Question

(Using the Enhanced for Statement) Write an application that uses an enhanced for statement to sum the double values passed by the command-line arguments. [Hint: Use the static method parseDouble of class Double to convert a String to a double value.

Short answer

Initialize a sum variable, use an enhanced for loop to iterate over command-line arguments, convert each argument to double with 'Double.parseDouble' and sum them up, then print the result.

Step-by-step solution

Understand the Enhanced for Statement

The enhanced for statement, also known as the for-each loop, is used for iterating through elements of an array or a collection. It is written as 'for (Type var : array)' where 'Type' is the data type of the elements, 'var' is the variable that refers to the current element in the loop, and 'array' is the array or collection being iterated over.

Write the Main Method

Start by creating a main method that will take command-line arguments. The command-line arguments are passed as a String array to the main method. The syntax is 'public static void main(String[] args) { }'. Within this method, you will process the command-line arguments.

Parse String Arguments to Doubles

Inside the main method, initialize a variable to hold the sum of double values. Then, use an enhanced for statement to iterate over 'args', which contains the command-line arguments. For each iteration, use 'Double.parseDouble' to convert the current String argument to a double value and add it to the sum.

Sum the Double Values

As you parse each String argument to a double using 'Double.parseDouble', add this value to the sum variable that you initialized. Make sure to handle any potential 'NumberFormatException' that may occur if the argument cannot be parsed to a double.

Print the Result

After the for-each loop has processed all command-line arguments, print out the final sum.

Key concepts

Enhanced For Statement

The enhanced for statement, commonly referred to as the for-each loop, greatly simplifies iterating over arrays and collections in Java by automatically handling the indexing and bounds checking. In practice, you'll write something akin to 'for (double value : valuesArray)' where 'double' is the data type expected in the array, 'value' is the variable representing the current element, and 'valuesArray' is the array you're iterating over. Instead of manually controlling a loop counter and retrieving the array element at that index, the enhanced for loop provides direct access to each element, one at a time.

For our command-line argument summing exercise, this means we can directly process each argument provided without fussing about array indices. It simplifies the code and minimizes the risk of errors like an 'ArrayIndexOutOfBoundsException' due to incorrect index handling.

ParseDouble Method

When dealing with user input or in our case, command-line arguments in Java, values are often received as strings that need conversion to be used numerically. The 'parseDouble' method from the 'Double' class is our go-to solution for converting string representations of doubles into actual double values. The usage is straightforward: 'double numericValue = Double.parseDouble(stringValue);'.

However, it's critical to be aware of the format of the string being converted. The string should represent a valid double value; otherwise, you'll encounter a 'NumberFormatException'. Always implement error handling when using 'parseDouble' to ensure that your program can cope with unexpected or incorrect input gracefully.

NumberFormatException

When converting a string to a numeric type in Java, you may occasionally face a 'NumberFormatException'. This runtime exception is thrown to indicate that the application has attempted to convert a string to one of the numeric types, but the string does not have the appropriate format. It's common when dealing with external input - like user entries or, in our case, command-line arguments.

To handle this situation when summing our command-line double values, we could wrap our 'parseDouble' calls in a try-catch block. This way, if any of the command-line arguments aren't valid double values, our application can catch the 'NumberFormatException' and take appropriate action, such as ignoring the invalid argument and moving on to the next one, or providing a meaningful error message to the user.

Array Iteration

Array iteration is the process of systematically accessing each element within an array. While the enhanced for statement is one method of array iteration that is particularly useful for readability and convenience, there are other methods as well. The traditional for loop, with a counter variable tracking the index, is still relevant when you need more control over the iteration, such as being able to manipulate the index or handle multi-dimensional arrays. Regardless of the method used, iterating over arrays is a fundamental operation that enables us to perform tasks on a collection of elements, such as calculating a sum, as we have done with command-line arguments in this exercise.

An important part of array iteration is ensuring that we do not exceed the bounds of the array, which would cause an 'ArrayIndexOutOfBoundsException'. This is automatically managed in the enhanced for statement, but must be manually controlled in traditional for loops. For the exercise at hand, the enhanced for loop's simplicity is ideal for our need to process a linear set of arguments.