Code Tracing
Given list = ["A", "B", "C"].
After executing the following code:
list.add(list.remove(0));
What does the list look like?
["B", "C", "A"]
Given list = [1, 2, 2, 3].
What does the list look like after this loop executes?
for (int i = 0; i < list.size(); i++) {
if (list.get(i) == 2)
list.remove(i);
}
[1, 2, 3]
What exception occurs if you call list.set(list.size(), "Value")?
IndexOutOfBounds
Why does for (int i = 0; i <= list.size(); i++) crash?
IndexOutOfBoundsException
ArrayList<Integer> nums = [1, 2, 3].
What is in the list after nums.remove(1)?
[1, 3]
Given list = [1, 2, 3, 4].
Trace the result of this loop:
for (int k = 0; k < list.size(); k++) {
list.set(k, list.get(k) + k);
}
[1, 3, 5, 7]
To correctly remove ALL occurrences of a value using a standard for loop, what specific change must you make to the (aka the l?
Iterate backwards (i--) OR decrement i inside the if-statement (i--)
What is the boolean return value of list.add(*object name and value*) for an ArrayList?
true
list = [1, 2, 3, 4].
int count = 0.
for (int x : list) {
if even, add x to count;
if odd, subtract x from count.
}
What is the value of count after the code above executes?
2
How do you remove the VALUE 1 from ArrayList<Integer> nums?
nums.remove(Integer.valueOf(1)) OR you can cast to an object
Given an empty list letters.
What does the list look like after the following lines of code are executed?
letters.add("A");
letters.add(0, "B");
letters.set(1, "C");
letters.add(1, "D");
["B", "D", "C"]
Given list = [1, 2, 2, 3].
What remains after this loop is executed?
for (int i = 0; i < list.size(); i++) {
if (list.get(i) == 2)
list.remove(i);
}
[1, 2, 3]
True or False: list.contains("apple") returns true if the list contains "Apple"
False!! Java is case-sensitive
What happens if you add to an ArrayList inside a loop that iterates up to list.size()?
Infinite Loop. The list size will keep increasing, meaning that whichever index you are at (let's say i for example) will always be less than list.size(), so the loop will continue to run forever.
List a = new ArrayList();
a.add(5);
List b = a;
b.add(6);
b.add(7);
What is a.size()?
3.
Remember, objects are handled by reference in Java. "List b = a;" means that the newly created variable b points to the same ArrayList instance in memory as a.
Trace the output:
ArrayList<Integer> nums = new ArrayList<>(); nums.add(3);
nums.add(4);
nums.add(5);
nums.add(1, nums.get(2) + nums.get(0));
[3, 8, 4, 5]
Given list = [10, 20, 30].
What is the output of the following line of code?
System.out.println(list.remove(1) + list.get(1));
50
If list is empty, what does
list.isEmpty() == (list.size() == 0)
evaluate to?
true
Why is the following code invalid for an ArrayList<Blue>? (Blue is a random class that you created)
if (list.get(i) > list.get(i+1))
You cannot use > and < directly to compare elements that are Objects
True/False: ArrayList<int> list = new ArrayList<int>(); compiles.
FALSE! You must type it as <Integer>
What is printed by this code?
List<String> list = new ArrayList<>(); list.add("Cat");
System.out.println(list.set(0, "Dog"));
Cat
Write the single line of code to remove the LAST element of any ArrayList named list.
list.remove(list.size() - 1);
If the goal is to add at the end of the list, the code
list.add(5, "Hello");
is ONLY valid if the list size is initially what number?
5
What is this code effectively doing?
for (int i = 0; i < list.size() / 2; i++)
swap(i, list.size() - 1 - i); // swaps the element at index i with the element at index (size -1 - i)
Reversing the list
Does the following code return true if both are distinct String objects with value "Hello"? Explain why or why not.
list.get(0) == list.get(1)
No, you should use .equals() with Strings