An array, which stores a
fixed-size sequential collection of elements of the same type. Think of an
array as a collection of variables of the same type.
Instead of declaring
individual variables, such as number0, number1, ..., and number99, you declare
one array variable such as numbers and use numbers[0], numbers[1], and ...,
numbers[99] to represent individual variables.
Declaring
Array Variables:
dataType[] arrayRefVar; // preferred way.
or
dataType arrayRefVar[]; // works but not preferred way.
Example:
double[] myList; // preferred way.
or
double myList[]; // works but not preferred way.
Creating
Arrays:
arrayRefVar = new dataType[arraySize];
·
It creates an array using new dataType[arraySize];
·
It assigns the reference of the newly created array to the
variable arrayRefVar.
Declaring an array variable,
creating an array, and assigning the reference of the array to the variable can
be combined in one statement, as shown below:
dataType[] arrayRefVar = new dataType[arraySize];
Alternatively you can create
arrays as follows:
dataType[] arrayRefVar = {value0, value1, ..., valuek};
Example:
Following statement declares
an array variable, myList, creates an array of 10 elements of double type and
assigns its reference to myList:
double[] myList = new double[10];
Following picture represents
array myList. Here, myList holds ten double values and the indices are from 0
to 9.
Processing
Arrays:
When processing array
elements, we often use either for loop or foreach loop because all of the
elements in an array are of the same type and the size of the array is known.
The
foreach Loops:
JDK 1.5 introduced a new for
loop known as foreach loop or enhanced for loop, which enables you to traverse
the complete array sequentially without using an index variable.
Passing
Arrays to Methods:
Just as you can pass
primitive type values to methods, you can also pass arrays to methods. For
example, the following method displays the elements in an int array:
public static void printArray(int[] array) {
for (int i = 0; i < array.length; i++) {
System.out.print(array[i] + " ");
}
}
You can invoke it by passing
an array. For example, the following statement invokes the printArray method to
display 3, 1, 2, 6, 4, and 2:
printArray(new int[]{3, 1, 2, 6, 4, 2});
Returning
an Array from a Method:
A method may also return an
array. For example, the method shown below returns an array that is the
reversal of another array:
public static int[] reverse(int[] list) {
int[] result = new int[list.length];
for (int i = 0, j = result.length - 1; i < list.length; i++, j--) {
result[j] = list[i];
}
return result;
}
