What happens when a Java String overflows?

Question

As far as I understand, Java Strings are just an array of characters, with the maximum length being an integer value. If I understand this answer correctly, it is possible to cause an overflow with a String - albeit in "unusual circumstances".

Since Java Strings are based on char arrays and Java automatically checks array bounds, buffer overflows are only possible in unusual scenarios:

1. If you call native code via JNI
2. In the JVM itself (usually written in C++)
3. The interpreter or JIT compiler does not work correctly (Java bytecode mandated bounds checks)

Correct me if I'm wrong, but I believe this means that you can write outside the bounds of the array, without triggering the ArrayIndexOutOfBounds (or similar) exception.

I've encountered issues in C++ with buffer overflows, and I can find plenty of advice about other languages, but none specifically answering what would happen if you caused a buffer overflow with a String (or any other array type) in Java.

I know that Java Strings are bounds-checked, and can't be overflowed by native Java code alone (unless issues are present in the compiler or JVM, as per points 2 and 3 above), but the first point implies that it is technically possible to get a char[] into an... undesirable position.

Given this, I have two specific questions about the behaviour of such issues in Java, assuming the above is correct:

1. If a String can overflow, what happens when it does?
2. What would the implications of this behaviour be?

Thanks in advance.

Answer 1

To answer you first question, I had the luck of actually causing a error of such, and the execution just stopped throwing one of these errors:

java.lang.OutOfMemoryError: Requested array size exceeds VM limit

So that was my case, I don't know if that represents a security problem as buffer overflow in C and C++.