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.
// Java program to demonstrate conversion of // list to set using simple traversal import java.util.*;
class Test {
public static void main(String[] args)
{
// Creating a list of strings
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);
// We can created TreeSet same way
}
} |
Method 2 (Using HashSet or TreeSet Constructor)
// Java program to demonstrate conversion of // list to set using constructor import java.util.*;
class Test {
public static void main(String[] args)
{
// Creating a list of strings
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
// Creating a hash set using constructor
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)
// Java program to demonstrate conversion of // Set to array using addAll() method. import java.util.*;
class Test {
public static void main(String[] args)
{
// Creating a list of strings
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);
}
} |
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.
// Java program to demonstrate conversion of // Set to list using stream import java.util.*;
import java.util.stream.*;
class Test {
public static void main(String[] args)
{
// Creating a list of strings
List<String> aList = Arrays.asList( "Geeks" , "for" ,
"GeeksQuiz" , "GeeksforGeeks" , "GFG" );
// Converting to set using stream
Set<String> set = aList.stream().collect(Collectors.toSet());
for (String x : set)
System.out.println(x);
}
} |