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Convert java.util.Collection to java.util.List

· One min read
Sandeep Bhardwaj
List list;  
if (collection instanceof List)  
{  
  list = (List)collection;  
}  
else  
{  
  list = new ArrayList(collection);  
}

Generic way (java 1.5<=)

public <E> List<E> collectionToList(Collection<E> collection)  
 {  
  List<E> list;  
  if (collection instanceof List)  
  {  
   list = (List<E>) collection;  
  }  
  else  
  {  
   list = new ArrayList<E>(collection);  
  }  
  return list;  
 }

Without Generics (java 1.4>=)

public List collectionToList(Collection collection)  
 {  
  List list;  
  if (collection instanceof List)  
  {  
   list = (List) collection;  
  }  
  else  
  {  
   list = new ArrayList(collection);  
  }  
  return list;  
 }

How to convert java.util.List to java.util.Set

· One min read
Sandeep Bhardwaj

Removing duplicate items from a list is pretty simple in java just convert the list to java.util.Set it will automatically remove the duplicate items and create a set for you.

Syntax

Set<E> alphaSet  = new HashSet<E>(<your List>);

Example

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

public class ListToSet  
{  
 public static void main(String[] args)  
 {  
  List<String> alphaList = new ArrayList<String>();  
  alphaList.add("A");  
  alphaList.add("B");  
  alphaList.add("C");  
  alphaList.add("A");  
  alphaList.add("B");  
  System.out.println("List values .....");  
  for (String alpha : alphaList)  
  {  
   System.out.println(alpha);  
  }  
  Set<String> alphaSet = new HashSet<String>(alphaList);  
  System.out.println("\nSet values .....");  
  for (String alpha : alphaSet)  
  {  
   System.out.println(alpha);  
  }  
 }  
}