Java Reference
In-Depth Information
Character Testing Using Standard Library Methods
While testing characters using logical operators is a useful way of demonstrating how these operators
work, in practice there is an easier way. The standard Java packages provide a range of standard
methods to do the sort of testing for particular sets of characters such as letters or digits that we have
been doing with if statements. They are all available within the class Character , which is
automatically available in your programs. For example, we could have written the if statement in our
LetterCheck program as shown in the following example.
Try It Out - Deciphering Characters Trivially
Replace the code body of the LetterCheck class with the following code:
if(Character.isUpperCase(symbol)) {
System.out.println("You have the capital letter " + symbol);
} else {
if(Character.isLowerCase(symbol)) {
System.out.println("You have the small letter " + symbol);
} else {
System.out.println("The code is not a letter");
}
}
How It Works
The isUpperCase() method returns true if the char value passed to it is uppercase, and false if it is
not. Similarly, the isLowerCase() method returns true if the char value passed to it is lowercase.
The following table shows some of the other methods included in the class Character that you may
find useful for testing characters. In each case the argument to be tested is of type char , and is placed
between the parentheses following the method name:
Method
Description
isDigit()
Returns the value true if the argument is a digit (0 to 9) and false
otherwise.
isLetter()
Returns the value true if the argument is a letter, and false
otherwise.
isLetterOrDigit()
Returns the value true if the argument is a letter or a digit, and
false otherwise.
isWhitespace()
Returns the value true if the argument is whitespace, which is any
one of the characters:
space (' '),
tab (' \t '),
newline (' \n '),
carriage return (' \r '),
form feed (' \f ')
The method returns false otherwise.
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