How many string objects this program will create

Question

Below is a Java program.

 public String makinStrings() {
 String s = “Fred”;
 s = s + “47”;
 s = s.substring(2, 5);
 s = s.toUpperCase();
 return s.toString();
 }

How can I find out how many String object is created in the String pool. I think there are 4 objects created which are - "Fred" , "Fred47" , "ed4" , "ED4". Is this correct assumption?

Possible duplicate of How many String objects will be created — xehpuk
– xehpuk, Commented Oct 11, 2015 at 3:30

Community · Accepted Answer · 2017-05-23 12:22:23Z

1

For the Java version 7:

Due to this topic the + operator creates new object
Due to String reference and this topic:
- substring() creates a new string because String is immutable
- toUpperCase() creates a new string because String is immutable
- toString() does not create a new string but returning him itself

Assigning the "Fred" at the beginning won't create a new object since it will be taken from literal pool

To sum up - 3 Strings has been created with every method call. The string is an object so returning it does not create new - it is done by reference.

edited May 23, 2017 at 12:22

CommunityBot

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answered Oct 11, 2015 at 2:50

m.antkowicz

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2 Comments

xehpuk Over a year ago

Why do you think toUpperCase() doesn't create a new string?

m.antkowicz Over a year ago

Of course it will - I've been suggested with no explicit information in the reference what was acually wrong. The question is a duplicate of stackoverflow.com/questions/7370593/… btw but I cannot flag it for some weird reason - I edited answer to the proper one (cause I also cannot delete it now... uhh). Thanks for the warning anyway

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