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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);
}
}
}