![]() HashMap is the implementation of Map, but it doesn't maintain any order. HashMap and LinkedHashMap allow null keys and values, but TreeMap doesn't allow any null key or value.Ī Map can't be traversed, so you need to convert it into Set using keySet() or entrySet() method. The hierarchy of Java Map is given below:Ī Map doesn't allow duplicate keys, but you can have duplicate values. There are two interfaces for implementing Map in java: Map and SortedMap, and three classes: HashMap, LinkedHashMap, and TreeMap. A Map contains unique keys.Ī Map is useful if you have to search, update or delete elements on the basis of a key. Each key and value pair is known as an entry. The same goes for new algorithms that operate on objects that implement these interfaces.A map contains values on the basis of key, i.e. Fosters software reuse: New data structures that conform to the standard collection interfaces are by nature reusable.Designers and implementers don't have to reinvent the wheel each time they create an API that relies on collections instead, they can use standard collection interfaces. Reduces effort to design new APIs: This is the flip side of the previous advantage.With the advent of standard collection interfaces, the problem went away. There was little consistency among these ad hoc collections sub-APIs, so you had to learn each one from scratch, and it was easy to make mistakes when using them. In the past, each such API had a small sub-API devoted to manipulating its collections. Reduces effort to learn and to use new APIs: Many APIs naturally take collections on input and furnish them as output.If my network administration API furnishes a collection of node names and if your GUI toolkit expects a collection of column headings, our APIs will interoperate seamlessly, even though they were written independently. Allows interoperability among unrelated APIs: The collection interfaces are the vernacular by which APIs pass collections back and forth.Because you're freed from the drudgery of writing your own data structures, you'll have more time to devote to improving programs' quality and performance. The various implementations of each interface are interchangeable, so programs can be easily tuned by switching collection implementations. Increases program speed and quality: This Collections Framework provides high-performance, high-quality implementations of useful data structures and algorithms.By facilitating interoperability among unrelated APIs, the Java Collections Framework frees you from writing adapter objects or conversion code to connect APIs. Reduces programming effort: By providing useful data structures and algorithms, the Collections Framework frees you to concentrate on the important parts of your program rather than on the low-level "plumbing" required to make it work.The Java Collections Framework provides the following benefits: ![]() Benefits of the Java Collections Framework We believe that the Java Collections Framework breaks with this tradition, as you will learn for yourself in this chapter. Historically, collections frameworks have been quite complex, which gave them a reputation for having a steep learning curve. In essence, algorithms are reusable functionality.Īpart from the Java Collections Framework, the best-known examples of collections frameworks are the C++ Standard Template Library (STL) and Smalltalk's collection hierarchy. The algorithms are said to be polymorphic: that is, the same method can be used on many different implementations of the appropriate collection interface.
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