ArrayList Warm-Up: What’s in the List?

ArrayList Warm-Up: What’s in the List?

Reminder: What the Methods Return

Method	What it does	What it returns
add(E obj)	Adds obj to the end of the list	boolean (always true)
add(int index, E obj)	Inserts obj at index, shifting later elements right	nothing (void)
get(int index)	Looks at the element at index; the list is unchanged	the element at index
set(int index, E obj)	Replaces the element at index with obj	the old element that was at index
remove(int index)	Removes the element at index, shifting later elements left	the element that was removed
size()	Counts the elements; the list is unchanged	the number of elements

For each problem, write down the contents of the ArrayList after the code runs, in the same format System.out.println would print it (for example, [3, 5, 7]). Some problems also ask for the value of a variable.

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Part 1: No Loops

Problem 1

ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(4);
nums.add(8);
nums.add(15);
nums.set(1, nums.get(0) + nums.get(2));
nums.add(1, nums.get(2) - 5);
nums.set(3, nums.get(1) * 2);
nums.add(nums.get(0));

What is in nums?

Problem 2

ArrayList<String> words = new ArrayList<String>();
words.add("red");
words.add("green");
words.add("blue");
String old = words.set(0, "yellow");
words.add(old);
words.set(3, words.set(2, "purple"));
words.add(1, words.get(3));

What is in words? What is the value of old?

Problem 3

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(5);
list.add(10);
list.add(15);
list.add(20);
list.add(25);
int a = list.remove(2);
list.add(1, a);
list.set(0, list.remove(3));
list.add(list.get(1) - list.get(2));

What is in list? What is the value of a?

Problem 4

ArrayList<String> items = new ArrayList<String>();
items.add("A");
items.add("B");
items.add("C");
items.add("D");
items.add("E");
String x = items.remove(1);
String y = items.set(2, x);
items.add(1, y);
items.set(0, items.remove(items.size() - 1));

What is in items? What are the values of x and y?

Problem 5

ArrayList<Integer> data = new ArrayList<Integer>();
data.add(2);
data.add(4);
data.add(6);
data.add(8);
data.add(10);
data.add(12);
data.set(1, data.remove(4));
data.add(2, data.get(0) + data.remove(3));
data.remove(data.get(0) - 1);
data.set(data.size() - 1, data.get(1) + data.get(2));

What is in data?

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Part 2: With Loops

Problem 6

ArrayList<Integer> multiples = new ArrayList<Integer>();
for (int i = 1; i <= 10; i++)
{
    if (i % 3 == 0)
    {
        multiples.add(i);
    }
}

What is in multiples?

Problems 7-10

Each of the following problems starts with a fresh copy of this list:

ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(2);
nums.add(4);
nums.add(6);
nums.add(8);
nums.add(10);
nums.add(12);

Problem 7

for (int i = 0; i < 3; i++)
{
    nums.add(0, i);
}

What is in nums?

Problem 8

for (int i = 0; i < 3; i++)
{
    int first = nums.remove(0);
    nums.add(first + 1);
}

What is in nums?

Problem 9

for (int i = nums.size() - 1; i >= 0; i--)
{
    if (nums.get(i) > 5)
    {
        nums.remove(i);
    }
}

What is in nums?

Problem 10

for (int i = 0; i < nums.size(); i++)
{
    if (nums.get(i) > 5)
    {
        nums.remove(i);
    }
}

What is in nums? Compare your answer to Problem 9. Why do the two differ?