Detailed explanation of conversion between list, set and array in JAVA

JAVA’s conversion between list, set, and array mainly uses Apache Jakarta Commons Collections. The specific method is as follows:
import org.apache.commons.collections.CollectionUtils;

String[ ] strArray = {"aaa", "bbb", "ccc"};
List strList = new ArrayList();
Set strSet = new HashSet();
CollectionUtils.addAll(strList, strArray) ;
CollectionUtils.addAll(strSet, strArray);
The implementation of the CollectionUtils.addAll() method is very simple, it just uses the add() method of Collection in a loop.

If you just want to convert an array into a List, you can use the java.util.Arrays class in the JDK:

import java.util.Arrays;

String[] strArray = {"aaa", "bbb", "ccc"};
List strList = Arrays.asList(strArray);
However, the List returned by the Arrays.asList() method cannot add objects because of the implementation of this method It is an ArrayList that is new using the size of the array referenced by the parameter.

★ Collection to Array
Use Collection's toArray() method directly, which has two overloaded versions:

Object[] toArray();
T[] toArray(T[] a);

★ Map to Collection
Use Map’s values() method directly.

★ List and Set conversion
List list = new ArrayList(new Hashset());// Fixed-size list
List list = Arrays.asList(array);//Growable
list list = new LinkedList(Arrays.asList(array));// Duplicate elements are discarded
Set set = new HashSet(Arrays.asList(array));

More lists in JAVA, For detailed information on conversion between set and arrays, please pay attention to the PHP Chinese website!