Checker 框架 - 运行时保留

Question

So I'm trying to use checker framework (from https://checkerframework.org/ ), and I have following code:

import org.checkerframework.checker.index.qual.Positive;

public class Ceker {


  public static void main(String[] args) {
    double a = Double.parseDouble(args[0]);
    System.out.println(new Ceker().preconditions(a));
  }

  public int preconditions(@Positive double a){
    return (int) a;
  }

}

How I uderstood this works, is that I can run something like

javacheck -processor positiveness Ceker.java

and then checker will tell me that I do not have a rule to test if double a is always positive - so I go to main method and change it to:

public static void main(String[] args) {
    double a = Double.parseDouble(args[0]);
    if(a<0){
      throw new IllegalArgumentException("a is not positive!");
    }
    System.out.println(new Ceker().preconditions(a));
  }

Now, my question is - can I just not add that additional checking code, and have that @Positive annotation automatically throw exception at the runtime if contract is violated?

Answer 1

In brief:

• Code behavior modification is outside the scope of the Checker Framework.
• The change you proposed is usually not desirable.
• A run-time check is sometimes impossible.

Here are more details.

1. The Checker Framework is a verification tool that works at compile time. It makes no changes to your code's behavior -- it just tells you whether that behavior might be wrong. You could use a tool that changes your code's behavior in the way you described, but such a tool is different than the Checker Framework.

2. Changing the code to throw an exception is desirable behavior for a public API method, such as main : it gives a user-friendly error message. However, for most methods in your code, the change does no good: it merely changes one exception that crashes your program into a different exception that crashes your program. (It can be a debugging benefit for the exception to be thrown earlier, but that is no consolation to users.) The goal of the Checker Framework is to prevent errors, not to change the way that they manifest.

3. For many type systems, there is no possible run-time test. Section Run-time tests and type refinement in the Checker Framework Manual gives a dozen examples.