Collection Interface

The Collection interface (java.util.Collection) is one of the root interfaces of the Java collection classes. It declares the core methods that all collections will have. Because all collections implement Collection interface, so we might familiar with its methods for a clear understanding of the framework.

The following shows the Collection interface:

public interface Collection<E> extends Iterable<E> {
    // Basic operations
    int size();
    boolean isEmpty();
    boolean contains(Object element);
    // optional
    boolean add(E element);
    // optional
    boolean remove(Object element);
    Iterator<E> iterator();

    // Bulk operations
    boolean containsAll(Collection<?> c);
    // optional
    boolean addAll(Collection<? extends E> c); 
    // optional
    boolean removeAll(Collection<?> c);
    // optional
    boolean retainAll(Collection<?> c);
    // optional
    void clear();

    // Array operations
    Object[] toArray();
    <T> T[] toArray(T[] a);
}

Following table specifies the public methods of collection interface:

Example:

package com.sample.javase.testing;

import java.util.ArrayList;

import java.util.Collection;

public class CollectionInterfaceExample {

/**

* @param args

*/

public static void main(String[] args) {

Collection<String> collection = new ArrayList<String>();

collection.add("javase");

collection.add("javaee");

collection.add("javame");

//We can print the collection as follows or we can iterate the collection.

System.out.println(collection);

}

}