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Subgoals

Section 13.10 ArrayLists-WE4-P1

Subgoals for Evaluating ArrayLists.

  1. 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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  2. Determine access or change of element, or action on entire ArrayList object, and update elements as needed (remembering assignment subgoals)
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  3. 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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  4. 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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  5. 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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Subsection 13.10.1

Exercises Exercises

1.
Q16: Given the following code, what is the value in sum after execution?
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ArrayList<Integer> alpha = new ArrayList<>();
alpha.add(2); alpha.add(4); alpha.add(6); alpha.add(8); 
alpha.add(10); alpha.add(12); alpha.add(14);
int sum = 0;
for (int k = 0; k < alpha.size(); k+=2)
    sum = sum + alpha.get(k);
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2.
Q17: Given the following code, what is the value in sum after execution?
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ArrayList<Integer> beta = new ArrayList<>();
for (int i = 0; i < 5; i++) {
    beta.add(0);
}
int sum = 0;
for (int k = 0; k < beta.size(); k++)
    beta.set(k, 2 * k + 1);
int x = 3;
for (int k = 1; k < beta.size(); k++)
    sum += beta.get(k);
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