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StringBuffer vs StringBuilder in Java

Theory

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StringBuffer vs StringBuilder in Java

Both are mutable text builders. StringBuffer methods are synchronized — thread-safe, slower. StringBuilder is not synchronized — faster, one thread.

Student programs almost always want StringBuilder. Pick StringBuffer only if two threads share the same buffer.

String itself is immutable. Don’t confuse all three.

Let's take this on the board with one tiny Main class — no extra files. StringBuffer vs StringBuilder in Java — output: Hi Java. append changes the same StringBuilder — not a new String each time. Start from main, go line by line, and stop at each print. That output is the proof for StringBuffer vs StringBuilder.

Exam tip

Builder for one thread. Buffer if shared. String cannot change.

Example

// StringBuilder demo
public class Main {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("Hi");
    sb.append(" Java");
    System.out.println(sb.toString());
  }
}

StringBuffer vs StringBuilder in Java — output: Hi Java. append changes the same StringBuilder — not a new String each time.

Short notes

DefBoth mutable builders. Buffer = synced. Builder = faster, one thread.
RuleDefault StringBuilder. Buffer only if shared across threads.
DiffString is immutable. These two can change.
TrapUsing Buffer “because it sounds official” in a single-thread program.

// StringBuilder demo public class Main { public static void main(String[] args) { StringBuilder sb = new StringBuilder("Hi"); sb.append(" Java"); System.out.println(sb.toString()); } }

StringBuffer vs StringBuilder in Java

Example

Short notes

Questions

StringBuffer vs StringBuilder in Java

Example

Short notes

Questions