How do HashMap.values() and HashMap.keySet() Retrieve Values and Keys in Java?

How do HashMap.values() and HashMap.keySet() retrieve values and keys in Java?

HashMap<String, Integer> map = new HashMap<>();
map.put("One", 1);
map.put("Two", 2);

// Retrieving values
Collection<Integer> values = map.values();
System.out.println(values);

// Retrieving keys
Set<String> keys = map.keySet();
System.out.println(keys);

In Java, the HashMap class is part of the java.util package and is used to store key-value pairs. The methods HashMap.values() and HashMap.keySet() allow you to retrieve all values and keys from a HashMap, respectively, facilitating easy manipulation and access to the data stored in the map.

// HashMap Example:
HashMap<String, Integer> map = new HashMap<>();
map.put("One", 1);
map.put("Two", 2);

Collection<Integer> values = map.values(); // returns [1, 2]
Set<String> keys = map.keySet(); // returns [One, Two]

Causes

• Understanding the purpose and functionality of HashMap in Java.
• Recognizing the difference between values and keys in HashMap.

Solutions

• Use HashMap.values() to get a Collection of values from the HashMap.
• Use HashMap.keySet() to get a Set of keys from the HashMap.
• Remember to import java.util.HashMap for successful implementation.

Mistake: Assuming the order of retrieval is guaranteed.

Solution: HashMap does not guarantee the order of keys or values. Use LinkedHashMap if order is important.

Mistake: Attempting to modify the key set or values collection directly.

Solution: To modify values or keys, you should update the HashMap directly instead of modifying the returned collections.