Assessment: ArrayLists 1

Section 13.8 Assessment: ArrayLists 1

Subgoals for Evaluating ArrayLists.

Declaring and initialization of an ArrayList
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1. Set up a one-dimensional dynamic list (initially empty or with a specified initial capacity)
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2. Upon instantiation, an ArrayList contains zero elements initially, but elements can be added dynamically using add(). Elements not yet added do not exist until explicitly inserted.
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Determine access or change of element, or action on entire ArrayList object, and update elements as needed (remembering assignment subgoals)
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Accessing an ArrayList element
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1. Evaluate expression within get(index) which will be the index for the element to be accessed
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2. arrayListName.get(index) returns the value stored at that index
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3. index must be between 0 and arrayListName.size() - 1, inclusive; otherwise IndexOutOfBoundsException occurs
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Changing value of an ArrayList element
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1. Evaluate expression within set(index, value) which will be the index for the element to be replaced
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2. arrayListName.set(index, value) replaces the element at index with the specified value
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3. (remember the assignment subgoals for verifying data types and evaluating expressions)
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4. (remember rules for index values)
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Whole ArrayList actions
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1. Passing as argument - a copy of the reference to the instantiated ArrayList is passed to the method. This means that any changes made to the elements inside the method persist outside the method. The exception is if the argument is assigned to reference a different ArrayList inside the method.
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2. Assignment - changes the reference to point to the ArrayList on the right-hand side of the assignment operator.
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Exercises Exercises

1.

Q1: Assuming that the following declaration has been made, which of the following code segments correctly interchanges the value of arr.get(0) and arr.get(5)?

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ArrayList<Integer> arr = new ArrayList<>(Arrays.asList(5, 12, -22, 6, 11, 0, 26, 42, 99, 75));

arr.set(0, 5); arr.set(5, 0);
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arr.set(0, arr.get(5)); arr.set(5, arr.get(0));
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int k = arr.get(5); arr.set(0, arr.get(5)); arr.set(5, k);
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int k = arr.get(0); arr.set(0, arr.get(5)); arr.set(5, k);
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int k = arr.get(5); arr.set(5, arr.get(0)); arr.set(0, arr.get(5));
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2.

Q2: Consider the following code that is intended to print true if all the elements in arr are even numbers; otherwise it should print false. You may assume that arr has been declared and contains valid integer values.

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ArrayList<Integer> arr = new ArrayList<>(Arrays.asList(2, 4, 6, 8, 10));
boolean isEven = /* expression */;
for (int k = 0; k < arr.size(); k++) {
   /* loop body */
}
if (isEven)
    System.out.println("TRUE");
else
    System.out.println("FALSE");

Which of the following replacements for /* expression */ and /* loop body */ should be used so that the code works as intended?

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/* expression */: false /* loop body */: if ((arr.get(k) % 2) == 0) isEven = true;
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/* expression */: false /* loop body */: if ((arr.get(k) % 2) != 0) isEven = false; else isEven = true;
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/* expression */: true /* loop body */: if ((arr.get(k) % 2) != 0) isEven = false;
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/* expression */: true /* loop body */: if ((arr.get(k) % 2) != 0) isEven = false; else isEven = true;
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/* expression */: true /* loop body */: if ((arr.get(k) % 2) == 0) isEven = false; else isEven = true;
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3.

Q3: Considering the following code, what are the values in numbers after execution?

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ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(17, 34, 21, 42, 15, 69, 48, 25, 39));
int x = 3;
for (int k = 1; k < 9; k = k + x)
   numbers.set(k, numbers.get(k - 1) + x);

<17, 20, 21, 42, 45, 69, 48, 51, 39>
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<17, 20, 23, 26, 29, 32, 35, 38, 41>
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<17, 37, 21, 42, 18, 69, 48, 28, 39>
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<20, 23, 21, 42, 45, 69, 51, 54, 39>
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<20, 34, 21, 45, 15, 69, 51, 25, 39>
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