• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Liutauras Vilda
  • Tim Cooke
  • Paul Clapham
  • Jeanne Boyarsky
Sheriffs:
  • Ron McLeod
  • Frank Carver
  • Junilu Lacar
Saloon Keepers:
  • Stephan van Hulst
  • Tim Moores
  • Tim Holloway
  • Al Hobbs
  • Carey Brown
Bartenders:
  • Piet Souris
  • Frits Walraven
  • fred rosenberger

How does substring () inside String works?

 
Ranch Hand
Posts: 954
4
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I was reading interview questions randomly on different sites and came across this question. They have mentioned that till 1.7 substring
holds reference to the original string. So if you even choose small part of bigger string, it can't be GC. This problem is resolved in 1.7.

I have checked src code for both 1.6 and 1.8 and doesn't find any difference in the implementation. Any idea?
 
Tushar Goel
Ranch Hand
Posts: 954
4
  • Likes 1
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I figured it out. By looking the code closly i found in java-6 same instance of the array keeps but in 1.8 values are copied.
 
Marshal
Posts: 76462
366
  • Likes 1
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
You are right
Pre‑Java7 implementations kept a reference to the whole backing array. If that is much larger than the substring it can cause a memory leak. It was the only instance (I think) where it was worth using the String copy constructor.
String s = myText.substring(123, 456); // Risk of keeping whole backing array
String s = new String(myText.substring(123, 456)); // No risk of memory leak
As you said, since Java7 that trick has been unnecessary.
 
Tushar Goel
Ranch Hand
Posts: 954
4
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
thanks Campbell..
 
Campbell Ritchie
Marshal
Posts: 76462
366
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
You're welcome
 
I love a woman who dresses in stainless steel ... and carries tiny ads:
the value of filler advertising in 2021
https://coderanch.com/t/730886/filler-advertising
reply
    Bookmark Topic Watch Topic
  • New Topic