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Optional Collection operations

The following list shows the optional operations in the Collection interface. Each of these methods has the ability to modifythe contents of the collection.

  • add()
  • addAll()
  • clear()
  • remove()
  • removeAll()
  • retainAll()

Optional Map operations

The following list shows the optional operations in the Map interface. Each of these methods also has the ability to modify the contents ofthe map.

  • clear()
  • put()
  • putAll()
  • remove()

Many methods are not optional

In both cases, the interface declares numerous other methods that are not optional. Generally, the non-optional methods don't have the ability tomodify the collection. For example, the get method of the Map interface is not optional. Although the get method receives an incoming key and returns the value to which the key maps, the method doesn't have the ability to modify the contents of the collection.

Run the program

I encourage you to copy the code from Listing 1 and paste it into your Java editor. Thencompile and execute it.

Run the program and observe the results. Experiment with the code. Make changes, run the program again, and observe the results of your changes. Make certain that youcan explain why your changes behave as they do.


A collections framework contains at least the following items:

  • interfaces
  • implementations
  • algorithms

The Java Collections Framework defines eight core interfaces, in two distinct trees. One tree is rooted in Collection and the other is rooted in Map .

The basic purpose of the core interfaces is to make it possible for collections to be manipulated without regard for how they are implemented, solong as the implementation satisfies the contracts of the interfaces.

When the same method name (and signature) is called on references to collections of different types, the behavior of the method is likely to be different for each collection.However, in each case, that behavior will be appropriate for the type of collection object on which the method is called. This is polymorphicbehavior.

Six of the methods declared in the Collection interface are optional insofar as being supported by implementing classes is concerned. The optional methodsall have the ability to modify the contents of the collection. Those implementing classes that don't support an optional method must throw an UnsupportedOperationException if that method is called on an object of the class. Similarly four of the methods declared in the Map interface are optional.

Many methods declared in the Collection interface are not optional. Generally, the non-optional methods don't have the ability to modify thecollection.

What's next?

In the next module, I will discuss and illustrate some of the details of the core interfaces and the general-purpose implementations in the Java CollectionsFramework. For example, I will discuss the difference between a set and a list . I will also discuss the difference between ordered and sorted . I will discuss the fact that additional stipulations are applied as you progressdown the framework interface hierarchy. In order to help you learn and retain the material, I will provide a couple of short quizzes.


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java4050: Core Collection Interfaces
  • File: Java4050.htm
  • Published: 04/18/13

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.


Questions & Answers

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Eke Reply
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Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
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RAW Reply
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I think
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Brian Reply
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Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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Bob Reply
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Smarajit Reply
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