2020 New Java Interview Questions - Containers (1)

1. What are the java containers?

Illustration of commonly used containers:

2. What is the difference between Collection and Collections?

java.util.Collection is a collection interface (a top-level interface of the collection class). It provides common interface methods for basic operations on collection objects. The Collection interface has many specific implementations in the Java class library. The significance of the Collection interface is to provide a maximum unified operation method for various specific collections. Its directly inherited interfaces include List and Set.

Collections is a tool class/helper class of the collection class, which provides a series of static methods for various operations such as sorting, searching, and thread safety of elements in the collection.

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3. What is the difference between List, Set, and Map?

4. What is the difference between HashMap and Hashtable?

hashMap removes the contains method of HashTable, but adds containsValue() and containsKey() methods.

HashTable is synchronous, while HashMap is asynchronous, and the efficiency is higher than hashTable.

HashMap allows empty key values, but hashTable does not.

5. How to decide whether to use HashMap or TreeMap?

For operations such as inserting, deleting and locating elements in Map, HashMap is the best choice. However, if you need to iterate over an ordered collection of keys, TreeMap is a better choice. Depending on the size of your collection, it may be faster to add elements to a HashMap and replace the map with a TreeMap for ordered key traversal.

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