Java: StringBuilder vs StringBuffer

Both StringBuilder and StringBuffer are used to mutate Strings. These classes also have the same methods so if you were to create a new StringBuffer or StringBuilder object you could use them interchangeably.

StringBuilder

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StringBuilder sb = new StringBuilder();

StringBuffer

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StringBuffer sb = new StringBuffer();

Both sb objects can now be used in the same manner and produce the same result.

Append to String

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sb.append("hello");
sb.append("world");
System.out.println(sb.toString());

Console Output

helloworld

Now if we want to insert a space between hello and world we can use our existing sb object and insert a space at index 5 which is the length of ‘hello’.

Insert into String

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sb.insert(5, " ");
System.out.println(sb.toString());

Console Output

hello world

So should you use StringBuffer or StringBuilder? Generally you should choose StringBuilder because it is faster and was created as a drop-in replacement for StringBuffer.

That’s not all for StringBuffer however, there is still a reason why you may want to use it. All of StringBuffer’s methods are synchronized so it is thread-safe and can be shared among threads.