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Java Articles
Page 27 of 450
How many ways are there to initialize the instance variables of a class in java?
You can initialize the instance variables of a class using final methods, constructors or, Instance initialization blocks.Final methodsWhenever you make a method final, you cannot override it. i.e. you cannot provide implementation to the superclass’s final method from the subclass.i.e. The purpose of making a method final is to prevent modification of a method from outside (child class). You can also use these final methods to initialize the instance variables.Exampleimport java.util.Scanner; public class FinalMethods { int age = getAge(); String name = getName(); static Scanner sc = new Scanner(System.in); public static final int getAge() { ...
Read MoreCan we change the access specifier from (public) while implementing methods from interface in Java?
An interface in Java is a specification of method prototypes. Whenever you need to guide the programmer or, make a contract specifying how the methods and fields of a type should be you can define an interface.To create an object of this type you need to implement this interface, provide a body for all the abstract methods of the interface and obtain the object of the implementing class.All the methods of the interface are public and abstract and, we will define an interface using the interface keyword as shown below −interface MyInterface{ public void display(); public void setName(String ...
Read MoreIs it possible to instantiate Type-parameter in Java?
Generics is a concept in Java where you can enable a class, interface and, method, accept all (reference) types as parameters. In other words it is the concept which enables the users to choose the reference type that a method, constructor of a class accepts, dynamically. By defining a class as generic you are making it type-safe i.e. it can act up on any datatype.Exampleclass Student { T age; Student(T age){ this.age = age; } public void display() { System.out.println("Value of age: "+this.age); } } public class GenericsExample { ...
Read MoreWhat happens if we overload default methods of an interface in java?
An interface in Java is similar to a class but, it contains only abstract methods and fields which are final and static.Since Java8 static methods and default methods are introduced in interfaces.Default methods − Unlike other abstract methods these are the methods that can have a default implementation. If you have a default method in an interface, it is not mandatory to override (provide body) it in the classes that are already implementing this interface.In short, you can access the default methods of an interface using the objects of the implementing classes.Exampleinterface MyInterface{ public static int num = 100; ...
Read MoreIs it mandatory to use T for type-parameter, while defining Generics classes/methods in Java?
Generics is a concept in Java where you can enable a class, interface and, method, accept all (reference) types as parameters. In other words it is the concept which enables the users to choose the reference type that a method, constructor of a class accepts, dynamically. By defining a class as generic you are making it type-safe i.e. it can act up on any datatype.To define a generic class you need to specify the type parameter you are using in the angle brackets “” after the class name and you can treat this as datatype of the instance variable an ...
Read MoreCan we overload methods of an interface in Java?
Polymorphism is the ability of an object to perform different actions (or, exhibit different behaviors) based on the context.Overloading is one of the mechanisms to achieve polymorphism where a class contains two methods with the same name and different parameters.Whenever you call this method the method body will be bound with the method call based on the parameters.ExampleIn the following Java program, the Calculator class has two methods with name addition the only difference is that one contains 3 parameters and the other contains 2 parameters.Here, we can call the addition method by passing two integers or three integers. Based ...
Read MoreCan we have generic constructors in Java?
Generics is a concept in Java where you can enable a class, interface and, method, accept all (reference) types as parameters. In other words it is the concept which enables the users to choose the reference type that a method, constructor of a class accepts, dynamically. By defining a class as generic you are making it type-safe i.e. it can act up on any datatype.To define a generic class you need to specify the type parameter you are using in the angle brackets “” after the class name and you can treat this as datatype of the instance variable an ...
Read MoreIs it possible to override a Java method of one class in same?
When we have two classes where one extends another and if, these two classes have the same method including parameters and return type (say, sample) the method in the subclass overrides the method in the superclass.i.e. Since it is an inheritance. If we instantiate the subclass a copy of superclass’s members is created in the subclass object and, thus both methods are available to the object of the subclass.But if you call the method (sample), the sampling method of the subclass will be executed overriding the super class’s method.Exampleclass Super{ public static void sample(){ System.out.println("Method of ...
Read MoreHow can we restrict Generics (type parameter) to sub classes of a particular class in Java?
Whenever you want to restrict the type parameter to subtypes of a particular class you can use the bounded type parameter. If you just specify a type (class) as bounded parameter, only sub types of that particular class are accepted by the current generic class.You can declare a bound parameter just by extending the required class with the type-parameter, within the angular braces as −class Sample Examplepublic class BoundsExample { public static void main(String args[]) { Sample obj1 = new Sample(20); obj1.display(); Sample obj2 = new Sample(20.22d); ...
Read MoreWhy subclass doesn't inherit the private instance variables of superclass in Java?
When you declare the instance variables of a class private, you cannot access them in another class if you try to do so a compile-time error will be generated.But, if you inherit a class that has private fields, including all other members of the class the private variables are also inherited and available for the subclass.But, you cannot access them directly, if you do so a compile-time error will be generated.Exampleclass Person{ private String name; public Person(String name){ this.name = name; } public void displayPerson() { System.out.println("Data of the Person ...
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