Re: Why "lock" functionality is introduced for all the objects?

Patricia Shanahan <>
Tue, 28 Jun 2011 12:34:15 -0700
On 6/28/2011 11:54 AM,
supercalifragilisticexpialadiamaticonormalizeringelimatisticantations wrote:

On 28/06/2011 2:42 PM, Patricia Shanahan wrote:

Each String instance has the following fields:

private final char value[];
private final int offset;
private final int count;
private int hash;

There are 12 bytes in addition to the char array. The offset and count
fields allow quick sub-string construction, and hash is used to cache
the hashCode result.

Oh, geez, even *more* overhead. And let's not forget the array has its
own separate object header and length field!

The array may be shared by several String objects.

In general, many trade-offs in Java, not just the decision to make every
object capable of being a lock, assume that other considerations are
more important than minimizing memory use. For example, caching the hash
code pays four bytes per String in order to have a hash code that
depends on the entire string, without paying the cost of calculating it
repeatedly when a String is used as a hash table key.

If, for your purposes, minimal memory use is very important, you may
want to consider other languages with other trade-offs.


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