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Accessor Methods

Getting the Length of a String or a String Buffer

Methods used to obtain information about an object are known as accessor methods. One accessor method that you can use with both strings and string buffers is the length method, which returns the number of characters contained in the string or the string buffer. After the following two lines of code have been executed, len equals 17:

String palindrome = "Dot saw I was Tod";
int len = palindrome.length();

In addition to length, the StringBuffer class has a method called capacity, which returns the amount of space allocated for the string buffer rather than the amount of space used. For example, the capacity of the string buffer referred to by dest in the StringsDemo program never changes, although its length increases by 1 for each iteration of the loop. The following figure shows the capacity and the length of dest after nine characters have been appended to it.

A string buffer's length is the number of characters it contains; a string buffer's capacity is the number of character spaces that have been allocated. The String class doesn't have a capacity method, because a string cannot change.

Getting Characters by Index from a String or a String Buffer

You can get the character at a particular index within a string or a string buffer by using the charAt accessor. The index of the first character is 0; the index of the last is length()-1. For example, the following code gets the character at index 9 in a string:

String anotherPalindrome = "Niagara. O roar again!"; 
char aChar = anotherPalindrome.charAt(9);

Indices begin at 0, so the character at index 9 is 'O', as illustrated in the following figure:

Use the charAt method to get a character at a particular index. The figure also shows that to compute the index of the last character of a string, you have to subtract 1 from the value returned by the length method.

If you want to get more than one character from a string or a string buffer, you can use the substring method. The substring method has two versions, as shown in the following table:

The following code gets from the Niagara palindrome the substring that extends from index 11 to index 15, which is the word "roar":

String anotherPalindrome = "Niagara. O roar again!"; 
String roar = anotherPalindrome.substring(11, 15); 

Use the substring method to get part of a string or string buffer. Remember that indices begin at 0.

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