Strings and Garbage Collection

[Dale DeMott]

Are strings collected in the garbage collection if the original object that created them still exists but no longer references them.
Example
MyObject had a string in it that was
String myString = "Hello";
Later on myString references a different string...
myString = "Good Bye";
Will the "Hello" string be garbage collected when the garbage collector comes along?

-Dale

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By failing to prepare, you are preparing to fail.
Benjamin Franklin (1706 - 1790)

[jason adam]

Since Strings are objects, and objects that no longer have a reference to them are eligible for collection, I would say yes. I haven't read anything that says otherwise.
Jason
[This message has been edited by jason adam (edited November 20, 2001).]

[Dave Vick]

Dale
As far as I know (and someone may correct me if I'm wrong), the two Strings you create in your examples are just Strings stored in the String pool and pool Strings are not subject to Garbage Collection because you haven't actually made an Object. If you had used new to create myString then it would be subject to garbage collection.
hope that helps

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Dave
Sun Certified Programmer for the Java� 2 Platform

[Valentin Crettaz]

I agree with Dave,
only Strings created with the new keyword are subject to garbage collection. Other String, called String literals, are interned in the String pool and not garbage collected.

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Valentin Crettaz
Sun Certified Programmer for Java 2 Platform

[Dale DeMott]

So knowing that, are the strings created with the NEW keyword put into the string pool as well?
-Dale

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By failing to prepare, you are preparing to fail.
Benjamin Franklin (1706 - 1790)

[Gaia Nathan]

If I'm not mistaken Dale, all strings created using the "new" keyword are stored in the heap, just like all other objects.
These strings will be subject to garbage collection should no variable reference them.

[jason adam]

Thanks for the correction on the pool vs. heap. I've unfortunately seen references to this where new was not used to create the String, but instead was something like:
String s = "String" ;
System.out.println( s );
s = null ;
And it was stated that "String" is now eligible for GC. Is this then incorrect?
Jason

[Marilyn de Queiroz]

Yes, it is incorrect.
If you had

String s = new String( "String" );
System.out.println( s );
s = null ;

instead, the statement would be correct.

"When you allocate space for a String using new, that object goes to the heap and is garbage-collectible once it's fully dereferenced. A static String remains in program memory no matter what. Even if you completely dereference it, it's there and will get used again if you re-assign its value. Honest!"

-- Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide

[jason adam]

That's what I get for reading books that aren't on the recommended list
Jason

[Sadaf Zaidi]

Thank you Marily.Nice explanation.

[Ilja Preuss]

Originally posted by Marilyn deQueiroz:
Yes, it is incorrect.
If you had

String s = new String( "String" );
System.out.println( s );
s = null ;

instead, the statement would be correct.

"When you allocate space for a String using new, that object goes to the heap and is garbage-collectible once it's fully dereferenced. A static String remains in program memory no matter what. Even if you completely dereference it, it's there and will get used again if you re-assign its value. Honest!"

-- Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide

Notice that in your example, you have *two* String objects: One created using the new keyword, going to the heap, and the literal one used to create the other (the parameter to the String constructor). So there will be one String in the constant pool and a copy on the heap (until the latter gets gc'ed).