Java · Theory

Difference between String and StringBuffer

Theory

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Difference between String and StringBuffer

String is immutable: once created, the characters do not change. toUpperCase() returns a new String. The old one stays the same. That is why the String Pool can safely reuse literals.

Immutability also helps security (passwords, class names) and hashing (a String used as a HashMap key cannot silently change).

If you need to change text many times, use StringBuilder. Don’t fight String by concatenating in a loop.

Let's take this on the board with one tiny Main class — no extra files. Difference between String and StringBuffer — same append idea as Builder, but synchronized. Start from main, go line by line, and stop at each print. That output is the proof for Difference between String and StringBuffer.

Exam tip

Buffer = thread-safe builder.

Example

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

Difference between String and StringBuffer — same append idea as Builder, but synchronized.

Short notes

DefString is immutable. Methods return a new String.
RulePool can reuse literals because content never changes.
RememberSafer for HashMap keys and for security.
UseMany changes → StringBuilder, not String + in a loop.

Java · Theory

Difference between String and StringBuffer

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Theory

81/270

Difference between String and StringBuffer

String is immutable: once created, the characters do not change. toUpperCase() returns a new String. The old one stays the same. That is why the String Pool can safely reuse literals.

Immutability also helps security (passwords, class names) and hashing (a String used as a HashMap key cannot silently change).

If you need to change text many times, use StringBuilder. Don’t fight String by concatenating in a loop.

Exam tip

Buffer = thread-safe builder.

Example

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

Difference between String and StringBuffer — same append idea as Builder, but synchronized.

Short notes

DefString is immutable. Methods return a new String.
RulePool can reuse literals because content never changes.
RememberSafer for HashMap keys and for security.
UseMany changes → StringBuilder, not String + in a loop.

Difference between String and StringBuffer

Example

Short notes

Questions

Difference between String and StringBuffer

Example

Short notes

Questions