A class that is declared with abstract keyword, is known as abstract class in java. It can have abstract and non–abstract methods (method with body) Abstraction in Java Abstraction is a process of hiding the implementation details and showing only functionality to the user Abstraction lets you focus on what the object does instead of … Read more
In the early 1970s, the American National Standards Institute (ANSI) Standards Planning and Requirements Committee (SPARC) defined a framework for data modeling based on degrees of data abstraction. The ANSI/SPARC architecture (as it is often referred to) defines three levels of data abstraction: external, conceptual, and internal. You can use this framework to better understand … Read more
A bag is a container that stores a collection in which duplicate values are allowed. The items, each of which is individually stored, have no particular order but they must be comparable Bag(): Creates a bag that is initially empty. length (): Returns the number of items stored in the bag. Accessed using the len() … Read more
An abstract data type (or ADT) is a programmer-defined data type that specifies a set of data values and a collection of well-defined operations that can be performed on those values. Abstract data types are defined independent of their implementation, allowing us to focus on the use of the new data type instead of how … Read more
An abstraction is a mechanism for separating the properties of an object and restricting the focus to those relevant in the current context. The user of the abstraction does not have to understand all of the details in order to utilize the object, but only those relevant to the current task or problem. Two common … Read more
Timer and TimerTask work together. Timer is the class that you will use to schedule a task for execution. The task being scheduled must be an instance of TimerTask. Thus, to schedule a task, you will first create a TimerTask object and then schedule it for execution using an instance of Timer TimerTask implements the … Read more
The SimpleTimeZone class is a convenient subclass of TimeZone. It implements TimeZone’s abstract methods and allows you to work with time zones for a Gregorian calendar. It also computes daylight saving time. SimpleTimeZone defines four constructors. One is SimpleTimeZone(int timeDelta, String tzName) This constructor creates a SimpleTimeZone object. The offset relative to Greenwich mean time (GMT) is timeDelta. … Read more
EnumSet extends AbstractSet and implements Set. It is specifically for use with keys of an enum type. It is a generic class that has this declaration: Here, E specifies the elements. Notice that E must extend Enum, which enforces the requirement that the elements must be of the specified enum type. The Methods Defined by … Read more
Java SE 6 added the ArrayDeque class, which extends AbstractCollection and implements the Deque interface. It adds no methods of its own. ArrayDeque creates a dynamic array and has no capacity restrictions. (The Deque interface supports implementations that restrict capacity, but does not require such restrictions.) ArrayDeque is a generic class that has this declaration: … Read more
PriorityQueue extends AbstractQueue and implements the Queue interface. It creates a queue that is prioritized based on the queue’s comparator. PriorityQueue is a generic class that has this declaration: Here, E specifies the type of objects stored in the queue. PriorityQueues are dynamic, growing as necessary. PriorityQueue defines the six constructors shown here: The first constructor … Read more