Introduction
Did you know that Java is one of the easiest programming languages and can still land you a high-paying job?
In India, a Java developer’s salary is in the range of Rs. 2 Lakhs- Rs. 11 Lakhs. However, your dream of becoming one can turn into a reality only when you have a strong foundation in technical concepts.
Read this article to gain an in-depth understanding of variables in Java, their types, and their importance in writing clean code.
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What is a Variable in Java?
A variable in Java is a container for storing data, which can be manipulated while executing a program. For the successful storage and manipulation of different data types, variables need to have their specific data types.
The two main data types in Java are: Object or Reference data types and Primitive data types. Once the data types are assigned to the variables, they are ready for storing characters, integers, or decimals.
Also Read: Java Interview Questions With Real-Time Coding Examples
Types of Variables in Java
There are primarily three main types of Java variables, each having its own use cases and suitability for particular types of data. These include:
Local Variables
These variables are used and declared inside a particular block of code, constructors, or methods.
Creation and Discarding: They are created upon entering the block, method, or constructor, and discarded after their exit.
Default Value: Local variables do not have a default value. They must be explicitly initialised before use.
Class or Static Variables
These variables are declared in a class using a ‘static’ keyword. However, this is done outside a code, a constructor, or a method.
Creation and Discarding: They are created once the program starts, and are discarded as soon as the program stops.
Default Value: They have the same default values as instance variables.
Instance Variables
These variables are also declared within a class and outside a constructor, code, or method.
Creation and Discarding: They are created at the time of object creation using the ‘new’ keyword, and discarded with the object’s destruction.
Default Value: They have default values as follows:
- For numbers: 0.
- For booleans: false.
- For object references: null.
Java Variable Declaration: Its Meaning, Rules, and Uses
In Java, variable declaration means specifying the data type, giving the variable a name, and optionally assigning an initial value. This tells the compiler about the variable’s existence, type, and scope.
Its Rules
There are several rules followed in the declaration of variables in Java. A few important ones include:
- Variable names may contain letters, both upper case and lower case; the digits 0-9; the underscore (_) sign, and/or the dollar ($) sign.
- Variable names must not have blank spaces.
- Avoid beginning variable names with an upper-case letter or a digit.
- The variable names must not be any of the Java keywords.
- They are case-sensitive.
- Though there is no hard and fast rule regarding the character limit of variable names, maintain a character length of 4-15.
Uses
Variable declaration has many important uses in Java programming. These include:
- Memory Allocation: After variable declaration, the allocation of suitable memory space for storing the variable’s value, depending on the data type, is done by the Java Virtual Machine (JVM).
- Specifying the Data Type: As a variable declaration defines the data type which a variable can store, it is helpful for the compiler in conducting type checking, preventing incompatible data assignments, and catching errors early.
- Prevention of Error: Using undeclared variables leads to compile-time errors, ensuring that all variables are compulsorily declared to avoid issues related to undefined references.
- Creation of Clean Code: Variable declaration using meaningful names significantly enhances the code’s readability. This helps in improving the clarity of the variable’s purpose, allowing you to maintain and debug large applications.
- Defining the Variable’s Scope: By knowing the variable’s scope after variable declaration, you can understand where to access and modify it in the program.
- Variable Initialisation: Assigning an initial value during declaration gives the variable a defined state before use in computations.
Also Read: Constructor Overloading in Java: Essential Skill for Developers
Instanceof Java Keyword: Meaning and When to Avoid It?
In Java, the ‘instanceof’ is a keyword that helps check if an object is a particular interface or class. Though this keyword is helpful in some ways, it is generally advised to be avoided unless necessary. It should be avoided in the following scenarios:
- Tight Coupling and Difficult Maintenance: A heavy use of the ‘instanceof’ keyword often results in tightly coupled code. This results in changes to the class hierarchy requiring modifications in many places where type checks are done.
- Where Polymorphism Can Be Done: The ‘instanceof’ keyword lacks polymorphism, which makes the code too wordy. As a polymorphic code relies on the object’s behaviour rather than its type, it is simpler and easier to follow.
- Code Smell: The use of ‘instanceof’ is often considered a ‘code smell’ as it goes against the principles of OOP (Object Oriented Programming), particularly polymorphism.
- When Design Flaws are Indicated: Extensively using ‘instanceof’ can indicate that your class design may not be utilising inheritance and interfaces effectively. This again emphasises the need to use polymorphism.
Mistakes to Avoid While Using Variables in Java
While Java variables have a wide variety of uses in programming, there are certain common mistakes that developers should avoid. These include:
- Not Initialising Local Variables: Initialisation of local variables is non-negotiable to avoid compile-time errors, as Java does not allow the usage of uninitialised ones.
- Using Incorrect Variable Names: The naming of Java variables must be done in accordance with its conventions to ensure they are readable and easy to maintain.
- Misunderstanding Variable Scope: Understanding variable scope is important to ensure that you are not trying to access a variable outside its defined scope, as doing so will lead to an error.
- Not Using the ‘final’ Variable for Constants: The use of a ‘final’ variable for constants makes the code easier to modify and reduces errors.
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Conclusion
From the correct way to define variables in Java and variable declaration to understanding the mistakes to avoid while handling them, you are now equipped with the knowledge necessary for writing effective code using variables. As a Java developer, understanding this concept is mandatory for success in this field.
To expand your knowledge further, consider pursuing the online programmes at Amity University Online to seek guidance from world-class faculty and gain access to top-notch online resources.
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