Or test for all of the elements of the supplied collection. We’ll talk more aboutĪdditionally, the methods addAll(), removeAll(), and To step through the collection’s elements. This method returns an Iterator, which is an object you can use Use this method to examine all the elements in thisĬollection. This method returns true if this collection has no Use this method to find the number of elements in this This method returns true if the collection contains the If the object doesn’t exist in this collection,Ĭollections throw an UnsupportedOperationException if this Method, this method returns true if the object is removed from theĬollection. This method removes the specified object from this Throw an UnsupportedOperationException if this If the operation succeeds, this method returnsĮxists in this collection and the collection does not permitįurthermore, some collections are read-only. This method adds the supplied object to thisĬollection. Key/value pairs where the key can be used to retrieve the value in an Second, separate hierarchy is based on the Map interface, which represents a group of (and its descendants) represents a container that holds other objects. The Collections Framework is based around a handful of interfaces inĪre divided into two hierarchies. As we’ll see, all of the collections classes now take The combination of these newįeatures can significantly reduce the amount of code you write and add Primitive types means that you can generally treat objects and primitivesĪs equals where collections are concerned. Second, the introduction of autoboxing and unboxing of Possible for truly typesafe collections to be under the control of the First, the introduction of generic types,Īs we described in Chapter 8, has made it This all changed with the introduction of generic types andĪutoboxing of primitive values. The combination of these factors made code working with collections less Store it in a wrapper class first and unpack it later upon retrieving it. To put a number or other primitive type into a collection, you had to Issue was that, for practical reasons, collections could work only with Less a problem than it was just plain cumbersome and tedious. The face of Java’s compile-time type safety. Type cast every time you took an object out of a collection. The first was that-not having generic types to work with-collections wereīy necessity untyped and worked only with anonymous Objects instead of real types like Dates and Strings. Prior to Java 5, the Collections Framework had two major drawbacks. It can also save you from reinventing the Having these toolsĪt your disposal and understanding how to use them can make your code both Implement certain types of algorithms over collections. A great deal of basicĬomputer science is devoted to describing the most efficient ways to That lie at the heart of managing complex problems. Though conceptually simple, collections are one of the most powerful The older classes stillĮxist, but they have been retrofitted into the framework (with someĮccentricities) and are generally no longer used. Today, Java has a more comprehensive approach toĬollections called the Collections Framework. Which represents a dynamic list of objects, and the class, which holds a map of In theĮarly days, the Java platform had only two basic classes to address these ArraysĪlso do not represent abstract relationships between objects well. Of things that grow and shrink over the lifetime of an application. Static and because they have a fixed length, they are awkward for groups Level, Java supports collections in the form of arrays. Whenever we need to refer toĪ group of objects, we have some kind of collection. Are fundamental to all types of programming.
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