Java Collections newSetFromMap() Method with Examples

by Online Tutorials Library July 22, 2022

Java Collections newSetFromMap() Method

The newSetFromMap() method of Java Collections class is used to return a set backed by the specified map. The resulting set displays the same ordering, concurrency, and performance characteristics as the backing map.

Syntax

Following is the declaration of newSetFromMap() method:

Parameter

Parameter	Description	Required/Optional
map	It is the backing map.	Required

Returns

The newSetFromMap() method returns the set backed by the specified map.

Exceptions

IllegalArgumentException– It throws this exception if map is not empty.

Compatibility Version

Java 1.6 and above

Example 1

  import java.util.*;  public class CollectionsNewSetFromMapExample1 {  public static void main(String[] args) {  // create map        Map map = new WeakHashMap();        // create a set from map        Set set = Collections.newSetFromMap(map);         // add values in set        set.add(“Raj”);         set.add(“Rahul”);        set.add(“Karan”);        // set and map values are        System.out.println(“Set is: ” + set);        System.out.println(“Map is: ” + map);        }  }  ,>,>

Test it Now

Output:

Set is: [Karan, Raj, Rahul]  Map is: {Karan=true, Raj=true, Rahul=true}

Example 2

  import java.util.*;  public class CollectionsNewSetFromMapExample2 {  public static void main(String[] args) {  Map map = new IdentityHashMap();        Set set = Collections.newSetFromMap(map);        set.add(1);        set.add(1);        set.add(1);        // set and map values are  System.out.println(“Set is: ” + set);  System.out.println(“Map is: ” + map);        }  }  ,>,>

Test it Now

Output:

Set is: [1]  Map is: {1=true}

Example 3

  import java.util.*;  import java.util.concurrent.ConcurrentHashMap;  public class CollectionsNewSetFromMapExample3 {  public static void main(String[] args) {  Set users = Collections.newSetFromMap(new ConcurrentHashMap());              System.out.println(“Users: ” + users);              users.add(“Java”);              users.add(“PHP”);              System.out.println(“Users: ” + users);        }  }  ,>

Test it Now

Output:

Users: []  Users: [Java, PHP]

Next TopicJava Collections Class

addAll()asLifoQueue()binarySearch()checkedCollection()CheckedMap()checkedQueue()checkedSet()collections copy()disjoint()emptyEnumeration()fill()java list max min reverse sort synchronizedMap()

Java Collections newSetFromMap() Method with Examples

Java Collections newSetFromMap() Method

Syntax

Parameter

Returns

Exceptions

Compatibility Version

Example 1

Example 2

Example 3

Java Convert boolean to String

Java Collections swap() Method with Examples

You may also like