Java Set is a part of java.util package and extends java.util.Collection interface. It does not allow the use of duplicate elements and at max can accommodate only one null element. Few important features of Java Set interface are as follows:
- The set interface is an unordered collection of objects in which duplicate values cannot be stored.
- The Java Set does not provide control over the position of insertion or deletion of elements.
- Basically, Set is implemented by HashSet, LinkedHashSet or TreeSet (sorted representation).
- Set has various methods to add, remove clear, size, etc to enhance the usage of this interface.
In this post different methods to convert a List interface to Set in Java is discussed:
- Naive Approach: The naive solution is to create an empty set and add every element of the specified list to the newly created set.
Below is the implementation of the naive approach:
// Java Program to convert
// List to Set in Java 8
import
java.util.*;
import
java.util.stream.*;
import
java.util.function.Function;
class
GFG {
// Generic function to convert list to set
public
static
<T> Set<T> convertListToSet(List<T> list)
{
// create an empty set
Set<T> set =
new
HashSet<>();
// Add each element of list into the set
for
(T t : list)
set.add(t);
// return the set
return
set;
}
public
static
void
main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList(
"GeeksForGeeks"
,
"Geeks"
,
"forGeeks"
,
"A computer portal"
,
"for"
,
"Geeks"
);
// Print the List
System.out.println(
"List: "
+ list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println(
"Set from List: "
+ set);
}
}
chevron_rightfilter_noneOutput:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
- Using Constructor: HashSet constructor can take another collection object to construct a new set containing the elements of the specied list.
Below is the implementation of the above approach:
// Java Program to convert
// List to Set in Java 8
import
java.util.*;
import
java.util.stream.*;
class
GFG {
// Generic function to convert list to set
public
static
<T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List
return
new
HashSet<>(list);
}
public
static
void
main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList(
"GeeksForGeeks"
,
"Geeks"
,
"forGeeks"
,
"A computer portal"
,
"for"
,
"Geeks"
);
// Print the List
System.out.println(
"List: "
+ list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println(
"Set from List: "
+ set);
}
}
chevron_rightfilter_noneOutput:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
- Using Java 8 Stream API: HashSet constructor can take another collection object to construct a new set containing the elements of the specied list.
Below is the implementation of the above approach:
// Java Program to convert
// List to Set in Java 8
import
java.util.*;
import
java.util.stream.*;
class
GFG {
// Generic function to convert list to set
public
static
<T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List
return
list.stream().collect(Collectors.toSet());
}
public
static
void
main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList(
"GeeksForGeeks"
,
"Geeks"
,
"forGeeks"
,
"A computer portal"
,
"for"
,
"Geeks"
);
// Print the List
System.out.println(
"List: "
+ list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println(
"Set from List: "
+ set);
}
}
chevron_rightfilter_noneOutput:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
- Using Guava Sets.newHashSet(): Sets.newHashSet() creates a mutable HashSet instance containing the elements of the specified list.
Below is the implementation of the above approach:
// Java Program to convert
// List to Set in Java 8
import
java.util.*;
import
java.util.stream.*;
class
GFG {
// Generic function to convert list to set
public
static
<T> Set<T> convertListToSet(List<T> list)
{
// create a set from the List
return
return
Sets.newHashSet(list);
}
public
static
void
main(String args[])
{
// Create a stream of integers
List<String> list = Arrays.asList(
"GeeksForGeeks"
,
"Geeks"
,
"forGeeks"
,
"A computer portal"
,
"for"
,
"Geeks"
);
// Print the List
System.out.println(
"List: "
+ list);
// Convert List to stream
Set<String> set = convertListToSet(list);
// Print the Set
System.out.println(
"Set from List: "
+ set);
}
}
chevron_rightfilter_noneOutput:
List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
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