Data
Conversion Using valueOf( )
The valueOf( ) method converts data from its internal format into a
human-readable form. It is a static method that is overloaded within String for all of Java’s built-in types
so that each 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 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 substring.
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