List Interface represents an ordered or sequential collection of objects.That means these methods will be available in all collection types which are inherited from Collection interface. ( forEach() and spliterator() methods are added to this interface from Java 8). Iterable interface has only one method called iterator() which returns an Iterator object, using that object you can iterate over the elements of Collection. Iterable interface is a member of java.lang package which is extended by interface which is nothing but the root level interface of the Java collection framework. That’s why Map doesn’t inherit Collection interface. Collection interface has the methods which support only the collection of values but not the collection of key-value pairs. Map is a collection of key-value pairs where as other collection types like List, Set and Queue are the collection of values. It is implemented by HashMap, LinkedHashMap and TreeMap.Ĥ) Explain the class hierarchy of Java collection framework?īelow diagram shows the class hierarchy of collection framework. It handles the group of objects as key-value pairs. Map : This is the one interface in Java Collection Framework which is not inherited from Collection interface. The major implementations of this interface are HashSet, LinkedHashSet and TreeSet. Set : It handles the group of objects which must contain only unique elements. LinkedList and PriorityQueue classes implement this interface. Queue : It handles the special group of objects in which elements are added from one end and removed from another end. ArrayList, Vector and LinkedList are the major implementation of this interface. List : It handles the sequential list of objects. In which all except Map are inherited from interface. The whole Java collection framework is divided into four interfaces – List, Queue, Set and Map. is the root level interface of the Java collection framework.ģ) What are the four main core interfaces of the Java collection framework? The collection framework is the answer to that.Ģ) What is the root level interface of the Java collection framework? Hence, there needed a central and unifying theme to handle the group of objects. The way you use Dictionary class is totally different from the way you use Stack class and the way you use Vector class is different from the way you use Properties class. But, each of them handle the objects differently. To overcome this drawback of arrays, Java collection framework is introduced in Java from JDK 1.2.Īlthough, there were classes like Dictionary, Vector, Stack and Properties which handle group of objects better than the arrays. This causes lots of problem while handling the group of objects. Size of the arrays can not be changed once they are defined. Earlier, arrays are used to store these group of objects. Java Collection Framework or simply collections are nothing but the group of objects stored in well defined manner. Using this collection framework, you can store the objects as a list or as a set or as a queue or as a map and perform operations like adding or removing or retrieving the objects without much hard work. Java Collection Framework provides some predefined classes and interfaces to handle the group of objects. Since Student doesn't override equals(), there are 5 objects in the HashSet.Java Collection Framework is a centralized and unified theme to store and manipulate the group of objects. What will be the result for below program? Poll() method removes the first element in queue and returns it, while peek() method returns the first element without removing it. PriorityQueue keeps elements sorted and it can have duplicates.Īdd() and offer() methods both offer same functionality. PriorityQueue pQueue = new PriorityQueue() What will be the output of following Java quiz on PriorityQueue ?

What will be output of following program ?ĪrralyList can contain duplicate elements.ĪrrayList remove() method only removes the first occurrence of a matching element. So, when add() is called, an exception is thrown. Arrays.asList() returns a fixed-size list backed by the specified array.

Java collections questions