Why would the StringBuffer have a limit on its size?
I went through some of the links : http://www.coderanch.com/t/540346/java/java/maximum-size-hold-String-buffer.
Is that because of the count member variable, which is an int?
Suppose that we have 2^31-1 chars in StringBuffer and that we append some more chars to that StringBuffer. Count member variable would be incremented by the number of chars appended and if Count variable is already at its max (2^31-1), it would revert back to some negative value.
Why would it throw an error?
because stringbuffer internally uses an array and the maximum number of elements an array can accommodate is 2^31-1 if you increment after reaching this it will go to negative and throws the error
StringBuffer uses a char[].
In Java an array can be indexed only via an integer which means the highest value the index of the array can be is Integer.MAX_VALUE - 1 (i.e. 2^31 - 1). Which means that the size of an array in Java can not be larger than Integer.MAX_VALUE
Answer is different based on System architecture.
This old machine when I posted answer on 2012
Max Length of characters = 37748734
Java Version : 1.6.0_35
OS : Windows 7
System Architecture : 32bits (x86)
RAM : 2 GB
Processor : Pentium Dual Core E5800 3.20GHz
On 2016
Max Length of characters = 301989886
Java Version : 1.8
OS : Ubuntu 14 LTE and Windows 7
System Architecture : 64bits (x86_64)
RAM : 8 GB
Processor : Intel(R) Core(TM) i3-4130 CPU @ 3.40GHz
Run This program your self
StringBuffer strbTest = new StringBuffer();
long len = 0;
try {
System.out.println("Wait.... til number not generated.");
while(true) {
strbTest.append("a");
len++;
}
} catch (OutOfMemoryError e) {
System.out.println("Max length on your system is "+len);
System.out.println("Error");
}
System.out.println("End");
Output
Max length on your system is 37748734
if you are getting anywhere near 2^31 characters in your buffer you are doing it wrong and you would have run out of memory long ago.
来源：https://stackoverflow.com/questions/11908665/max-size-for-stringbuffer