Final variable assignment with try/catch

Question

Because I believe it is a good programming practice, I make all my (local or instance) variables final if they are intended to be written only once.

However, I notice that when a variable assignment can throw an exception you cannot make said variable final:

final int x; try {     x = Integer.parseInt("someinput"); } catch(NumberFormatException e) {     x = 42;  // Compiler error: The final local variable x may already have been assigned } 

Is there a way to do this without resorting to a temporary variable? (or is this not the right place for a final modifier?)

Answer 1

One way to do this is by introducing a (non-final) temporary variable, but you said you didn't want to do that.

Another way is to move both branches of the code into a function:

final int x = getValue();  private int getValue() {   try {     return Integer.parseInt("someinput");   }   catch(NumberFormatException e) {     return 42;   } } 

Whether or not this is practical depends on the exact use case.

All in all, as long as x is a an appropriately-scoped local variable, the most practical general approach might be to leave it non-final.

If, on the other hand, x is a member variable, my advice would be to use a non-final temporary during initialization:

public class C {   private final int x;   public C() {     int x_val;     try {       x_val = Integer.parseInt("someinput");     }     catch(NumberFormatException e) {       x_val = 42;     }     this.x = x_val;   } }