Difference between StringBuilder and StringBuffer

StringBuffer is synchronized, StringBuilder is not.

Basically, StringBuffer methods are synchronized while StringBuilder are not.

The operations are "almost" the same, but using synchronized methods in a single thread is overkill.

That's pretty much about it.

Quote from StringBuilder API:

This class [StringBuilder] provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

So it was made to substitute it.

The same happened with Vector and ArrayList.

But needed to get the clear difference with the help of an example?

StringBuffer or StringBuilder

Simply use StringBuilder unless you really are trying to share a buffer between threads. StringBuilder is the unsynchronized (less overhead = more efficient) younger brother of the original synchronized StringBuffer class.

StringBuffer came first. Sun was concerned with correctness under all conditions, so they made it synchronized to make it thread-safe just in case.

StringBuilder came later. Most of the uses of StringBuffer were single-thread and unnecessarily paying the cost of the synchronization.

Since StringBuilder is a drop-in replacement for StringBuffer without the synchronization, there would not be differences between any examples.

If you are trying to share between threads, you can use StringBuffer, but consider whether higher-level synchronization is necessary, e.g. perhaps instead of using StringBuffer, should you synchronize the methods that use the StringBuilder.

StringBuilder was introduced in Java 1.5 so it won't work with earlier JVMs.

From the Javadocs:

StringBuilder class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

StringBuffer

• Synchronized hence threadsafe
• Thread safe hence slow

StringBuilder

• Introduced in Java 5.0
• Asynchronous hence fast & efficient
• User explicitly needs to synchronize it, if he wants
• You can replace it with StringBuffer without any other change

StringBuilder is not thread safe. String Buffer is. More info here.

EDIT: As for performance , after hotspot kicks in , StringBuilder is the winner. However , for small iterations , the performance difference is negligible.

The javadoc explains the difference:

This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

Difference between StringBuffer and StringBuilder Source:

StringBuilder (introduced in Java 5) is identical to StringBuffer, except its methods are not synchronized. This means it has better performance than the latter, but the drawback is that it is not thread-safe.

Read tutorial for more details.

Better use StringBuilder since it is not synchronized and offers therefore better performance. StringBuilder is a drop-in replacement of the older StringBuffer.

StringBuffer is used to store character strings that will be changed (String objects cannot be changed). It automatically expands as needed. Related classes: String, CharSequence.

StringBuilder was added in Java 5. It is identical in all respects to StringBuffer except that it is not synchronized, which means that if multiple threads are accessing it at the same time, there could be trouble. For single-threaded programs, the most common case, avoiding the overhead of synchronization makes the StringBuilder very slightly faster.

StringBuffer is synchronized, but StringBuilder is not. As a result, StringBuilder is faster than StringBuffer.

The major difference is StringBuffer is syncronized but StringBuilder is not.If you need to use more than one thread , then StringBuffer is recommended.But, as per the execution speed StringBuilder is faster than StringBuffer , because its not syncronized .

Here is the performance testing result for String vs StringBuffer vs StringBuilder. Finally, StringBuilder won the Test. See below for test code and result.

Code:

private static void performanceTestStringVsStringbuffereVsStringBuilder() {
// String vs StringBiffer vs StringBuilder performance Test

int loop = 100000;
long start = 0;

// String
String str = null;
start = System.currentTimeMillis();
for (int i = 1; i <= loop; i++) {
  str += i + "test";
}
System.out.println("String - " + (System.currentTimeMillis() - start) + " ms");

// String buffer
StringBuffer sbuffer = new StringBuffer();
start = System.currentTimeMillis();
for (int i = 1; i <= loop; i++) {
  sbuffer.append(i).append("test");
}
System.out.println("String Buffer - " + (System.currentTimeMillis() - start) + " ms");

// String builder
start = System.currentTimeMillis();
StringBuilder sbuilder = new StringBuilder();
for (int i = 1; i <= loop; i++) {
  sbuffer.append(i).append("test");
}
System.out.println("String Builder - " + (System.currentTimeMillis() - start) + " ms");

  }

Execute Me on ideone

Result:

100000 iteration for adding a single text

String - 37489 ms
String Buffer - 5 ms
String Builder - 4 ms

10000 iteration for adding a single text

String - 389 ms
String Buffer - 1 ms
String Builder - 1 ms

• StringBuffer is thread-safe but StringBuilder is not thread safe.
• StringBuilder is faster than StringBuffer.
• StringBuffer is synchronized whereas StringBuilder is not synchronized.

Others have rightly pointed out the key differences between the two. However in terms of performance I would like to add that a JVM level optimization "Lock Elision" which could make the performance difference in context of synchronization to be almost non-existent. An excellent read on this is here and here

StringBuilder is faster than StringBuffer because StringBuffer is synchronized, StringBuffer has its own char[] buffer for cache like BufferedInputStream does.

Another reason that StringBuffer is slower is that because every time you append or remove, it will update variable buffer. I tested it, and somehow StringBuffer‘s remove method is faster if I remove more than ten thousand times.