package strings; /** * String and StringBuilder's difference are highlighted * - Concatenation create new object in String, but not in StringBuilder * - String methods' return value must be used, otherwise new value is lost */ public class StringVsStringBuilder { public static void main(String[] args) { ///////////////////////////////////////////// // Difference 1: ///////////////////////////////////////////// // Immutable class, create 27 new objects, garbage collector works busy to clean them String str = ""; for (char c='a'; c <= 'z'; c++) str += c; // Mutable class, create only 1 object StringBuilder sb = new StringBuilder(); for (char c='a'; c <= 'z'; c++) sb.append(c); ///////////////////////////////////////////// // Difference 2: ///////////////////////////////////////////// // Immutable class method(i.e. concat) returns reference of newly concatenated String a = "ab"; a = a.concat("cd"); // abcd // while Mutable class method(i.e. append) returns reference of the same object changed StringBuilder b = new StringBuilder("ab"); b.append("cd"); // abcd b.append(true); // abcdtrue b.append(5); // abcdtrue5 b.append((String)null); // requires explicit cast b.append((StringBuilder)null); // requires explicit cast // RESULT: abcdtrue5nullnull // Similarity is method chaining which can be done on both String st = " abc ".trim().toUpperCase().concat("D").substring(2); // CD StringBuilder sbr = new StringBuilder().append("ABC").reverse(); // CBA } }