STRINGS - Introduction to Java Programming - page 362

4.

You can use the concat method to concatenate two strings, or the plus ( + ) operator
to concatenate two or more strings.

5.

You can use the substring method to obtain a substring from the string.

6.

You can use the equals and compareTo methods to compare strings. The equals
method returns true if two strings are equal, and false if they are not equal. The
compareTo method returns 0 , a positive integer, or a negative integer, depending on
whether one string is equal to, greater than, or less than the other string.

7.

A regular expression (abbreviated regex ) is a string that describes a pattern for match-
ing a set of strings. You can match, replace, or split a string by specifying a pattern.

8.

The Character class is a wrapper class for a single character. The Character class
provides useful static methods to determine whether a character is a letter
( isLetter(char) ), a digit ( isDigit(char) ), uppercase ( isUpperCase(char) ),
or lowercase ( isLowerCase(char) ).

9.

The StringBuilder and StringBuffer classes can be used to replace the
String class. The String object is immutable, but you can add, insert, or append
new contents into StringBuilder and StringBuffer objects. Use String if the
string contents do not require any change, and use StringBuilder

or

StringBuffer if they might change.

10.

You can pass strings to the main method from the command line. Strings passed to
the main program are stored in args , which is an array of strings. The first string is
represented by args[0] , and args.length is the number of strings passed.

T EST Q UESTIONS

Do the test questions for this chapter online at www.cs.armstrong.edu/liang/intro9e/test.html .

P ROGRAMMING E XERCISES

Sections 9.2-9.3
*9.1

( Check SSN ) Write a program that prompts the user to enter a Social Security
number in the format DDD-DD-DDDD, where D is a digit. The program displays
Valid SSN for a correct Social Security number and Invalid SSN otherwise.

**9.2

( Check substrings ) You can check whether a string is a substring of another string
by using the indexOf method in the String class. Write your own method for
this function. Write a program that prompts the user to enter two strings, and
checks whether the first string is a substring of the second.

**9.3

( Check password ) Some websites impose certain rules for passwords. Write a
method that checks whether a string is a valid password. Suppose the password
rules are as follows:

A password must have at least eight characters.

■

A password consists of only letters and digits.

■

A password must contain at least two digits.
Write a program that prompts the user to enter a password and displays Valid
Password if the rules are followed or Invalid Password otherwise.

■