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"Hello" strings

 
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All:
Here's some code:


Here is the result of running this code:
Hello
Hello = Hello
true
false

I'm just simply looking for confirmation of my reason why I think line 4 printed "false". I"m thinking it has something to do with immutable String objects, and because the following is true (from K&B SCJP 6, page 430 431)


I'm thinking that on line 1 the println statement resulted in a concatenation of the two string objects in order to complete the println command, however this same oncatenation does not happen in the code on line 4. Is this true? And if true, what will the JVM in fact be comparing the hello String object to, will it be the "Hel" character string alone or the lo String object alone, or something else?

Thank you for your time.
Gary
 
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The simple answer is that on string concatenation, a new String object is created, so it is in a different location on the memory, so it wont be "==" to the old String, but only "equals".
 
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Ajezi Sajirava wrote:The simple answer is that on string concatenation, a new String object is created, so it is in a different location on the memory, so it wont be "==" to the old String, but only "equals".




Agreed. The "simple answer" is to use the equals() method. Any more than that will require knowledge of the string pool and strings as compile time constants.

Henry
 
Gary Marshall
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OK, thank you.

Then why is it that line3 returns "true"? Doesn't the code "..... ("Hel"+"lo"))" create a new String object, and therefore shouldn't the code

System.out.println(hello == ("Hel"+"lo")); also return false?

Thank you
Gary
 
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Line 3 returns true because "Hel" + "lo" ,which finally results in "Hello" , would refer to the existing object in String pool.
Someone please correct me if I am wrong.
 
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String doubt

This question has been discussed here in more detail
 
Henry Wong
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Max White wrote:Line 3 returns true because "Hel" + "lo" ,which finally results in "Hello" , would refer to the existing object in String pool.
Someone please correct me if I am wrong.



Correct. ("Hel" + "lo") is a compile time constant expression, which becomes "Hello", which in turn, shares the same copy due to the string pool.

Henry
 
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Welcome to JavaRanch, Ajezi Sajirava
 
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