AbstractSet Class in Java with Examples

The AbstractSet class in Java is a part of the Java Collection Framework which implements the Collection interface and extends the AbstractCollection class. It provides a skeletal implementation of the Set interface. This class does not override any of the implementations from the AbstractCollection class, but merely adds implementations for equals() and hashCode() method.

Class Hierarchy:

java.lang.Object
 ↳ java.util.AbstractCollection<E>
    ↳ Class AbstractSet<E>

Syntax:

public abstract class AbstractSet<E>
  extends AbstractCollection<E>
     implements Set<E>

Where E is the type of elements maintained by 
this Set.

Constructors in Java AbstractSet:

protected AbstractSet(): The default constructor, but being protected, it doesn’t allow to create an AbstractSet object.

Below is a sample program to illustrate the java AbstractSet:

// Java code to illustrate AbstractSet 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] args) throws Exception 
    { 
  
        try { 
  
            // Creating object of AbstractSet<Integer> 
            AbstractSet<Integer> 
                abs_set = new TreeSet<Integer>(); 
  
            // Populating abs_set 
            abs_set.add(1); 
            abs_set.add(2); 
            abs_set.add(3); 
            abs_set.add(4); 
            abs_set.add(5); 
  
            // print abs_set 
            System.out.println("AbstractSet: "
                               + abs_set); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
    } 
} 

Output:

AbstractSet: [1, 2, 3, 4, 5]

Methods in Java AbstractSet:

equals(Object o): Compares the specified object with this set for equality.
hashCode(): Returns the hash code value for this set.
removeAll(Collection c): Removes from this set all of its elements that are contained in the specified collection (optional operation).

Example:

// Java code to illustrate 
// methods of AbstractSet 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] args) throws Exception 
    { 
  
        try { 
  
            // Creating object of AbstractSet<Integer> 
            AbstractSet<Integer> 
                abs_set = new TreeSet<Integer>(); 
  
            // Populating abs_set 
            abs_set.add(1); 
            abs_set.add(2); 
            abs_set.add(3); 
            abs_set.add(4); 
            abs_set.add(5); 
  
            // print abs_set 
            System.out.println("AbstractSet before "
                               + "removeAll() operation : "
                               + abs_set); 
  
            // Creating another object of ArrayList<Integer> 
            Collection<Integer> 
                arrlist2 = new ArrayList<Integer>(); 
            arrlist2.add(1); 
            arrlist2.add(2); 
            arrlist2.add(3); 
  
            // print arrlist2 
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrlist2); 
  
            // Removing elemnts from AbstractSet 
            // specified in arrlist2 
            // using removeAll() method 
            abs_set.removeAll(arrlist2); 
  
            // print arrlist1 
            System.out.println("AbstractSet after "
                               + "removeAll() operation : "
                               + abs_set); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
} 

Output:

AbstractSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
AbstractSet after removeAll() operation : [4, 5]

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/AbstractSet.html

AbstractSet Class in Java with Examples

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