Java doesn’t support truly dynamic variable names like scripting languages do, but similar behavior can be achieved using HashMap or List structures. A HashMap <String, Object> allows you to store values with dynamic keys, acting like variable names. By using arrays or lists, you can store values dynamically and access them by the help of their indices.
In this article, you’ll learn why Java doesn’t support dynamic variable names and how to achieve similar functionality in a simple and effective way.
Table of Contents:
What are Dynamic Variables in Java?
Java is statically typed, so variable types are determined at compile time. However, using the Object class or polymorphism, you can store and interact with different data types at runtime.
However, Java does not support true dynamic typing like some other languages (e.g., Python or JavaScript). In Java, the type of a variable is always declared and fixed at compile time.
Example:
Output:
Explanation: In the above code, the dynamicVariable is defined as the type Object. Further, it is used as a different data type, i.e., integer, string, and float.
Why Java Doesn’t Allow Dynamic Variable Names?
Java does not support dynamic variable names because it is a statically typed language, i.e., all the variable names and their types present in the code should be known at compile time. Due to this, the Java compiler does the type checking and then generates the bytecode. If dynamic variable names were allowed, the Java compiler would not be able to ensure this type checking of the program.
While JVM memory allocation is managed automatically, Java doesn’t allow creating variable names dynamically at runtime, as this would violate its static typing model. Hence, the variables that would be created dynamically could lead to runtime errors. Instead of dynamic variables, Java has a Map or a HashMap, which can be used by the user to keep
Things are clear, safe, and easy to manage.
Polymorphism and Dynamic variables
Polymorphism enhances the dynamic variables as it allows them to perform operations in multiple object types by the same superclass or interface. In Java, an Object type variable can store different types of data dynamically; However, it also requires the need of type casting for some operations. By using inheritance, a superclass object can hold subclass objects, which enables method overriding for dynamic behavior at runtime. Similarly, interfaces allow a single dynamic variable to reference multiple implementing classes, which promotes loose coupling as well as flexibility. The ability to dynamically change this behavior at runtime makes polymorphism a key principle in writing scalable and maintainable Java applications.
Polymorphism allows the dynamic variables to take different forms. These are as follows
1. Using an Object as a Dynamic Variable
Since Object is the superclass of all Java classes, it can store different data types dynamically.
Example:
Object dynamicVar;
dynamicVar = "Hello"; // String
dynamicVar = 42; // Integer (Autoboxing)
dynamicVar = 3.14; // Double
2. Polymorphism with Inheritance
A reference to a superclass can hold the objects of its subclasses, which enables method overriding.
Example:
In the above Java code, the class Dog inherits from Animal using the extends keyword. The makeSound() method is overridden in the class Dog, and due to dynamic dispatch, the Dog is called at runtime.
Output:
3. Polymorphism with Interfaces
The reference of an interface can hold the objects of multiple classes, which ensures flexibility.
Example:
Output:
Explanation: In the above Java code, a Vehicle interface reference holds a Car object, and the start() method is implemented in Car and called at runtime.
Dynamic Variables by Using Collections and Methods
The dynamic variables in Java can be implemented by using different collections, like ArrayList, HashMap, etc.
1. Using the ArrayList()
ArrayList is a dynamic collection of variables that can store variables of a specific type dynamically, as per the user. Its size can be changed dynamically as per the requirements of the user.
Example:
Example:
Output:
Explanation: In the above code, a single ArrayList, which is made up of the type Object, is storing the different types of variables, i.e., integer as 42, string as Intellipaat, and float as 3.14.
2. Using the HashMap()
HashMap is a type of object that can store different types of variables and also allow the dynamic retrieval of them.
Example:
Output:
Explanation: In the above code, the hash map keys are made up of Strings, and the values are defined as objects, which ensures that it can hold the values in different data forms.
3. Using the Methods
Dynamic variables can be useful when using the data type of the method as Object, as they can store different types of data.
Example:
Output:
Explanation: In the above code, the argument of the method is defined as the object type, which allows it to read any values in any data type, i.e., string, integer, float, and boolean.
Drawbacks of Dynamic Variables in Java
1. Lack of Type Safety
As it is checked at runtime, the dynamic variables use the Object as the type definition, it can lead to runtime errors due to incorrect type casting.
Example:
Object num = "Hello";
int value = (int) num; // ClassCastException at runtime
The above code will give the error message as “Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer”
2. Performance Overhead
Sometimes, the object type is explicitly type casted, which can lead to more processing of the program as well as the storage.
Example:
Object obj = 100;
int num = (int) obj; // Object → Integer → int
3. Harder Code Maintenance & Debugging
Dynamic variables hide the actual data type of the method or Collections, which makes them harder to understand for the user. Debugging also becomes more complex due to different data types.
Conclusion
Dynamic variables in Java help us to store different types of values by using Object, HashMap, and ArrayList. They make handling the data easier and support polymorphism. However, they can cause errors and slow down the performance.
To know more about this topic, you can refer to our Java Course.
Assigning variables with dynamic names in Java - FAQs
Q1. Does Java have dynamic variables?
No, Java does not directly support the use of dynamic variables. It can be done by the use of Collections.
Q2. What is dynamic memory allocation in Java?
Dynamic memory allocation is a mechanism by which programs can obtain memory at runtime.
Q3. How to pass a method name dynamically in Java?
You can call a method by name by using the Class.
Q4. Where does Java store variables?
Stack memory is a memory structure used for storing local variables and function calls in a Java program.
Q5. What is the super keyword in Java?
The super keyword refers to superclass (parent) objects.