CodeHS 5.8 HashMaps

What is a HashMap?

• a bunch of key-value pairs

• a type of ArrayList

• a type of 2D array

• a type of 3D array

How many values can each key in a HashMap be associated with?

• one

• depends how you initialize the HashMap

• unlimited

• trick question--keys aren't associated with values in a HashMap

Which of these lines of code creates a HashMap called foo that has an int for keys and a String for values?

• 
• 
• 
• 

Which line of code will add a second phone number "312-423-1234" to Charles Babbage?

• phonebook.put("Charles Babbage", "312-423-1234");

• phonebook.put("Charles Babbage", "312-423-1234")

• phonebook.put("312-423-1234", "Charles Babbage");

• trick question--you can't add a second value to a key

What will be printed to the screen when the following code is executed:

System.out.println(phonebook.get("Grace Hopper"));

• "650-352-7500"

• 650-352-7500

• [phone]

• "[phone]"

• Grace Hopper

What do you use to access every member of a HashMap?

• a for loop

• a for-each loop

• an array

• an ArrayList

What do you use to find out how many key-value pairs are in the HashMap named bar?

• bar.size()

• bar.length

• bar.size

• bar.length()

What method is used to remove a key-value pair from a HashMap?

• remove(key)

• delete(key)

• erase(key)

• clear(key)

What happens if you try to get a value in a HashMap using a key that does not exist?

• Returns null

• Throws an exception

• Returns default value

• Program crashes

Can a HashMap store multiple null values?

• Yes, multiple null values are allowed

• No, only one null value is allowed

• No, null values are not allowed

• Yes, but only if keys are not null