The String class provides a number of ways in which characters can be extracted from a String object. Although the characters that comprise a string within a String object cannot be indexed as if they were a character array, many of the String methods employ an index (or offset) into the string for their operation. Like arrays, the string indexes begin at zero.

charAt( )

To extract a single character from a String, you can refer directly to an individual character via the charAt( ) method. It has this general form:

char charAt(int where)

Here, where is the index of the character that you want to obtain. The value of where must be nonnegative and specify a location within the string. charAt( ) returns the character at the specified location. For example,

char ch;
ch = "abc".charAt(1);

assigns the value “b” to ch. 

getChars( )

If you need to extract more than one character at a time, you can use the getChars( ) method.

It has this general form:

void getChars(int sourceStart, int sourceEnd, char target[ ], int targetStart)

Here, sourceStart specifies the index of the beginning of the substring, and sourceEnd specifies an index that is one past the end of the desired substring.

Thus, the substring contains the characters from sourceStart through sourceEnd1. The array that will receive the characters – is specified by target.

The index within target at which the substring will be copied is passed in targetStart. Care must be taken to assure that the target array is large
enough to hold the number of characters in the specified substring.

class getCharsDemo {
public static void main(String args[]) {
String s = "This is a demo of the getChars method.";
int start = 10;
int end = 14;
char buf[] = new char[end - start];
s.getChars(start, end, buf, 0);