Anonymous Arrays
As shown earlier in this section, the following declaration statement can be used to construct arrays using an array creation expression:
element_type
1
[]
array_name
= new
element_type
2
[
array_size
]; // (1)
int[] intArray = new int[5];
The size of the array is specified in the array creation expression, which creates the array and initializes the array elements to their default values. By comparison, the following declaration statement both creates the array and initializes the array elements to specific values given in the array initializer:
element_type
[]
array_name
= {
array_initialize_list
}; // (2)
int[] intArray = {3, 5, 2, 8, 6};
However, the array initializer is not an expression. Java has another array creation expression, called an anonymous array, which allows the concept of the array creation expression from (1) to be combined with the array initializer from (2), so as to create and initialize an array:
new
element_type
[] {
array_initialize_list
}
new int[] {3, 5, 2, 8, 6}
This construct has enough information to create a nameless array of a specific type and specific length. Neither the name of the array nor the size of the array is specified. The construct returns the reference value of the newly created array, which can be assigned to references and passed as arguments in method calls. In particular, the following declaration statements are equivalent:
int[] intArray = {3, 5, 2, 8, 6}; // (1)
int[] intArray = new int[] {3, 5, 2, 8, 6}; // (2)
At (1), an array initializer is used to create and initialize the elements. At (2), an anonymous array expression is used. It is tempting to use the array initializer as an expression—for example, in an assignment statement, as a shortcut for assigning values to array elements in one go. However, this is not allowed; instead, an anonymous array expression should be used. The concept of the anonymous array combines the definition and the creation of the array into one operation.
int[] daysInMonth;
daysInMonth = {31, 28, 31, 30, 31, 30,
31, 31, 30, 31, 30, 31}; // Compile-time error
daysInMonth = new int[] {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; // OK
In Example 3.8, an anonymous array is constructed at (1), and passed as an actual parameter to the static method findMinimum() defined at (2). Note that no array name or array size is specified for the anonymous array.
Example 3.8 Using Anonymous Arrays
public class AnonArray {
public static void main(String[] args) {
System.out.println(“Minimum value: ” +
findMinimum(new int[] {3, 5, 2, 8, 6})); // (1)
}
public static int findMinimum(int[] dataSeq) { // (2)
// Assume the array has at least one element.
int min = dataSeq[0];
for (int index = 1; index < dataSeq.length; ++index)
if (dataSeq[index] < min)
min = dataSeq[index];
return min;
}
}
Output from the program: Minimum value: 2