Can we make a constructor abstract?

Yes, an abstract class can have a constructor in Java. You can either explicitly provide a constructor to the abstract class or if you don't, the compiler will add a default constructor of no argument in the abstract class.

Can we abstract constructor in Java?

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.

How do you call an abstract constructor?

You can't call an abstract class constructor with a class instance creation expression, i.e. As constructors of abstract classes can only be called within subclass constructors (and by chaining one to another within the same class), I typically make them protected ... making them public would serve no purpose.

Can we write constructor in interface?

No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7. From Java8 onwards interfaces allow default methods and static methods.

Can constructor be overloaded?

Constructors can be overloaded in a similar way as function overloading. Overloaded constructors have the same name (name of the class) but the different number of arguments. Depending upon the number and type of arguments passed, the corresponding constructor is called.

Part 8 Can an abstract class have a constructor

Can we make constructor final?

No, a constructor can't be made final. A final method cannot be overridden by any subclasses. As mentioned previously, the final modifier prevents a method from being modified in a subclass. The main intention of making a method final would be that the content of the method should not be changed by any outsider.

Can we create constructor in static class?

A static class can only have static members — you cannot declare instance members (methods, variables, properties, etc.) in a static class. You can have a static constructor in a static class but you cannot have an instance constructor inside a static class.

Can we create immutable class in Java?

Immutable class in java means that once an object is created, we cannot change its content. In Java, all the wrapper classes (like Integer, Boolean, Byte, Short) and String class is immutable. We can create our own immutable class as well.

What is a singleton in Java?

In Java, Singleton is a design pattern that ensures that a class can only have one object. To create a singleton class, a class must implement the following properties: Create a private constructor of the class to restrict object creation outside of the class.

How do you make a class singleton?

What is wrapper object in Java?

A Wrapper class is a class which contains the primitive data types (int, char, short, byte, etc). In other words, wrapper classes provide a way to use primitive data types (int, char, short, byte, etc) as objects. These wrapper classes come under java. util package.

Can constructor be private?

Yes, we can declare a constructor as private. If we declare a constructor as private we are not able to create an object of a class. We can use this private constructor in the Singleton Design Pattern.

Can we override static method?

Overloading is the mechanism of binding the method call with the method body dynamically based on the parameters passed to the method call. Static methods are bonded at compile time using static binding. Therefore, we cannot override static methods in Java.

Can we inherit static class?

Static classes are sealed and therefore cannot be inherited. They cannot inherit from any class except Object. Static classes cannot contain an instance constructor. However, they can contain a static constructor.

Can we overload main method?

Yes, we can overload the main method in Java, but When we execute the class JVM starts execution with public static void main(String[] args) method.

Can constructor be overridden?

Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. But, a constructor cannot be overridden. If you try to write a super class's constructor in the sub class compiler treats it as a method and expects a return type and generates a compile time error.

Can a constructor be synchronized?

Note that constructors cannot be synchronized — using the synchronized keyword with a constructor is a syntax error. Synchronizing constructors doesn't make sense, because only the thread that creates an object should have access to it while it is being constructed.

Can we execute a program without main () method?

Yes, we can execute a java program without a main method by using a static block. Static block in Java is a group of statements that gets executed only once when the class is loaded into the memory by Java ClassLoader, It is also known as a static initialization block.

Can we overload final method?

Can We Override a Final Method? No, the Methods that are declared as final cannot be Overridden or hidden.

Can we inherit static class in Java?

Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables. We can inherit static methods in Java.

Can constructors be virtual?

In C++, the constructor cannot be virtual, because when a constructor of a class is executed there is no virtual table in the memory, means no virtual pointer defined yet. So, the constructor should always be non-virtual. But virtual destructor is possible.

Can a constructor be void?

Note that the constructor name must match the class name, and it cannot have a return type (like void ). Also note that the constructor is called when the object is created.

Can constructor have return type?

No, constructor does not have any return type in Java. Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. Mostly it is used to instantiate the instance variables of a class.

Is overriding possible in Java?

In Java, method overriding occurs when a subclass (child class) has the same method as the parent class. In other words, method overriding occurs when a subclass provides a particular implementation of a method declared by one of its parent classes.

Can we have static constructor in Java?

No, we cannot define a static constructor in Java, If we are trying to define a constructor with the static keyword a compile-time error will occur. In general, static means class level. A constructor will be used to assign initial values for the instance variables.