FAQ: How To Downcast In Java?

Can we downcast in Java?

Upcasting is allowed in Java, however downcasting gives a compile error. The compile error can be removed by adding a cast but would anyway break at the runtime.

What do you mean by Upcasting in Java?

Upcasting is the typecasting of a child object to a parent object. Upcasting can be done implicitly. Upcasting gives us the flexibility to access the parent class members but it is not possible to access all the child class members using this feature.

What is the purpose of downcasting in Java?

Use downcasting when we want to access specific behaviors of a subtype. Here, in the teach() method, we check if there is an instance of a Dog object passed in, downcast it to the Dog type and invoke its specific method, bark().

What is the use of Upcasting and downcasting in Java?

Up-casting is casting to a supertype, while downcasting is casting to a subtype. Upcasting and downcasting gives us advantages, like Polymorphism or grouping of different objects. We can treat an object of a child class type to be as an object of its parent class type. This is called upcasting.

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Why is string immutable in Java?

The String is immutable in Java because of the security, synchronization and concurrency, caching, and class loading. The reason of making string final is to destroy the immutability and to not allow others to extend it. The String objects are cached in the String pool, and it makes the String immutable.

What is overriding in Java?

In any object-oriented programming language, Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes.

How do I convert one type to another in Java?

When you assign value of one data type to another, the two types might not be compatible with each other. If the data types are compatible, then Java will perform the conversion automatically known as Automatic Type Conversion and if not then they need to be casted or converted explicitly.

Is Upcasting safe?

Upcasting is safe and it does not fail. We need to check the instance of the object when we downcast the object using instanceof operator or we might get ClassCastException.

What is serialization in Java?

To serialize an object means to convert its state to a byte stream so that the byte stream can be reverted back into a copy of the object. A Java object is serializable if its class or any of its superclasses implements either the java. Serializable interface or its subinterface, java. io.

Why is downcast needed?

Here, you were forced to downcast, because you haven’t defined the method in the super class. As compiler cannot see the definition of that method in Student class. It has no idea about what the actual object s1 points to. Remember, compiler only checks the reference type to find the meethod declaration.

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Can we override static method?

Static methods cannot be overridden because they are not dispatched on the object instance at runtime. The compiler decides which method gets called. Static methods can be overloaded (meaning that you can have the same method name for several methods as long as they have different parameter types).

What is the use of final keyword in Java?

Java final keyword is a non-access specifier that is used to restrict a class, variable, and method. If we initialize a variable with the final keyword, then we cannot modify its value. If we declare a method as final, then it cannot be overridden by any subclasses.

Is a relationship in java?

In Java, an Is- A relationship depends on inheritance. Further inheritance is of two types, class inheritance and interface inheritance. When there is an extends or implement keyword in the class declaration in Java, then the specific class is said to be following the Is-A relationship.

What is Polymorphism in java?

Polymorphism in Java is the ability of an object to take many forms. To simply put, polymorphism in java allows us to perform the same action in many different ways. In the technical world, polymorphism in java allows one to do multiple implementations by defining one interface.

What is Instanceof in java?

The java “instanceof” operator is used to test whether the object is an instance of the specified type (class or subclass or interface). It is also known as type comparison operator because it compares the instance with type. It returns either true or false.

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