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In software, a data access object (DAO) is a pattern that provides an abstract interface to some type of database or other persistence mechanism. By mapping application calls to the persistence layer, the DAO provides data operations without exposing database details. This isolation supports the single responsibility principle.
Java Data Objects (JDO) is a specification of Java object persistence. One of its features is a transparency of the persistence services to the domain model . JDO persistent objects are ordinary Java programming language classes ( POJOs ); there is no requirement for them to implement certain interfaces or extend from special classes.
Classes may inherit from other classes, so they are arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names.
In class-based programming, inheritance is done by defining new classes as extensions of existing classes: the existing class is the parent class and the new class is the child class. If a child class has only one parent class, this is known as single inheritance , while if a child class can have more than one parent class, this is known as ...
Classes can be derived from one or more existing classes, thereby establishing a hierarchical relationship between the derived-from classes (base classes, parent classes or superclasses) and the derived class (child class or subclass) . The relationship of the derived class to the derived-from classes is commonly known as an is-a relationship. [21]
Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (), [16] meaning that compiled Java code can run on all platforms that support Java without the need to recompile. [17]
If a class does not specify its superclass, it implicitly inherits from java.lang.Object class. Thus all classes in Java are subclasses of Object class. If the superclass does not have a constructor without parameters the subclass must specify in its constructors what constructor of the superclass to use. For example:
In object-oriented programming, the template method is one of the behavioral design patterns identified by Gamma et al. [1] in the book Design Patterns.The template method is a method in a superclass, usually an abstract superclass, and defines the skeleton of an operation in terms of a number of high-level steps.