essentially capping the capacity at Integer.MAX_VALUE. Similar type of question here.

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