These rules deal with different problems that can occur with manipulation of the class String or StringBuffer. Code containing duplicate String literals can usually be improved by declaring the String as a constant field. 3 Avoid instantiating String objects; this is usually unnecessary. 2 Avoid calling toString() on String objects; this is unnecessary. 3 Avoid concatenating non literals in a StringBuffer constructor or append(). 3 Using equalsIgnoreCase() is faster than using toUpperCase/toLowerCase().equals() 3 Use StringBuffer.length() to determine StringBuffer length rather than using StringBuffer.toString().equals("") or StringBuffer.toString().length() ==. 3 Avoid concatenating characters as strings in StringBuffer.append. 3 Consecutively calling StringBuffer.append with String literals 3 Use String.indexOf(char) when checking for the index of a single character; it executes faster. 3 String.trim().length() is an inefficient way to check if a String is really empty, as it creates a new String object just to check its size. Consider creating a static function that loops through a string, checking Character.isWhitespace() on each character and returning false if a non-whitespace character is found. 3 0) { doSomething(); } } } ]]> Failing to pre-size a StringBuffer properly could cause it to re-size many times during runtime. This rule checks the characters that are actually passed into StringBuffer.append(), but represents a best guess "worst case" scenario. An empty StringBuffer constructor initializes the object to 16 characters. This default is assumed if the length of the constructor can not be determined. 3 No need to call String.valueOf to append to a string; just use the valueOf() argument directly. 3 StringBuffer sb = new StringBuffer('c'); The char will be converted into int to intialize StringBuffer size. 4 Using '==' or '!=' to compare strings only works if intern version is used on both sides 3 3