List to Set in Java
Last Updated :
11 Dec, 2018
Given a list (ArrayList or LinkedList), convert it into a set (HashSet or TreeSet) of strings in Java.
Method 1 (Simple)
We simply create an list. We traverse the given set and one by one add elements to the list.
import java.util.*;
class Test {
public static void main(String[] args)
{
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
Set<String> hSet = new HashSet<String>();
for (String x : aList)
hSet.add(x);
System.out.println( "Created HashSet is" );
for (String x : hSet)
System.out.println(x);
}
}
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Method 2 (Using HashSet or TreeSet Constructor)
import java.util.*;
class Test {
public static void main(String[] args)
{
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
Set<String> hSet = new HashSet<String>(aList);
System.out.println( "Created HashSet is" );
for (String x : hSet)
System.out.println(x);
System.out.println( "Created TreeSet is" );
Set<String> tSet = new TreeSet<String>(aList);
System.out.println( "Created TreeSet is" );
for (String x : tSet)
System.out.println(x);
}
}
|
Method 3 (Using addAll method)
import java.util.*;
class Test {
public static void main(String[] args)
{
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
Set<String> hSet = new HashSet<String>(aList);
hSet.addAll(aList);
System.out.println( "Created HashSet is" );
for (String x : hSet)
System.out.println(x);
Set<String> tSet = new TreeSet<String>(aList);
tSet.addAll(aList);
System.out.println( "Created TreeSet is" );
for (String x : tSet)
System.out.println(x);
}
}
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Method 4 (Using stream in Java)
We use stream in Java to convert given list to stream, then stream to set. This works only in Java 8 or versions after that.
import java.util.*;
import java.util.stream.*;
class Test {
public static void main(String[] args)
{
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
Set<String> set = aList.stream().collect(Collectors.toSet());
for (String x : set)
System.out.println(x);
}
}
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