Abstract Collection in Java with Examples

public abstract class AbstractCollection<E>
    extends Object
       implements Collection<E>

where E is the type of elements maintained
by this collection.

Constructors in Java AbstractCollection:

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

Below is the sample program to illustrate AbstractCollection in Java:

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// Java code to illustrate AbstractCollection

import java.util.*;

import java.util.AbstractCollection;

public class GFG {

public static void main(String[] args)

{

// Create an empty collection

AbstractCollection<Object>

abs = new ArrayList<Object>();

// Use add() method to add

// elements in the collection

abs.add("Welcome");

abs.add("To");

abs.add("Geeks");

abs.add("4");

abs.add("Geeks");

// Displaying the Collection

System.out.println("AbstractCollection: "

+ abs);

}

Output:

AbstractCollection: [Welcome, To, Geeks, 4, Geeks]

Methods in Java Abstract Collection:

add(E e): This method ensures that this collection contains the specified element (optional operation).
addAll(Collection c): This method Adds all of the elements in the specified collection to this collection (optional operation).
clear(): This method removes all of the elements from this collection (optional operation).
contains(Object o): This method returns true if this collection contains the specified element.
contains(Collection c): This method returns true if this collection contains all of the elements in the specified collection.
isEmpty(): This method returns true if this collection contains no elements.
iterator(): This method returns an iterator over the elements contained in this collection.
remove(Object o): This method removes a single instance of the specified element from this collection if it is present (optional operation).
size(): This method returns the number of elements in this collection.
toArray(): This method returns an array containing all of the elements in this collection.
toArray(T[] a): This method returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
toString?(): This method returns a string representation of this collection.

Example:

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// Java code to illustrate

// methods of AbstractCollection

import java.util.*;

import java.util.AbstractCollection;

public class AbstractCollectionDemo {

public static void main(String args[])

{

// Creating an empty collection

AbstractCollection<String>

abs1 = new TreeSet<String>();

// Use add() method to add

// elements into the Collection

abs1.add("Welcome");

abs1.add("To");

abs1.add("Geeks");

abs1.add("4");

abs1.add("Geeks");

abs1.add("TreeSet");

// Displaying the Collection

System.out.println("AbstractCollection 1: "

+ abs1);

// Creating anothe Collection

AbstractCollection<String>

abs2 = new TreeSet<String>();

// Displaying the Collection

System.out.println("AbstractCollection 2: "

+ abs2);

// Using addAll() method to Append

abs2.addAll(abs1);

// Displaying the Collection

System.out.println("AbstractCollection 2: "

+ abs2);

// Clearing the collection

// using clear() method

abs1.clear();

// Check for the empty collection

System.out.println("Is the collection empty? "

+ abs1.isEmpty());

}

Output:

AbstractCollection 1: [4, Geeks, To, TreeSet, Welcome]
AbstractCollection 2: []
AbstractCollection 2: [4, Geeks, To, TreeSet, Welcome]
Is the collection empty? true

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

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