Writing-ArrayLists-WE2-P1

Section 14.4 Writing-ArrayLists-WE2-P1

Subgoals for Evaluating ArrayLists.

Importing the ArrayList class
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1. Before using ArrayList, import it from the java.util package:
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  import java.util.ArrayList;
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Declaring an ArrayList variable
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1. Determine the type of objects to be stored (use wrapper classes for primitives, e.g., Integer instead of int)
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2. Determine the name of the ArrayList variable
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3. Use syntax: ArrayList<DataType> name;
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Instantiating an ArrayList object
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1. Use the new keyword with the constructor to create a new ArrayList object
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2. Assign to variable using: name = new ArrayList<>();
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3. Optionally, initialize with values using: new ArrayList<>(List.of(value1, value2, ...)); (Java 9+)
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Accessing an element in an ArrayList
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1. Determine the index of the element to be accessed
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2. Use: listName.get(index) to retrieve the element
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3. Ensure the index is within bounds: 0 to listName.size() - 1, otherwise an IndexOutOfBoundsException occurs
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Changing a value in an ArrayList
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1. Determine the index of the element to be changed
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2. Determine the new value or expression to assign
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3. Use: listName.set(index, newValue) to update the value
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Traversing an ArrayList
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1. Decide whether accessing all elements, updating, or accessing a subset
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2. If accessing only, use an enhanced for (for-each) loop:
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  1. for (DataType item : listName) - iterates from first to last, storing a copy of each element in item
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3. If updating or using indices, use a traditional for loop:
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  1. Initialize loop control variable to 0 (or listName.size() - 1 for reverse)
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  2. Set condition: i < listName.size() (or i >= 0 for reverse)
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  3. Increment or decrement loop control variable appropriately
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4. Use listName.get(i) to access or listName.set(i, newValue) to update
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Whole list actions
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1. Passing an ArrayList as an argument
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  1. Check if the method expects an ArrayList argument (check documentation or method signature)
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  2. Pass the ArrayList variable in the method call
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  3. Note: changes to the ArrayList in the method will persist (objects are passed by reference)
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2. Reassigning an ArrayList
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  1. Determine that the reference to the list should point to a new ArrayList
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  2. Left-hand side is the variable name of the original list
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  3. Right-hand side is the new ArrayList, e.g., new ArrayList<>()
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Subsection 14.4.1

Exercises Exercises

1.

Q4: What are the contents of alpha after this code has been executed?

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import java.util.ArrayList;

ArrayList<Integer> alpha = new ArrayList<>();
Collections.addAll(alpha, 10, 20, 30, 40, 50, 60, 70);

int start = alpha.get(alpha.size() - 1);
for (int i = 1; i < alpha.size(); i++) {
    alpha.set(i, alpha.get(i - 1));
}
alpha.set(0, start);

{20, 30, 40, 50, 60, 70, 10}
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{10, 20, 30, 40, 50, 60, 70}
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{10, 10, 20, 30, 40, 50, 60}
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{70, 10, 10, 10, 10, 10, 10}
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{10, 10, 10, 10, 10, 10, 10}
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2.

Q5: What are the contents of beta after this code has been executed?

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import java.util.ArrayList;

ArrayList<Integer> beta = new ArrayList<>();
Collections.addAll(beta, 10, 20, 30, 40, 50, 60, 70);

for (int i = 1; i < beta.size(); i++) {
    beta.set(i, beta.get(i - 1));
}

{20, 30, 40, 50, 60, 70, 10}
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{10, 20, 30, 40, 50, 60, 70}
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{10, 10, 20, 30, 40, 50, 60}
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{70, 10, 20, 30, 40, 50, 60}
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{10, 10, 10, 10, 10, 10, 10}
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3.

Q6: What happens when this code is executed on gamma?

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import java.util.ArrayList;

ArrayList<Integer> gamma = new ArrayList<>();
Collections.addAll(gamma, 10, 20, 30, 40, 50, 60, 70);

for (int i = 0; i < gamma.size(); i++) {
    gamma.set(i, gamma.get(i + 1));
}

{20, 30, 40, 50, 60, 70, 70}
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{20, 30, 40, 50, 60, 70, 10}
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{10, 20, 30, 40, 50, 60, 70}
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{10, 10, 20, 30, 40, 50, 60}
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IndexOutOfBounds Exception
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