# Unit 4B - Toggle Code Practice 4b ArrayList (4.7-4.10)

Each coding exercise has its own folder. Open its `.java` file and press **Run** to try it. **Run Tests** checks every graded exercise in this lesson at once.

For each of the coding problems below, write your own solution.

## Exercise 1

The following program should create an ArrayList called `conversation`, add in some elements(`"hello"`, `"goodbye"`, `"how are you"`, and `"see you later"`), and print out the elements with `", "` after each. Fill in the code so that it adds the elements to `conversation`. The rest of the program is finished for you.

> Open the `01-u4b-toggle1` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 2

Fix the two errors in the `printBackwards` method so that it will correctly iterate through the parameter `myList` backwards and print each element.

> Open the `02-u4b-toggle2` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 3

Write code to define the `removeZeros` method. This method should take in an ArrayList of integers `listOfNums` and delete all of the zeros. For example, `{3, 0, 5, 0}` would change into `{3, 5}`.

> Open the `03-u4b-toggle3` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 4

Write code for the `findSmallest` method. This code segment should take in an ArrayList `nums` and return the smallest element present. For example, `findSmallest` called on `{5, 3, 1, 6}` should return `1`.

> Open the `04-u4b-toggle4` folder and edit `ListTest.java`. This one is not graded, so check it yourself.

## Exercise 5

Write code to flesh out the `removeOdd` method. This method should take in a parameter `nums` and delete every odd number from it. For example, `{5, 3, 2, 1, 4}` should become `{2, 4}`.

> Open the `05-u4b-toggle5` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 6

Fill out the `average` method. It should take in an ArrayList `nums` and calculate the arithmetic mean (the sum divided by the length). For example, `average` called on `{5, 9, 6}` should return `6.66666666667` as that is `(5 + 9 + 6) / 3`.

> Open the `06-u4b-toggle6` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 7

Create the `moveLargest` method. This should find the largest value in an ArrayList of Integers (the parameter) and move it to the back of the list.

> Open the `07-u4b-toggle7` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 8

Write code to finish the `removeShort` method. It should take an ArrayList `words` and remove all elements that are three characters long or shorter. For example, `{"Dog", "Monkey", "Lion", "Cat"}` would become `{"Monkey", "Lion"}`.

> Open the `08-u4b-toggle8` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 9

Write the method `doubleList`. This should take in an ArrayList `words` and insert a copy of each element such that `{"cat", "ribbon", "house"}` would become `{"cat", "cat", "ribbon", "ribbon", "house", "house"}`.

> Open the `09-u4b-toggle9` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).

## Exercise 10

Write the method `removeElement`. This should take in an ArrayList `nums` and an integer `toRemove` and remove every instance of that integer from `nums`. E.g., if nums was `{3, 6, 5, 3, 4}`, it should become `{6, 5, 4}` after calling `removeElement(nums, 3)`.

> Open the `10-u4b-toggle10` folder and edit `ListTest.java`. Press **Run** to try it; **Run Tests** checks it (1 test).