What is the difference between list and set in Java?

The differences between the list and set methods are: 1. List can insert multiple null elements, while set only allows one null element to be inserted; 2. The list container is ordered, while the set container is unordered; 3. The list method allows duplicate objects, but the set method does not allow duplicate objects, etc.

The differences between the list and set methods are: list can allow duplicate objects and insert multiple null values, but set does not allow it; list containers are ordered, The set container is unordered, etc.

Collections in Java include three major categories, namely Set, List and Map. They are all in java.util and are interfaces. Each of them has its own implementation class. The implementation classes of Set mainly include HashSet and TreeSet, and the implementation classes of List mainly include ArrayList. Next, I will introduce to you the differences between these two categories, which will serve as a reference and I hope it will be helpful to you.

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The difference between the List method and the set method

(1) Duplicate objects

The list method can allow duplicate objects, but the set method does not Duplicate objects are allowed

(2) null elements

list can insert multiple null elements, while set only allows the insertion of one null element

(3) Whether the container is ordered

list is an ordered container that maintains the insertion order of each element. That is, the output order is the input order, and the set method is an unordered container, which cannot guarantee the storage order of each element. TreeSet maintains a sorting order through Comparator or Comparable

(4) Commonly used implementation classes

Commonly used implementation classes for list methods include ArrayList, LinkedList and Vector. Among them, ArrayList is the most popular, which provides random access using indexes, while LinkedList is more suitable for situations where elements often need to be added or removed from the List. Vector represents the underlying array and is the most thread-safe

Set method. Several popular implementation classes are HashSet, LinkedHashSet and TreeSet. The most popular is HashSet implemented based on HashMap; TreeSet also implements the SortedSet interface, so TreeSet is an ordered container that is sorted according to the definition of compare() and compareTo()

Summary: The above is the entire content of this article. I hope this article can help everyone distinguish the difference between list and set.

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