The StringBuilder Class

StringBuilder objects are like String objects, except that they can be modified. Internally, these objects are treated like variable-length arrays that contain a sequence of characters. At any point, the length and content of the sequence can be changed through method invocations.

Strings should always be used unless string builders offer an advantage in terms of simpler code (see the sample program at the end of this section) or better performance. For example, if you need to concatenate a large number of strings, appending to a StringBuilder object is more efficient.
Length and Capacity
The StringBuilder class, like the String class, has a length() method that returns the length of the character sequence in the builder.

Unlike strings, every string builder also has a capacity, the number of character spaces that have been allocated. The capacity, which is returned by the capacity() method, is always greater than or equal to the length (usually greater than) and will automatically expand as necessary to accommodate additions to the string builder.

StringBuilder Constructors Constructor Description
StringBuilder() Creates an empty string builder with a capacity of 16 (16 empty elements).
StringBuilder(CharSequence cs) Constructs a string builder containing the same characters as the specified CharSequence, plus an extra 16 empty elements trailing the CharSequence.
StringBuilder(int initCapacity) Creates an empty string builder with the specified initial capacity.
StringBuilder(String s) Creates a string builder whose value is initialized by the specified string, plus an extra 16 empty elements trailing the string.

For example, the following code

StringBuilder sb = new StringBuilder(); // creates empty builder, capacity 16
sb.append("Greetings"); // adds 9 character string at beginning

will produce a string builder with a length of 9 and a capacity of 16:

A string builder's length is the number of characters it contains; a string builder's

The StringBuild