Java Strings are Immutable - Here's What That Actually Means

Java String are Immutable - but what does that really mean?
We'll learn why Strings are immutable in Java, and what it means for your Java programs.

String immutability in Java means that String objects cannot be modified after they're created. Let's talk about why it matters that Strings are immutable, and why Java chose to make them immutable in this beginner video lesson tutorial.

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Hi, I'm John! I'm a Lead Java Software Engineer and I've been in the programming industry for more than a decade. I love sharing what I've learned over the years in a way that's understandable for all levels of Java learners.

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[etainad]

Hey John! I do not leave comments often, so this is a special event. I am currently learning Java at university and at home, and I wanted to tell you how much your videos are helping me. Your simple way of teaching is amazing for new learners, and I find your channel criminally underrated. Keep on uploading, Im sure youll get big on YouTube, a 100%!

[MrYourSalvation]

Plus one interesting thing - due to String's immutability and presense of a string pool - the hashCode() method is calculated only the first time and saved as a value inside String object. Therefore when you call hashCode() method second time (e.g. on another variable with the same literal value) - it will just return stored value, no need to calculate hash code again.

[mohitsanghai]

Thanks a lot for the crisp and clear video, John. Just to summarize String Immutability Benefits -
1) Usage of String pool, saving tons of memory and hashCode calculation
2) safe for multithreading
3) Removes any security threat by not allowing hackers to change referenced string values to cause security issues in the application

[alexz]

I always had a question about this topic. I read in a book about java, that strings were immutable, but it never went so much into detail. This is a very good video. Thanks for sharing.

[NuanDaa]

Dude I’m in bootcamp now for 6 months and no coding background. I just watched your video and I can say you have a best teaching technique that super understandable. You just got a subscriber. Thanks.

[swapode]

I think you're kinda missing the main reason why Strings are immutable: You can't really have sensible mutable Strings since you can't change their length without moving everything to newly allocated memory on the heap which is incredibly expensive.

I absolutely see your points as benefits, in fact I think Rust has proven that the whole mutable by default approach is a mistake, but it might have been a good idea to go into the actual reason a bit.

[matthewharrison]

You have a talent for explaining things in a concise and easy to process manner. Thank you, sir!

[Hufsa]

first time in this channel and it's absolutely great to dedicate a specific video to talk only about immutable objects in less than 10 minutes, perfectly clear!

[Fadhelalmalki]

I can swear this man is really a man and know how I think giving the needed answer

[misspotato]

I'm self teaching Java currently, I have a lot of questions about the "whys" and "hows" but currently the JavaDocs are a bit too advanced for me. This really helped!

[jiro.nemo.]

Ive been using Java as a student for nearly 5 years now, and your content has been completely mind-blowing to me. Made me adopt the "I know nothing" attitude and relearn everything.

[haoshecn]

Hi, John. Love your tutorials, but I think there is a little thing you didn’t explain in details here. When you new a string “John”, the object is indeed created in the heap, but “John” is still crated inside string pool. There is a reference inside the object pointing towards “John”. So, you actually created two objects when you use ‘new’ keyword to create a string.

[rahulshetty]

Never even used Java a lot but I have been asked this question in interview. But this is the first time I understood what I was telling the interviewer.

[zishanamin]

Protect this man at all costs. Best explanations on Java concepts on the internet

[anluong]

Thanks so much. I've just come up with an interview question about this subject this morning. Luckily I watched your video the night before :)

[rhitamdutta]

Holy shit the way you explain things is so simple and lucid, subbed!!!

[praveenist]

I think I'll never look back again at why string is immutable, you made it super clear 👌🙏 awesome!!!!

[sourav]

This is the best explanation of Immutability on youtube
You are a gem 💎

[abolfazlsaravani]

God I love Java, after 5 years of Java programming, I still love how it works.

[SuprousOxide]

Strings are also very commonly used as keys in Map collections. If you insert a value in a map with a key, and then change the key object, you will no longer be able to look up that value with the original key. And with some map types, may have trouble looking up other keys because you have a key stored in the wrong place.