A Collection of Useful Classes - Beginning Java 2 SDK - page 546

boolean byte char float double

short int long Object

The version of fill() accepting an array argument of type Object[] will obviously process an array
of any class type.

Here's how you could fill an array of integers with a particular value:

long[] values = new long[1000];
java.util.Arrays.fill(values, 888L); // Every element as 888

It's a relatively common requirement to fill an array of type char[] with spaces. Here's how you might
use the fill() method in a method to put a value in a fixed width field:

// Return a value right justified in a field
public static String fixedWidth(double value, int width) {
String valStr = String.valueOf(value);
assert width> valStr.length();

char[] spaces = new char[width-valStr.length()];
java.util.Arrays.fill(spaces, ' '); // Fill array with blanks

return new StringBuffer().append(spaces).append(valStr).toString();
}

This converts the value passed as the first argument to a string and checks that the field width specified
is greater than the length of this string. The assertion ensures that we don't attempt to create an array
with a negative number of elements. We then create an array of type char[] that will provide the
spaces to the left of the value string. We fill this using the fill() method from the Arrays class in the
java.util package. We then assemble the field as a StringBuffer object by appending the array
followed by the value string and convert the result to type String before returning it. Clearly you
could easily create an overloaded version of this method to output values of any basic type in a fixed
width field. You could even embellish it with an option for left or right justification in the field.

There is a further form of fill() method that accepts four arguments. This is of the form:

fill( type [] array, int fromIndex, int toIndex, type value)

This will fill part of array with value , starting at array[fromIndex] up to and including
array[toIndex-1] . There are versions of this method for the same range of types at the previous set
of fill() methods. This variety of fill() will throw an exception of type
IllegalArgumentException if fromIndex is greater than toIndex . It will also throw an
exception of type ArrayIndexOutOfBoundsException if fromIndex is negative or toIndex is
greater than array.length .

We could have taken a different approach to the fixedWidth() method and used this version of
fill() in the process: