Creating a Generic HashMap Array

Question

For a homework assignment which is stated as:

In this homework, you will implement a key-value hash map with a external chaining collision policy. A hash map maps keys to values and allows O(1) average case lookup of a value when the key is known. This hash map must be backed by an array of initial size 11, and must have a size of 2n + 1 when the table exceeds (greater than, not greater than or equal to) a load factor of 0.67. The array must be resized before the new key (regardless of whether or not it’s a duplicate) is actually added into the array. The load factor and initial size values are provided as constants in the interface and should be used within your code.

We're given a MapEntry class already written, and a HashMap class to write up. How would I intialize this array? private MapEntry<K, V>[] table = new MapEntry<>[STARTING_SIZE]; doesn't work because of the generics situation.

@TimCastelijns A HashMap backed by an array, we can't use the Java Object — Joseph hooper
– Joseph hooper, Commented Sep 27, 2015 at 16:20
@laune you will implement a key-value hash map with a external chaining collision policy. This hash map must be backed by an array of initial size 11, and must have a size of 2n + 1 when the table exceeds (greater than, not greater than or equal to) a load factor of 0.67. The array must be resized before the new key (regardless of whether or not it’s a duplicate) is actually added into the array. The load factor and initial size values are provided as constants in the interface and should be used within your code. — Joseph hooper
– Joseph hooper, Commented Sep 27, 2015 at 16:22

laune · Accepted Answer · 2015-09-27 16:27:19Z

1

You omit the generic parameters in the array constructor:

Map.Entry<String,Integer>[] entries = new Map.Entry[11];

You can use an annotation @SuppressWarnings("unchecked") if the warning bothers you.

answered Sep 27, 2015 at 16:27

laune

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2 Comments

Joseph hooper Over a year ago

Okay so even though it gives an Unchecked assignment warning it'll still be good?

laune Over a year ago

@newacct Oops. Instant blackout. Thanks.

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