Principle of Indecent Exposure

Overview

Overview

Overview

I have previously discussed about different dimensions in Array Reification. Today, I am going to discuss about another important phenomena in Array Reification

Problem Domain

Let’s consider, we have a requirement to store several lists of results in an array container. We can write our program the following way.

public final class IndecentExposure {

	public static List<Integer>[] studentMarksLists() {
		final List<Integer>[] studentMarksLists = (List<Integer>[]) new List[2];

		final List<Integer> samMarks = Lists.newArrayList(40, 30, 48, 22, 98);
		final List<Integer> deanMarks = Lists.newArrayList(73, 98, 22, 73, 45);

		studentMarksLists[0] = samMarks;
		studentMarksLists[1] = deanMarks;

		return studentMarksLists;
	}

}

If you execute the program, you would encounter the famous Unchecked Cast warning message.

Now let’s try to retrieve Sam’s marks or Dean’s Marks.

public final class IndecentExposure {

	public static void main(final String[] args) {
		final List<Integer>[] studentMarksLists = IndecentExposure.studentMarksLists();
		final List<? extends Number>[] marksLists = studentMarksLists;
		marksLists[0] = Lists.newArrayList(20.23, 40.44, 50.44);
		final int num = studentMarksLists[0].get(0);
		System.out.println(num);
	}

	public static List<Integer>[] studentMarksLists() {
		final List<Integer>[] studentMarksLists = (List<Integer>[]) new List[2];

		final List<Integer> samMarks = Lists.newArrayList(40, 30, 48, 22, 98);
		final List<Integer> deanMarks = Lists.newArrayList(73, 98, 22, 73, 45);

		studentMarksLists[0] = samMarks;
		studentMarksLists[1] = deanMarks;

		return studentMarksLists;
	}

}

We have previously seen that generic array creation is not possible and that’s the reason we needed to use the raw type List to create the container and then we casted it to the required type.

Now, if we try to retrieve the value from the container, we would encounter Class cast exception as the aforementioned code replaces the first element of the array with a list of doubles.

You can see that here we have an array whose component type is List<Integer>. As the component type is not reifiable, the array accepted a List<? extends Number>. For which, the first element of the array got replaced by a list of doubles at runtime.