String immutability in Java - Cheat Sheet & Quick Revision

overview

Recall & Review

beginner

What does it mean that a String is immutable in Java?

It means once a String object is created, its content cannot be changed. Any modification creates a new String object.

intermediate

Why are Strings designed to be immutable in Java?

Immutability helps with security, thread safety, and performance optimizations like string pooling.

beginner

What happens when you try to change a String using methods like concat() or replace()?

These methods do not change the original String. Instead, they return a new String with the changes.

intermediate

How does String immutability affect memory usage in Java?

Because Strings are immutable, Java can safely share String objects in the string pool, reducing memory use.

beginner

Can you modify the characters inside a String object directly in Java?

No, you cannot change characters inside a String directly because Strings are immutable.

What happens when you call the replace() method on a String in Java?

A A new String is created with the replacements

B The original String is changed

C An error occurs

D The String becomes mutable

Why is String immutability important for thread safety?

A Because immutable objects cannot be changed by multiple threads simultaneously

B Because immutable objects are slower

C Because immutable objects use more memory

D Because immutable objects require synchronization

Which of these is true about Java Strings?

A They are mutable by default

B They can be changed after creation

C They are immutable

D They are only immutable if declared final

What is the benefit of the String pool in Java?

A It stores only mutable Strings

B It makes Strings mutable

C It slows down String creation

D It allows sharing of immutable String objects to save memory

If you want to change characters in a sequence of text efficiently, what should you use instead of String?

A char array

B StringBuilder or StringBuffer

C int array

D HashMap

Explain what String immutability means in Java and why it is useful.

Describe how Java uses the String pool and how immutability makes it possible.