String vs. StringBuffer in Java: Key Differences & When to Use
String is an immutable sequence of characters in Java; once created, its content never changes. StringBuffer is a mutable sequence that can be modified in place—characters can be appended, inserted, or deleted without creating new objects.
Developers often grab String for everything because it feels familiar, then wonder why concatenation in loops slows apps or spikes memory. The confusion comes from the syntax similarity and the word “string” itself; instinct rarely shouts “mutability matters.”
Key Differences
String: immutable, thread-safe by design, fast for reads, slow for repeated edits. StringBuffer: mutable, synchronized, slightly slower due to locks, ideal for dynamic text building. Memory footprint: String creates new objects on every change; StringBuffer reuses the same buffer.
Which One Should You Choose?
Choose String for constants, configuration keys, or any text that won’t change. Pick StringBuffer when multiple threads may update shared text safely, like logging in web servers. If only a single thread will mutate it, prefer StringBuilder (non-synchronized) for speed.
Examples and Daily Life
Imagine building a tweet: String is perfect for the final 280 characters you post. StringBuffer is the draft where hashtags, mentions, and edits keep flowing in until you hit “publish.”
Does StringBuffer make my code faster?
Inside tight loops, yes—fewer temporary objects mean less garbage collection.
Can I convert between String and StringBuffer?
Absolutely: new String(stringBuffer) or new StringBuffer(string) moves data without altering the original.