STRINGS - Introduction to Java Programming - page 340

Caution
Attempting to access characters in a string s out of bounds is a common program-
ming error. To avoid it, make sure that you do not use an index beyond
s.length() - 1 . For example, s.charAt(s.length()) would cause a
StringIndexOutOfBoundsException .

string index range

You can use the concat method to concatenate two strings. The statement shown below, for
example, concatenates strings s1 and s2 into s3 :

String s3 = s1.concat(s2);

s1.concat(s2)

Because string concatenation is heavily used in programming, Java provides a convenient way
to accomplish it. You can use the plus ( + ) operator to concatenate two strings, so the previous
statement is equivalent to

String s3 = s1 + s2;

s1 + s2

The following code combines the strings message , " and " , and "HTML" into one string:

String myString = message + " and " + "HTML" ;

Recall that the + operator can also concatenate a number with a string. In this case, the num-
ber is converted into a string and then concatenated. Note that at least one of the operands
must be a string in order for concatenation to take place.

9.2.5 Obtaining Substrings
You can obtain a single character from a string using the charAt method, as shown in Figure 9.3.
You can also obtain a substring from a string using the substring method in the String class,
as shown in Figure 9.5.

For example,

String message = "Welcome to Java" .substring( 0 , 11 ) + "HTML" ;

The string message now becomes Welcome to HTML .

java.lang.String

+substring(beginIndex: int):
String

Returns this string's substring that begins with the character at the
specified beginIndex and extends to the end of the string, as
shown in Figure 9.6.
Returns this string's substring that begins at the specified
beginIndex and extends to the character at index endIndex - 1 ,
as shown in Figure 9.6. Note that the character at endIndex is not
part of the substring.

+substring(beginIndex: int,
endIndex: int): String

F IGURE 9.5

The String class contains the methods for obtaining substrings.

0123456789 0 1 2 3 4
We l

Indices
Message

c om e t o J a v a

message.substring(0, 11) message.substring(11)

F IGURE 9.6

The substring method obtains a substring from a string.