Java Collection Framework overview
Java Collections are used in every programming language and initial java release contained few classes for collections: Vector, Stack, Hashtable, Array. But looking at the larger scope and usage, Java 1.2 came up with Collections Framework that group all the collections interfaces, implementations and algorithms.
Java Collections have come through a long way with usage of Generics and Concurrent Collection classes for thread-safe operations. It also includes blocking interfaces and their implementations in java concurrent package.
Some of the benefits of collections framework are:
- Reduced development effort by using core collection classes rather than implementing our own collection classes.
- Code quality is enhanced with the use of well tested collections framework classes.
- Reduced effort for code maintenance by using collection classes shipped with JDK.
- Reusability and Interoperability
What is the benefit of Generics in Collections Framework?
Java 1.5 came with Generics and all collection interfaces and implementations use it heavily. Generics allow us to provide the type of Object that a collection can contain, so if you try to add any element of other type it throws compile time error.
This avoids ClassCastException at Runtime because you will get the error at compilation. Also Generics make code clean since we don’t need to use casting and instanceofoperator. It also adds up to runtime benefit because the bytecode instructions that do type checking are not generated.
What are the basic interfaces of Java Collections Framework?
Collection is the root of the collection hierarchy. A collection represents a group of objects known as its elements. The Java platform doesn’t provide any direct implementations of this interface.
Set is a collection that cannot contain duplicate elements. This interface models the mathematical set abstraction and is used to represent sets, such as the deck of cards.
List is an ordered collection and can contain duplicate elements. You can access any element from it’s index. List is more like array with dynamic length.
A Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value.
Some other interfaces are Queue, Dequeue, Iterator, SortedSet, SortedMap and ListIterator.
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