Java 22: Unnamed Variables and Patterns

Java 22 introduces Unnamed Variables & Patterns. Unnamed variables are placeholders denoted by the underscore character (_) that stand in for variable names, particularly in situations where the variable's identifier is insignificant or redundant. They can be declared in several contexts, including local variable declarations, catch clauses, lambda expressions, and more. By omitting explicit variable names in scenarios where the variable name serves no functional purpose, code becomes more succinct, reducing unnecessary verbosity and aiding readability.

Here are a few examples of unnamed variables in action:

For-loop:

for (Order _ : orders) {
  doSomething();
}

Assignment statement:

Queue<Integer> q = ... // x1, y1, z1, x2, y2, z2, ...
var x = q.remove();
var y = q.remove();
var _ = q.remove();

Lambda expressions:

list.stream().mapToInt(_ -> 1).sum();

Exception handling:

String s = ...
try {
  int i = Integer.parseInt(s);
} catch (NumberFormatException _) {
  System.out.println("Invalid number: " + s);
}

Try-with-resources:

try (BufferedReader _ = new BufferedReader(...)) {
  System.out.println("File opened successfully.");
} catch (IOException _) {
  System.err.println("An error occurred while opening the file.");
}

Unnamed pattern variables:

switch (shape) {
  case Circle _ -> process(shape, 0);
  case Triangle _ -> process(shape, 3);
  case Rectangle _ -> process(shape, 4);
  case var _ -> System.out.println("Unknown shape");
}

Unnamed Patterns

Unnamed Patterns provide an elegant solution when you need to match a pattern without extracting specific components. If you have nested data structures, such as records within records, with unnamed patterns, you can focus on extracting the necessary components without cluttering your code with unnecessary variable assignments.

record Address(String city, String country) {}
record Person(String name, int age, Address address) {}

if (person instanceof Person(var name, _, Address(var city, _))) {
  System.out.println(name + " lives in " + city);
}

So, the next time you encounter a situation where the variable name seems inconsequential, consider using an unnamed variable to streamline your code.