Collection class related issues in Java

The difference between collection and collections in 1,java

Java.util.Collection is a collection interface. It provides a common interface method for basic manipulation of collection objects. The collection interface has many specific implementations in the Java class Library. The meaning of the collection interface is to provide a maximum unified operation for a variety of specific collections.

Java.util.Collections is a wrapper class. It contains a variety of static polymorphic methods related to set operations. This class cannot be instantiated, just like a tool class that serves the Java collection framework.

2,list, Set, map inherit from collection interface?

List,set is map is not

The difference between 3,arraylist and vectors.

I. Synchronization: vector is thread-safe, that is, synchronous, and ArrayList is a thread program is not secure, not synchronous

Two. Data growth: When growth is needed, vectors grow by default to the original, while ArrayList is half the original

The difference between 4,hashmap and Hashtable

I. Historical reasons: Hashtable is based on the old dictionary class, HashMap is an implementation of the map interface introduced by Java 1.2

Two. Synchronization: Hashtable is thread-safe, that is, synchronous, and HashMap is a thread program is not secure, not synchronous

Three. Value: Only HashMap can let you use NULL as the key or value of an entry for a table

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Collection class related issues in Java