StringBuffer vs StringBuilder

1. Introduction

In Java, both StringBuffer and StringBuilder are mutable classes that allow you to modify strings without creating new objects each time. They are designed to handle situations where frequent changes to strings are necessary, making them more efficient than the immutable String class.

However, the main difference between StringBuffer and StringBuilder lies in thread safety. While both classes are used for efficiently manipulating strings, StringBuffer is thread-safe (synchronized), and StringBuilder is not thread-safe.

This lecture will explain the differences, use cases, and performance considerations of both classes.

2. StringBuffer vs StringBuilder: Key Differences

3. StringBuffer: Thread-Safe String Manipulation

StringBuffer is a thread-safe class, which means that its methods are synchronized, ensuring that multiple threads can safely modify a StringBuffer instance concurrently without causing data inconsistency.

Example of StringBuffer:

StringBuffer sb = new StringBuffer("Hello");
sb.append(" World");
System.out.println(sb);  // Output: Hello World

In the above example, the append() method modifies the existing StringBuffer object by appending " World". The string is modified in place, and no new object is created.

Use Case: Multi-threaded Environment

StringBuffer is primarily used when you need to perform string manipulations in a multi-threaded environment where the integrity of the string data must be maintained across threads.

4. StringBuilder: Faster String Manipulation

StringBuilder is similar to StringBuffer, but it is not thread-safe. It is more efficient in environments where thread safety is not required because it does not incur the overhead of synchronization.

Example of StringBuilder:

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb);  // Output: Hello World

The StringBuilder works in the same way as StringBuffer, but since it is not synchronized, it is faster when used in single-threaded environments or when thread safety is not a concern.

Use Case: Single-threaded Environment

StringBuilder is ideal for cases where strings are modified frequently in a single-threaded environment, as it offers better performance by avoiding the cost of synchronization.

5. Performance Comparison: StringBuffer vs StringBuilder

Since StringBuffer is thread-safe, it has a slight performance overhead due to synchronization, especially in environments with a high number of concurrent threads.

On the other hand, StringBuilder does not synchronize its methods, making it faster than StringBuffer in single-threaded environments or when thread safety is not needed.

Performance Example:

long startTime = System.nanoTime();
StringBuffer sbf = new StringBuffer("Hello");
for (int i = 0; i < 100000; i++) {
    sbf.append(" World");
}
long endTime = System.nanoTime();
System.out.println("StringBuffer time: " + (endTime - startTime));

startTime = System.nanoTime();
StringBuilder sbl = new StringBuilder("Hello");
for (int i = 0; i < 100000; i++) {
    sbl.append(" World");
}
endTime = System.nanoTime();
System.out.println("StringBuilder time: " + (endTime - startTime));

In this case, StringBuilder will likely perform better due to its lack of synchronization.

6. Methods in StringBuffer and StringBuilder

Both StringBuffer and StringBuilder share the same core set of methods for string manipulation:

• append(): Appends data to the string.
• insert(): Inserts data at a specific index.
• delete(): Removes characters from the string.
• replace(): Replaces a portion of the string with new content.
• reverse(): Reverses the string.
• toString(): Converts the StringBuffer or StringBuilder to a String.

Example:

StringBuffer sb = new StringBuffer("Hello");
sb.insert(5, " World");
sb.reverse();
System.out.println(sb);  // Output: dlroW olleH

Note:

Although the methods are the same, StringBuffer methods are synchronized (thread-safe), while StringBuilder methods are not (not thread-safe).

7. Choosing Between StringBuffer and StringBuilder

You should choose StringBuffer or StringBuilder based on the thread-safety requirement of your program:

• Use StringBuffer when you need thread safety in a multi-threaded environment. For example, when multiple threads are manipulating the same string data, StringBuffer ensures that no data inconsistency occurs.

• Use StringBuilder when performance is a priority, and thread safety is not a concern (such as in a single-threaded environment or when you are certain that no other threads will modify the same string object).

8. Common Mistakes

8.1 Using StringBuffer when performance is critical

If your application is single-threaded, using StringBuffer is inefficient because of the synchronization overhead. In such cases, StringBuilder should be preferred for better performance.

8.2 Ignoring thread-safety when needed

If you are working in a multi-threaded environment and share mutable objects like StringBuilder between threads, you might run into issues where one thread modifies the object while another thread reads it, leading to data corruption. Always use StringBuffer in such cases.

9. Summary

• StringBuffer is thread-safe but slower due to synchronization, making it ideal for multi-threaded environments.
• StringBuilder is not thread-safe but faster, making it suitable for single-threaded environments.
• Both StringBuffer and StringBuilder offer the same methods for manipulating strings but differ in thread safety and performance.
• Always choose StringBuffer when thread safety is required, and StringBuilder when performance is the priority in single-threaded applications.

Written By: Shiva Srivastava