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Java var Keyword - var is not keyword

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Java's "var" Keyword – Making Code Shorter and Life Easier (and Funnier!)​

Java has been on a mission to reduce verbosity in its syntax, like a chef trimming unnecessary ingredients for a perfect dish. First, it introduced the Diamond operator <>, and now, it has given us var (JEP 286) to declare variables.

So, what's the deal with var? Well, instead of writing long-winded type declarations, the compiler does the heavy lifting and infers the type for you. Think of it as Java going, "Relax, I got this!" 🚀

The Magic of var​

Consider this example:

var str = "Hello world";

This is Java being smart and automatically understanding that str is of type String. Essentially, the above line is equivalent to:

String str = "Hello world";

1. Declare and Initialize – A Must​

Java is quite strict about var. You must initialize the variable right when you declare it. Otherwise, Java throws a tantrum (a.k.a a compilation error). 😱

❌ Bad:

var i; // ERROR: Cannot use 'var' on variable without initializer

✅ Good:

var j = 10; // Works like a charm!

2. var is NOT a Keyword! (Surprise! 🎉)​

Even though var looks like a keyword, it isn’t. This means you can have a variable named var. Java won't stop you (but your teammates might). 🙈

var var = 10; // Java: "Sure, why not?"
int var = 10; // Still valid!

But just because you can doesn’t mean you should! (Please, think of future developers!)

3. Where Can You Use var? 🤔​

Java is picky about where var can be used. It works in:

  • Local variables with initializers
  • Indexes in enhanced for-loops
  • Loop variables in traditional for-loops

✅ Allowed​

var blogName = "howtodoinjava.com"; // Local variable with initializer

for (var object : dataList) { // Enhanced for-loop index
    System.out.println(object);
}

for (var i = 0; i < dataList.size(); i++) { // Traditional for-loop variable
    System.out.println(dataList.get(i));
}

❌ Not Allowed​

Java says NO! to var in these cases:

  • Method parameters
  • Constructor parameters
  • Method return types
  • Class fields
  • Catch block parameters
public class Application {
    // var firstName; ❌ Not allowed as class fields
    
    // public Application(var param) { } ❌ Not allowed as constructor parameter
    
    // try { } catch (var ex) { } ❌ Not allowed in catch blocks
    
    // public var demoMethod() { return null; } ❌ Not allowed in return types
    
    // public Integer demoMethod2(var input) { return null; } ❌ Not allowed in method parameters
}

4. Performance? No Worries! 😎​

Since Java determines the type at compile time, the resulting bytecode is identical to explicitly declared types. This means no extra runtime processing, no extra memory usage, and no performance impact. In short: Java is still lightning fast! ⚡

5. Conclusion 🎯​

Using var can make code concise and easier to read, especially when dealing with complex generics. But don’t overdo it—too much var and your code might start looking like an unsolvable puzzle. 🧩

Use it wisely, and Java will love you back! ❤️

Happy Coding! 🚀