A package is a group of similar types of classes, interfaces and sub-packages. Package can be categorized in two form, built-in package and user-defined package. There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc. Here, we will have the detailed learning of creating and using user-defined packages.
An interface is a blueprint of a class. It has static constants and abstract methods. The interface is a mechanism to achieve fully abstraction in java. There can be only abstract methods in the interface. It is used to achieve fully abstraction and multiple inheritance in Java. Interface also represents IS-A relationship.
The instanceof operator is used to test whether the object is an instance of the specified type (class or subclass or interface). The instanceof operator is also known as type comparison operator because it compares the instance with type. It returns either true or false.
Connecting a method call to the method body is known as binding. There are two types of binding static binding (also known as early binding). dynamic binding (also known as late binding). Understanding Type Let's understand the type of instance. 1) variables have a type Each variable has a type, it may be primitive and non-primitive.
The final keyword in java is used to restrict the user. The final keyword can be used in many context. Final can be: variable method class The final keyword can be applied with the variables, a final variable that have no value it is called blank final variable or uninitialized final variable.
The covariant return type specifies that the return type may vary in the same direction as the subclass. Before Java5, it was not possible to override any method by changing the return type. But now, since Java5, it is possible to override method by changing the return type if subclass overrides any method whose return type is Non-Primitive but it changes its return type to subclass type.
Having the same method in the subclass as declared in the parent class is known as method overriding. In other words, If subclass provides the specific implementation of the method i.e. already provided by its parent class, it is known as Method Overriding.
Advantage of OOPs Naming Convention Object and Class Method Overloading Constructor static keyword this keyword Inheritance(IS-A) Aggregation(HAS-A) Method Overriding Covariant Return Type super keyword Instance Initializer block final keyword Runtime Polymorphism Dynamic Binding instanceof operator Abstract class Interface Package Access Modifiers Encapsulation Object class Object Cloning Java Array Call By Value strictfp keyword API Document Command Line Arg
Advantage of OOPs Naming Convention Object and Class Method Overloading Constructor static keyword this keyword Inheritance(IS-A) Aggregation(HAS-A) Method Overriding Covariant Return Type super keyword Instance Initializer block final keyword Runtime Polymorphism Dynamic Binding instanceof operator Abstract class Interface Package Access Modifiers Encapsulation Object class Object Cloning Java Array Call By Value strictfp keyword API Document Command Line Arg
Advantage of OOPs Naming Convention Object and Class Method Overloading Constructor static keyword this keyword Inheritance(IS-A) Aggregation(HAS-A) Method Overriding Covariant Return Type super keyword Instance Initializer block final keyword Runtime Polymorphism Dynamic Binding instanceof operator Abstract class Interface Package Access Modifiers Encapsulation Object class Object Cloning Java Array Call By Value strictfp keyword API Document Command Line Arg
There is only call by value in java, not call by reference. If we call a method passing a value, it is known as call by value. The changes being done in the called method, is not affected in the calling method.
Normally, array is a collection of similar type of elements that have contigious memory location. In java, array is an object the contains elements of similar data type. It is a data structure where we store similar elements. We can store only fixed elements in an array.
A class that is declared with abstract keyword, is known as abstract class. Before learning abstract class, let's understand the abstraction first. Abstraction Abstraction is a process of hiding the implementation details and showing only functionality to the user.
Constructor is a special type of method that is used to initialize the object. Constructor is invoked at the time of object creation. It constructs the values i.e. provides data for the object that is why it is known as constructor. Rules for creating constructor There are basically two rules defined for the constructor.
