Why can holding a substring or splitting large strings cause memory issues, and how do you avoid related leaks?

In old JDKs (pre-7u6) substring() shared the parent's backing char array, so keeping a tiny substring pinned a huge string in memory; modern substring copies, so that specific leak is gone but copying has its own cost.

The current pitfall is splitting or interning huge inputs at scale, which inflates the heap and string pool. For very large text, prefer streaming/CharSequence views, process in chunks, and avoid interning attacker-controlled strings, which can exhaust the pool.