A Collection of Useful Classes - Beginning Java - page 684

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 quite easy to initialize multidimensional arrays, too. To initialize a two-dimensional array, for ex-
ample, you treat it as an array of one-dimensional arrays. For example:
int[][] dataValues = new int[10][20];
for(int[] row : dataValues) {
Arrays.fill(row, 99);
}
The for loop sets every element on the dataValues array to 99. The loop iterates over the 10 arrays of
20 elements that make up the dataValues array. If you want to set the rows in the array to different values,
you could do it like this:
int initial = 0;
int[][] dataValues = new int[10][20];
for(int[] row : dataValues) {
Arrays.fill(row, ++initial);
}
This results in the first row of 20 elements being set to 1, the second row of 20 elements to 2, and so on
through to the last row of 20 elements that is set to 10.
The version of fill() that accepts an argument of type Object[] obviously processes an array of any
class type. You could fill an array of Person objects like this:
Person[] people = new Person[100];
java.util.Arrays.fill(people, new Person("John", "Doe"));
This inserts a reference to the object passed as the second argument to the fill() method in every ele-
ment of the people array. Note that there is only one Person object that all the array elements reference.
Another version of fill() accepts four arguments. This is of the form:
fill( type [] array, int fromIndex, int toIndex, type value)
This fills part of array with value, starting at array[fromIndex] up to and including ar-
ray[toIndex-1] . There are versions of this method for the same range of types as the previous set of
fill() methods. This variety of fill() throws an IllegalArgumentException if fromIndex is greater
than toIndex . It also throws an ArrayIndexOutOfBoundsException if fromIndex is negative or toIndex
is greater than array.length . Here's an example of using this form of the fill() method:
Person[] people = new Person[100];
java.util.Arrays.fill(people, 0, 50, new Person("Jane", "Doe"));
java.util.Arrays.fill(people, 50, 100, new Person("John", "Doe"));