StringBuilder vs StringBuffer

StringBuilder was introduced in JDK 1.5. What's the difference between StringBuilder and StringBuffer? According to javadoc, StringBuilder is designed as a replacement for StringBuffer in single-threaded usage. Their key differences in simple term:

StringBuffer is designed to be thread-safe and all public methods in StringBuffer are synchronized. StringBuilder does not handle thread-safety issue and none of its methods is synchronized.

StringBuilder has better performance than StringBuffer under most circumstances.

Use the new StringBuilder wherever possible.

Other than that, the two classes are remarkably similar with compatible API. It seems the author just copied StringBuffer.java to StringBuilder.java, removing all occurrences of "synchronized". Here is a little trace left in StringBuilder.readObject method:

/**
* readObject is called to restore the state of the 
* StringBuffer from a stream.
*/
private void readObject(java.io.ObjectInputStream s)

Note the above javadoc still refers to StringBuffer where it should be StringBuilder.
2 interesting methods in StringBuilder or StringBuffer are reverse() and equals(Object):

reverse() method modifies the current this StringBuilder/StringBuffer, and also returns itself. More details in Reverse a String with StringBuilder or StringBuffer

equals(Object) method is not implemented (overridden) in StringBuilder/StringBuffer. So comparing 2 instances of the same content will return false. Also there is no equalsIgnoreCase() method on StringBuilder/StringBuffer. However, toString() is implemented to return a string representing the data in this StringBuilder/StringBuffer.

When writing javadocs, IntelliJ automatically adds a closing tag for html elements. For instance, after typing <lt>, it automaticaly adds </lt>, or after typing <p>, it adds </p>. It can be annoying since simple html elements like those used in javadocs don't really need ending tags.
To disable javadoc automatic closing tags in IntelliJ, simply go to IntelliJ Preferences -> Editor -> Smart Keys, then on the right panel, uncheck Automatically insert closing tag.

Intellij 14 screenshot:

Intellij 15 screenshot:

A related note, JDK 8 has tightened javadoc syntax check, and as a result self-closing elements like <p/>, or <br/> are deemed invalid and will cause failures. See JDK-8020619. However, this checking can be disabled by passing nonstandard option -Xdoclint:none to javadoc tool. For official javadoc guidelines, see How to Write Doc Comments for the Javadoc Tool .

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