Learning Casting in Java

Last updated on August 25, 2020

One of the most renowned programming languages at present is Java. Furthermore, Java application development continues to be a lucrative source of income for many people who are into the tech industry. The language is used to create web platforms and web apps, designed for flexibility, which enables developers to write code that runs on any machine, whatever the platform or architecture may be. Billions of computers and mobile phones throughout the world run Java.

What is Java Casting?

Casting, a process of creating a variable as a variable to another type. Software and app developers are aware of the rapid pace of industry requirements. Nonetheless, some instruments continue to remain significant even in times of regularly fluctuating trends. Undoubtedly, Java is the best choice nowadays for software programmers and developers for many reasons.
With Java casting, if a class shares an IS-A or an inheritance relationship with another interface or class, the variables could be cast to the type of each other. There are times that the cast is permitted and at times not allowed. This is because some of the cast won’t show any error at compilation time but would fail during runtime.

Basic Rules When Casting Variables

  • Casting an object from a superclass to a subclass needs an explicit cast
  • Casting an object from a subclass to a superclass
  • The compiler does not allow casts to unrelated types

Understanding Java Casting

The popularity of Java application development has been responsible for the surge in the demand for Java tutorials. Amid the many topics, Java casting remains one of the most puzzling concepts in the language, even if it’s one of the easiest to comprehend.

Basic Java Casting Rules

First and foremost there should be a definition of the term. The process of casting is to take an object of a particular kind and transform it into another. This is just one of the vital reasons that casting and conversion is an analogous process of Java. It’s important to note that casting is not Java-specific since most other languages support it as well. Nevertheless, the language has specific variables casting restrictions to not cast any variable to a random kind. It, therefore, needs Java casting rules to focus to comprehend the best ways. The Java SE 11 release also has come up with several new features “regarding casting”.

Casting Primitives

One of the main issues related to casting directly points to the two groups in Java, the primitive and reference. Primitives refer to double, int, long, float and other types of data. References on the other hand, includes type classes, interfaces or arrays. Nonetheless, one of the critical points related to casting refers to explicit and implicit changes. In some instances, the system could change the type of expression itself, based on specific requirements. Check out this example:


Int num1 = 5;
Double num2;
Double a = num1/num2;

In the last code line, automatic typecasting of num1 turns to ‘double’ automatically. The next major concern comes with explicit casting or Java typecasting. Developers should specify what type an object should be cast, in case changes don’t happen automatically. The following is the basic syntax for type casting:

Identifer2= (type) identifer1;

For instance,

num1=(int) num2;

Combined widening and narrowing primitive conversion

Developing an overall understanding of Java casting becomes easier. The widening or upscale of primitive types inclusion is converting from a smaller primitive into a bigger one. In primitives widening, the smaller value assumes a bigger container, which leaves plenty of space. So, the space located on the left is filled with zeros. Moreover, one cannot move towards a floating-point from the integer group. Check this out:

Int myint = 12; 
long myLong = myint; 
float myFloat = myLong; 
double myDouble = myLong;

Another form of casting is narrowing primitives wherein you fit a larger value than the specified type in a variable declaration, thus information loss is imperative because of discarding some bytes. Furthermore, narrowing primitives demand explicit expression regarding cast usage and provide a basic idea about Java downcasting. Understand it better with the following example:

Int myint = (int) myDouble;
byte myByte = (byte) myint;

Upcasting,Downcasting

Upcasting includes supertype casting. Downscaling, on the other hand, means casting to a subtype. Both help provide advantages, including a facility for grouping of different objects or polymorphism. Upcasting means widening or generalization through casting to a parent type.

Object Casting

  • Objects of the same class could be assigned with one another.
  • Subclass object may be assigned to a super class object. This is done implicitly and known as upcasting, which means upwards in the hierarchy, from subclass to superclass.
  • Java doesn't allow assigning a superclass object to a subclass one. To do so would require explicit casting, or known as downcasting. This required explicit conversion.

It's possible here to pass an instance of any class for ‘object’ argument, which includes all Java classes in the ‘object’ subclasses. In the case of ‘component’ argument, it’s possible to pass it in subclasses such as label, button and container in ‘java.awt’. Object casting is applicable also anywhere in a program, not just for method calls. Variables with a class ‘component’ definition allows assigning objects of the class or subclasses to object without the need for casting. The contrast is also applicable since a superclass could be used in places wherein a subclass is expected. Because subclasses have more behavior than superclasses, a significant precision loss is clear with the process of casting.

Reference Casting

Casting and conversion of reference types also is a prominent topic for casting evaluation. References involve a range of interface and type class. There are two specific methods for casting, namely, assignment conversion and method invocation. Conversion assignment has the inclusion of assigning reference type to a value of different kinds. Object reference conversion follows certain rules that apply to Java casting. The interface type conversion is only possible to an object or interface type. In casting to a new type of interface, the new interface should be superior compared to the old one.

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About Joanna Baretto

Joanna Baretto is a Business Analyst at tatvasoft.com.au, which is a leading java application development company, She has been working for four years in the tech domain. Her work across multiple disciplines broadly addresses the narratives of techno experience. You can find her on Twitter @BarettoJoanna.

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