Introduction to container technology in Java language

In the Java language, container technology is one of the very important concepts. It refers to a structure that can store and manage a group of objects. Container technology in Java involves multiple classes and interfaces, including common containers such as List, Set, and Map. These data structures provide convenient methods and tools that allow programmers to process data more efficiently. This article will introduce container technology in the Java language, including container types, common container classes, container operations, and container implementation methods.

1. Container Type

Containers in Java can be divided into two types: Collection and Map.

1. Collection

Collection is a collection of objects, which usually have the same type. Common Collection classes are:

• List: It is an ordered collection in which elements can be repeated. Null elements are allowed. Common implementation classes include ArrayList, LinkedList, etc.
• Set: It is a set that does not allow duplicate elements and can allow null elements. Common implementation classes include HashSet, LinkedHashSet, etc.
• Queue: It is a special List and Set, which only allows inserting elements at one end of the container and deleting elements at the other end, so it is a queue. Common implementation classes include LinkedList, PriorityQueue, etc.
• Stack: It is a LIFO (Last In First Out) structure that can insert and delete elements at one end of the container. Commonly used implementation classes include Stack.

2. Map

Map is a mapping set of keys and values, which allows us to find values ​​by key. The keys in the Map are unordered and cannot be repeated, but the values ​​can be repeated. Common implementation classes include HashMap, Hashtable, LinkedHashMap, etc.

2. Common container classes

1. ArrayList

ArrayList is a dynamic array, ordered, and it can automatically expand its capacity as needed. It inherits the AbstractList class and implements the List interface. Its underlying layer is an array, and elements can be accessed using subscripts. ArrayList allows null values ​​and it can be accessed randomly (O(1)). However, elements need to be moved during insertion and deletion operations, so performance is poor.

2. LinkedList

LinkedList is a linked list, ordered, and it can automatically expand its capacity as needed. It inherits the AbstractSequentialList class and implements the List, Deque, and Queue interfaces. LinkedList does not support random access, but has better performance during insertion and deletion operations. Synchronization is not supported and manual synchronization is required.

3. HashSet

HashSet is a hash table that does not allow duplicate elements to be stored. When storing an element, you first need to hash the element into a value of type int and then store the value in the array. If a hash collision occurs, a linked list is stored at the same location. HashSet implements the Set interface, which does not guarantee the order of elements.

4. LinkedHashSet

LinkedHashSet inherits HashSet, which maintains the order in which the elements of the collection are inserted, that is, it retains the order in which the elements are inserted.

5. HashMap

HashMap is a hash table that stores key-value pairs. When we insert an element, it first hashes the key of the element into an int type value, and then uses this value to determine where the key-value pair needs to be placed in the array. If a hash collision occurs, a linked list is stored at the same location. HashMap allows null keys and null values.

6. LinkedHashMap

LinkedHashMap inherits HashMap, which maintains a doubly linked list and maintains the order in which collection elements are inserted.

3. Container Operations

Commonly used operations on container instances are:

1. Add

Use the add() method to add elements to the end of the container. For List, you can use the add(int index, Object element) method to add elements to the specified position.

2. Delete

Use the remove() method to delete elements in the container. For List, you can use the remove(int index) method to delete the element at the specified position.

3. Query

Use the get() method to get the elements in the container. For List, you can use the get(int index) method to get the element at the specified position.

4. Insertion

Use the add(int index, Object element) method to insert the element into the specified position.

5. Determine whether the element exists

Use the contains() method to determine whether the element exists in the container.

4. How to implement containers

Java containers are implemented in an object-oriented manner. The underlying corresponding data structures include lists, hash tables, trees, etc. Among them, hash tables and trees are more efficient than lists.

In Java5 and later versions, the generic mechanism and automatic boxing and unboxing mechanism are introduced. This way, we can use the container directly without the need for casts.

Summary:

Container technology in Java can greatly improve the efficiency and flexibility of programming. We can choose the appropriate container implementation based on actual needs to better process data. However, when using containers, we need to pay attention to thread safety issues and flexibly choose specific implementation methods based on the actual situation.

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