type can be converted properly into a string. valueOf( ) is also overloaded for type Object,
so an object of any class type you create can also be used as an argument. (Recall that Object
is a superclass for all classes.) Here are a few of its forms:
static String valueOf(double num)
static String valueOf(long num)
static String valueOf(Object ob)
static String valueOf(char chars[ ])
As we discussed earlier, valueOf( ) is called when a string representation of some other
type of data is needed--for example, during concatenation operations. You can call this method
directly with any data type and get a reasonable String representation. All of the simple types
are converted to their common String representation. Any object that you pass to valueOf( )
will return the result of a call to the object's toString( ) method. In fact, you could just call
toString( ) directly and get the same result.
For most arrays, valueOf( ) returns a rather cryptic string, which indicates that it is an
array of some type. For arrays of char, however, a String object is created that contains the
characters in the char array. There is a special version of valueOf( ) that allows you to specify
a subset of a char array. It has this general form:
static String valueOf(char chars[ ], int startIndex, int numChars)
Here, chars is the array that holds the characters, startIndex is the index into the array of
characters at which the desired substring begins, and numChars specifies the length of the
Changing the Case of Characters Within a String
The method toLowerCase( ) converts all the characters in a string from uppercase to
lowercase. The toUpperCase( ) method converts all the characters in a string from lowercase
to uppercase. Nonalphabetical characters, such as digits, are unaffected. Here are the general
forms of these methods:
String toLowerCase( )
String toUpperCase( )
Both methods return a String object that contains the uppercase or lowercase equivalent
of the invoking String.
Here is an example that uses toLowerCase( ) and toUpperCase( ):
// Demonstrate toUpperCase() and toLowerCase().
class ChangeCase {
public static void main(String args[])
String s = "This is a test.";
System.out.println("Original: " + s);
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