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Java Tutorial » Collections » Collections Framework  
9.1.4.Conversion of different Collection data typesPrevious/Next

Implementations of the Collection interface normally have a constructor that accepts a Collection object. This enables you to convert a Collection to a different type of Collection, such as a Queue to a List, or a List to a Set, etc. Here are the constructors of some implementations:

public ArrayList (Collection c)
     public HashSet (Collection c)
     public LinkedList (Collection c)

As an example, the following code converts a Queue to a List.

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class MainClass {

  public static void main(String[] args) {
    Queue queue = new LinkedList();
    queue.add("Hello");
    queue.add("World");
    List list = new ArrayList(queue);

    System.out.println(list);
  }

}
[Hello, World]

And this converts a List to a Set.

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class MainClass {

  public static void main(String[] args) {
    List myList = new ArrayList();
    myList.add("Hello");
    myList.add("World");
    myList.add("World");
    Set set = new HashSet(myList);

    System.out.println(set);
  }

}
[World, Hello]
9.1.Collections Framework
9.1.1. The Collections Framework consists of three parts
9.1.2. Framework Interfaces
9.1.3. Interface type and its implementation
9.1.4. Conversion of different Collection data types
9.1.5. Making Your Objects Comparable and Sortable
9.1.6. Using Comparable and Comparator
9.1.7. Deep clone collection: Returns a new collection containing clones of all the items in the specified collection.