Sharing of efficient use tips for HashMap and HashSet in Java

Java HashMap

HashMapis a hash table that stores key-value pairs. Keys are used to find values, just like indexes in arrays.HashMapThe advantage is that it can use any type as a key and the lookup is very fast.

Create a HashMap

// Import HashMap classimport ;

public class Main {
    public static void main(String[] args) {
        // Create a HashMap object named capitalCities that will store the String key and String value        HashMap<String, String> capitalCities = new HashMap<>();
    }
}

Add a project

// Add keys and values ​​(country, city)("England", "London");
("Germany", "Berlin");
("Norway", "Oslo");
("USA", "Washington DC");

Visit the project

// Get the capital of EnglandString capitalOfEngland = ("England");

Delete the project

// Delete the capital of England("England");

HashMap size

// Get the number of items in HashMapint size = ();

Looping through HashMap

// traverse HashMap and print keys and valuesfor (String key : ()) {
    String value = (key);
    ("Key: " + key + ", Value: " + value);
}

Use other types

HashMapAny type of keys and values ​​can be stored. For example, you can storeIntegerKeys andStringvalue:

// Create a HashMap object named people that will store the Integer key and String valueHashMap<Integer, String> people = new HashMap<>();

// Add key and value (ID, name)(1, "John Doe");
(2, "Jane Doe");

// Get the name with ID 1String name = (1);

HashMapIt is a powerful data structure that can be used to store various types of data. It has fast lookup speed and flexible key-value pair storage mechanisms, making it ideal for many applications.

Advantages of HashMap:

• Quickly find speed
• Can store any type of keys and values
• Flexible key-value pair storage mechanism

Disadvantages of HashMap:

• Not thread-safe
• There may be a hash collision

suggestion:

• If you need to quickly find data, please useHashMap。
• If you need a thread-safe data structure, please useConcurrentHashMap。
• If you need to avoid hash collisions, please useLinkedHashMap。

Java HashSet

HashSetis an unordered collection where each element is unique. It is implemented based on a hash table, so the lookup is fast.

Create a HashSet

// Import HashSet classimport ;

public class Main {
    public static void main(String[] args) {
        // Create a HashSet object named cars that will store the string        HashSet<String> cars = new HashSet<>();
    }
}

Add a project

// Add a project("Volvo");
("BMW");
("Ford");
("BMW"); // Will not be added repeatedly("Mazda");

// View HashSet(cars);

Check if the item exists

// Check whether the item existsboolean isPresent = ("Mazda");

// Output result("Is Mazda in HashSet?" + isPresent);

Delete the project

// Delete the project("Volvo");

// View HashSet(cars);

HashSet Size

// Get the HashSet sizeint size = ();

// Output result("HashSet Size:" + size);

Looping through HashSet

// Loop through HashSetfor (String car : cars) {
    (car);
}

Use other types

HashSetElements of any type can be stored. For example, you can storeIntegerelement:

// Create a HashSet object named numbers that will store integersHashSet<Integer> numbers = new HashSet<>();

// Add elements(1);
(2);
(3);

// Loop through HashSetfor (int number : numbers) {
    (number);
}

HashSetIt is a very useful data structure that can be used to store various types of data. It has the characteristics of fast search speed and disorder, making it ideal for many applications.

Advantages of HashSet:

• Quickly find speed
• Unorder, allowing for faster addition and removal of elements
• Allows storage of any type of elements

Disadvantages of HashSet:

• The insertion order of elements is not preserved
• There may be a hash collision

suggestion:

• If you need to quickly find data and do not need to preserve the insertion order of elements, useHashSet。
• If you need to preserve the insertion order of elements, useLinkedHashSet。
• If you need to avoid hash collisions, please useTreeMap。

This is the end of this article about the efficient use skills of HashMap and HashSet in Java. For more related Java HashMap HashSet content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!