The String pool is a set of String objects stored in the Permanent Generation section of the heap. Under the hood, an instance of the String class is an array of chars. Each char allocates two bytes. The String class also has a cached hash that allocates four bytes, and each object has housekeeping information that allocates about eight bytes. And if we're talking about Java Development Kit 7 (http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/java/lang/String.java?av=f) or lower, the String class also has offset and length fields. Since String is the most used type, the instances of the String class allocate a significant part of the heap.
To reduce the load on memory, the JVM has the String pool as ...
