A string is an ordered sequence of characters, usually stored as bytes that encode text. In many languages it behaves like a read-only array of characters that you can index and iterate over.
Immutability means that once a string is created, its contents never change. Operations that look like edits, such as replacing a character, build a brand new string and leave the original untouched.
Languages make this choice for safety and speed. Immutable strings can be shared freely between threads with no locking, and their hash code can be computed once and reused. The tradeoff is that heavy in-place editing wastes work creating copies. That is why building text in a loop should use a string builder instead.
Rewriting in plainer words…
This answer doesn't lend itself to a diagram - it reads best . No credits were charged.
A string is an ordered sequence of characters, stored as bytes that encode text, and you can index and iterate over it like a read-only array.
Immutable means that once a string is created, its contents never change.
Anything that looks like an edit, say replacing one character, builds a brand new string and leaves the original alone.
Languages pick this for safety and speed, since threads can share a string with no locking and its hash code is computed once and reused.
The cost is a fresh copy on every edit, so when I build text in a loop I use a string builder instead.
Weak answers to avoid
Claims replace or += edits the string in placeThat is the exact misconception the question tests. Say that each edit returns a new string and the original stays untouched.
Says 'it's safer' with no mechanismVague safety claims cost points. Name what immutability buys, such as sharing across threads with no locks and a hash code computed once.
Presents immutability as freeEvery edit builds a copy, so += in a loop gets slow. Name that cost and the fix, a string builder.
Interview lens
Likely follow-ups, what you can say, and the weak answers to avoid.
