hashmap + java-visual

Which programming language is used to implement the HashMap in the image?

• A: Java [Image shows the text "HashMap in Java" in the image.]
• B: C++
• C: Python
• D: Ruby

Answer explanation

The image shows a diagram of a HashMap in Java. The text in the image also confirms that the HashMap is implemented in Java. Therefore, the answer must be A: Java.

The image shows a diagram of a hash table. Which of the following statements is true about the keys in the diagram?

• All of the keys have the same hash code.
• All of the keys have different hash codes.
• Some of the keys have the same hash code, but different key content.
• None of the keys have the same hash code.

Answer explanation

The text in the image says that the keys "Key 1 to Key5" have the same hash code values, but different key content. This is confirmed by the diagram, which shows that all five keys are stored in the same bucket.

Which of the following classes in the Java Collections Framework implements the Map interface?

• HashMap
• ConcurrentSkipListMap
• EnumMap
• TreeMap

Answer explanation

The answer is HashMap. This is because HashMap is a class in the Java Collections Framework that implements the Map interface. The Map interface defines a map as a collection of key-value pairs. HashMap stores key-value pairs in a hash table, which allows for fast access to the values.

What is the default capacity of the nodes in the image?

• 8
• 16
• 32
• 64

Answer explanation

The answer is 16, which is shown in the image in the text box labeled "Default capacity". The text box also shows that the default capacity is equal to the value of the constant e.

Which of the following is NOT a bucket?

• 0
• 2
• 3
• 45

Answer explanation

The answer is 0, because it is not a bucket. Buckets are represented by the numbers 1, 2, and 3 in the image. The number 0 is simply a placeholder for the first bucket, which is empty.

What is the purpose of the listIterator variable in the Java code?

• To iterate through the list in both forward and backward directions.
• To create a new list iterator object.
• To get the next element in the list.
• To remove the current element in the list.

Answer explanation

The listIterator variable is a ListIterator object, which is a type of iterator that can be used to iterate through a list in both forward and backward directions. This is because the ListIterator interface has methods for both hasNext() and previous(), which allow the iterator to move forward and backward through the list.

How does a HashMap store key-value pairs?

• A. It uses a linked list to store each key-value pair.
• B. It uses an array to store each key-value pair.
• C. It uses a hash table to store each key-value pair.
• D. It uses a combination of a hash table and a linked list to store each key-value pair.

Answer explanation

The image shows that a HashMap stores key-value pairs in a hash table. However, if two keys have the same hash code, they will be stored in the same bucket in the hash table. To resolve this collision, the HashMap uses a linked list to store all of the key-value pairs that have the same hash code.

Which of the following classes is a concrete implementation of the Map interface?

• AbstractMap
• HashMap
• LinkedHashMap
• TreeMap

Answer explanation

The answer is HashMap because it is the only class in the image that is labeled as a concrete implementation of the Map interface. The other classes are all abstract classes or interfaces.

How are key objects mapped to bucket indexes in a hash table?

• A hash function is used to convert the key object into a unique integer value.
• The key object is compared to all of the other key objects in the hash table.
• The key object is stored in the bucket index that corresponds to its ASCII value.
• The key object is stored in the bucket index that corresponds to its hash code.

Answer explanation

A hash table is a data structure that uses a hash function to map key objects to bucket indexes. The hash function takes a key object as input and produces a unique integer value as output. This integer value is then used to index into the hash table, where the key object is stored.

Which of the following nodes is stored in bucket 3?

• A node with key "hello" and value "world"
• A node with key "goodbye" and value "bye"
• A node with key "world" and value "hello"
• A node with key "bye" and value "goodbye"

Answer explanation

The answer is (C) A node with key "world" and value "hello". This is because the key "world" has a hash value of 3, and the node with key "world" and value "hello" is stored in bucket 3. The other nodes in the image have different hash values, and they are stored in different buckets.