Trying to understand Java String implementation

I'm looking at the openjdk implementation of String and the private, per instance members look like:

public final class String
    implements java.io.Serializable, Comparable<String>, CharSequence
{
    /** The value is used for character storage. */
    private final char value[];

    /** The offset is the first index of the storage that is used. */
    private final int offset;

    /** The count is the number of characters in the String. */
    private final int count;

    /** Cache the hash code for the string */
    private int hash; // Default to 0

    [...]
}

But I know that Java uses reference and pools for Strings, to avoid duplication. I was naively expecting a pimpl idiom, where String would in fact be just a ref to an impl. I'm not seeing that so far. Can someone explain how Java will know to use references if I put a String x; member in one of my classes?

Addendum: this is probably wrong, but if I'm in 32 bits mode, should I count: 4 bytes for the reference "value[]", 4 bytes for offset, 4 for count and 4 for hash for everything instance of class String? That would mean that writing "String x;" in one of my class automatically adds at least 32 bytes to the "weight" of my class (I'm probably wrong here).