What is the difference between the String and StringBuffer classes

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String objects are constants. StringBuffer objects are not constants.

In Core Java, the main difference between the String and StringBuffer classes lies in their mutability.

  1. Immutability (String):
    • Strings in Java are immutable, meaning their values cannot be changed once they are assigned.
    • Any operation that appears to modify a String actually creates a new String object.

    Example:

    java
    String str1 = "Hello";
    str1 = str1 + " World"; // This creates a new String object
  2. Mutability (StringBuffer):
    • StringBuffer is mutable, allowing the content of the object to be changed without creating a new object.
    • This can be more efficient when you need to perform a lot of modifications to a string.

    Example:

    java
    StringBuffer stringBuffer = new StringBuffer("Hello");
    stringBuffer.append(" World"); // Modifies the existing StringBuffer object
  3. Performance:
    • Because of the immutability of String, concatenating multiple strings using the + operator can result in the creation of many intermediate String objects, which can impact performance.
    • StringBuffer is more efficient for such operations, especially when dealing with a large number of string modifications.
  4. Thread Safety:
    • String objects are inherently thread-safe because they are immutable. Once created, their values cannot be changed, making them safe for use in a multithreaded environment.
    • StringBuffer is explicitly designed to be thread-safe. It includes synchronized methods to ensure safe concurrent access.

In summary, if you need an immutable sequence of characters, and the value is not going to change frequently, then String is the appropriate choice. If you need a mutable sequence of characters or are frequently modifying the content, then StringBuffer should be used. In modern Java, StringBuilder is often preferred over StringBuffer in situations where thread safety is not a concern, as StringBuilder is not synchronized, providing better performance in single-threaded scenarios.