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Nov 2, 2022 · A constructor is used to initialize an object not to build the object. As we all know abstract classes also do have a constructor. So if we do not define any constructor inside the abstract class then JVM (Java Virtual Machine) will give a default constructor to the abstract class.
Nov 4, 2008 · Yes, an abstract class can have a constructor. Consider this: abstract class Product { . int multiplyBy; public Product( int multiplyBy ) { this.multiplyBy = multiplyBy; } public int mutiply(int val) { return multiplyBy * val; } } class TimesTwo extends Product { public TimesTwo() { super(2); } } class TimesWhat extends Product {
Abstract classes can have constructors, but they cannot be instantiated directly. The constructors are used when a concrete subclass is created. There may be one or greater abstract methods in an abstract class, which signifies that those methods are not implemented by means of the class.
People also ask
Can abstract classes have constructors?
What if an abstract class extends another class without a default constructor?
How to declare a constructor with no arguments in abstract class?
What is an abstract class?
- Overview
- Default Constructor
- No-arguments Constructor
- Parametrized Constructors
- Conclusion
Abstract classes and constructors may not seem to be compatible. A constructor is a method called when a class is instantiated, and an abstract class cannot be instantiated. It sounds counterintuitive, right? In this article, we’ll see why abstract classes can have constructors and how using them provides benefits in subclasses instantiation.
When a class doesn’t declare any constructor, the compiler creates a default constructor for us. This is also true for abstract classes. Even when there’s no explicit constructor, the abstract class will have a default constructor available. In an abstract class, its descendants can invoke the abstract default constructor using super():
We can declare a constructor with no arguments in an abstract class. It will override the default constructor, and any subclass creation will call it first in the construction chain. Let’s verify this behavior with two subclasses of an abstract class: Let’s see the output we get when callingnew ConcreateClassA(): While the output for calling new Co...
One of the most common uses for constructors in abstract classes is to avoid redundancy. Let’s create an example using cars to see how we can take advantage of parametrized constructors. We begin with an abstract Car class to represent all types of cars. We also need a distanceproperty to know how much it has traveled: Our superclass looks good, bu...
Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses. In this article, we went through each type of constructor from the perspective of abstract classes – how they’re related to concreate subclasses and how can we use them in practical use cases. As always, code samples...
Sep 26, 2023 · An instance of an abstract class can not be created. Constructors are allowed. We can have an abstract class without any abstract method.
Aug 29, 2021 · The main purpose of the constructor is to initialize the newly created object. In abstract class, we have an instance variable, abstract methods, and non-abstract methods. We need to initialize the non-abstract methods and instance variables, therefore abstract classes have a constructor.
Mar 11, 2022 · By creating an abstract class that has a constructor, you ensure that its subclasses will have the final variable initialized. The variable is initialized when an instance of the subclass is created and then can’t be changed.
