Question

When i was dealing with threads concept in Java, i have seen Thread.java source file. I noticed when setName() method assigns string to a character array called "name[]". Java has a feature of String data type, then why they are using character array.

In source file it is initialised like,

private char name[]; // why not "private String name;"

In setName() method,

public final void setName(String name) {
    checkAccess();
    this.name = name.toCharArray();
    }

Please help me. Thanks in advance.

Answer 1

This name is accessed from native code, so it is easier to handle char arrays than mangle with Java types. The core-lib-devs mailing list discussed this question a while ago, here’s a link to one mail from the thread. The original question stated that “a fair amount of time goes to that Thread.setName call which I believe a significant portion is to do new char allocation and copy char array etc”. Quoting bits of the answer:

There was an RFE for this way back in late 2002:

4745629 (thread) Thread.setName does needless string allocations
(don’t use char[])

The initial eval in 2002 stated:

“I can’t imagine that this seriously impacts the performance of any
real program. Furthermore, changing the fields in Thread is
problematic due to the close relationship of this class with the VM.
That said, it might be worth addressing this in the context of some
Thread code-cleanup.”

Then in 2005 it was closed as “will not fix”:

“There are dependencies on the name representation being a char array
in the JVM and this RFE must be respectfully rejected.”