#041 Characters

Most of the time, if you are using a single character value, you will use the primitive char type. For example:

char ch = 'a'; 
char uniChar = 'u039A'; // Unicode for uppercase Greek omega character
char[] charArray ={ 'a', 'b', 'c', 'd', 'e' }; // an array of chars

There are times, however, when you need to use a char as an object—for example, as a method argument where an object is expected. The Java programming language provides a wrapper class that “wraps” thechar in a Character object for this purpose. An object of type Character contains a single field, whose type is char. This Character class also offers a number of useful class (i.e., static) methods for manipulating characters.

You can create a Character object with the Character constructor:

Character ch = new Character('a');

The Java compiler will also create a Character object for you under some circumstances. For example, if you pass a primitive char into a method that expects an object, the compiler automatically converts the charto a Character for you. This feature is called autoboxing—or unboxing, if the conversion goes the other way.

Here is an example of boxing,

Character ch = 'a'; // the primitive char 'a' is boxed into the Character object ch

and here is an example of both boxing and unboxing,

Character test(Character c) {...} // method parameter and return type = Character object

char c = test('x'); // primitive 'x' is boxed for method test, return is unboxed to char 'c'

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Note: The Character class is immutable, so that once it is created, a Character object cannot be changed.

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The following table lists some of the most useful methods in the Character class, but is not exhaustive. For a complete listing of all methods in this class (there are more than 50), refer to the java.lang.CharacterAPI specification.

 

Useful Methods in the Character Class

Method	Description
boolean isLetter(char ch) boolean isDigit(char ch)	Determines whether the specified char value is a letter or a digit, respectively.
boolean isWhiteSpace(char ch)	Determines whether the specified char value is white space.
boolean isUpperCase(char ch) boolean isLowerCase(char ch)	Determines whether the specified char value is uppercase or lowercase, respectively.
char toUpperCase(char ch) char toLowerCase(char ch)	Returns the uppercase or lowercase form of the specified char value.
toString(char ch)	Returns a String object representing the specified character value—that is, a one-character string.

Escape Sequences

A character preceded by a backslash () is an escape sequence and has special meaning to the compiler. The newline character (n) has been used frequently in this tutorial in System.out.println() statements to advance to the next line after the string is printed. The following table shows the Java escape sequences:

 

Escape Sequences

Escape Sequence	Description
t	Insert a tab in the text at this point.
b	Insert a backspace in the text at this point.
n	Insert a newline in the text at this point.
r	Insert a carriage return in the text at this point.
f	Insert a formfeed in the text at this point.
'	Insert a single quote character in the text at this point.
"	Insert a double quote character in the text at this point.
\	Insert a backslash character in the text at this point.

When an escape sequence is encountered in a print statement, the compiler interprets it accordingly. For example, if you want to put quotes within quotes you must use the escape sequence, “, on the interior quotes. To print the sentence

She said "Hello!" to me.

you would write

System.out.println("She said "Hello!" to me.");