Java char array to String without creating new objects

Question

When creating a String like this:

String s1 = “ABC”

the JVM will look in the String pool if "ABC" exists there and create a new object only if "ABC" doesn't exist yet.

So the usage of

String s1 = new String("ABC")

halts this behavior and will create an object every time.

Now I have a problem when converting a char array to String:

private char[] names;
...
@Override
public String toString() {
  return new String(this.names);
}

This will always create a new object. Can I convert from char array to String without creating a new object each time?

What's your objective? Reduce memory usage, or avoid creating strings/garbage? — ernest_k, Jul 02 '21 at 11:09
If memory is a real concern (e.g. if these are long-living strings), then consider switching on `-XX:+UseStringDeduplication` (IIRC, this requires using G1GC). — Mark Rotteveel, Jul 02 '21 at 14:15
That depends on why you use a `char[]` array in your class instead of just a reusable `String` reference. — Holger, Jul 05 '21 at 11:14

score 2 · Answer 1 · answered Jul 02 '21 at 11:32

I know of no way to avoid creating a String object in your toString(), but you can avoid retaining these new strings (all but the first one become eligible for GC after the method execution) by explicitly calling String.intern():

@Override
public String toString() {
    return new String(this.names).intern();
}

And you can test it by repeatedly checking myObject.toString() == myObject.toString().

But before doing this, do yourself a favor and be aware of what you're doing. It's possible that generating a string object is the better choice, depending on your main reason for doing this.

Java char array to String without creating new objects

1 Answers1