Implementation principles of collection classes in Java language

The collection class in Java language is a set of data structures used to store and operate objects. These collection classes provide a more convenient and flexible way to deal with a series of objects, with efficient, safe and reliable features. In this article, we will delve into the implementation principles of Java collection classes.

Java collection classes are mainly divided into two types: one is a collection class implemented based on arrays, and the other is a collection class implemented based on linked lists.

1. Collection class based on array implementation

The array in Java language is a linear data structure of limited length, composed of elements of the same data type. Collection classes implemented based on arrays occupy continuous space in memory. This implementation provides fast random access, but does not allow fast insertion or deletion of elements.

ArrayList in Java is a collection class based on array implementation. In ArrayList, elements are stored in the order of insertion. An array is initially created with a default size. When adding elements to ArrayList, if the array is full, you need to create a new array and replace the elements in the original array. The elements are copied into the new array. Although this will cause a certain performance loss, it can ensure higher efficiency when inserting elements. At the same time, because arrays are stored continuously, elements can be quickly accessed through array subscripts.

Another collection class implemented based on arrays is ArrayDeque in Java. In ArrayDeque, the underlying data structure that stores elements is a double-ended circular array. It is scalable and can automatically expand or shrink the size of the array when needed. At the same time, since the underlying array is a double-ended loop, you only need to move the pointer forward or backward when adding or removing elements, and there is no need to perform a large number of copy operations like ArrayList. This makes ArrayDeque more efficient when adding or removing elements.

2. Collection class implemented based on linked list

The linked list in Java language is a dynamic data structure composed of several nodes. Each node contains data and a pointer. Pointer to the next node. The advantage of a linked list is that it can quickly insert or delete elements, but it cannot provide fast random access.

LinkedList in Java is a collection class based on linked list implementation. In a LinkedList, each node contains the value of the current element and a pointer to the next element. When adding or deleting elements, you only need to change the pointing of the pointers between nodes. Since LinkedList is a linked list structure, accessing elements is inefficient and requires traversing the entire linked list.

Another collection class implemented based on linked list is LinkedHashMap in Java. In LinkedHashMap, elements are stored in insertion order or access order. The underlying data structure is a doubly linked list and a hash table. The hash table is used to quickly locate elements, and the doubly linked list is used to maintain the order of elements. This can not only quickly access elements, but also ensure that the insertion order or access order of elements remains unchanged.

In summary, the implementation principles of Java collection classes include two implementation methods: array-based and linked-list-based. Array-based collection classes provide fast random access to elements, but are less efficient when adding or removing elements. The linked list-based collection class provides the feature of quickly adding or deleting elements, but the efficiency of accessing elements is low. In actual programming, we need to choose the appropriate collection class as needed to improve the performance and efficiency of the program.

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