Is there any way to predefine length of an array parameter by annotations

问题

I'm working on a sudoku solving application and i dont want to write a code such as

Method(int[] i)
{
   if(i.length == 9)
      {
      // do stuff
      }
   else
      {
      // throw...
      }
}

is there any way to enforce arrays parameter to be exact 9 integer by using annotations such as

Method(@SizeNine int[] i)
    {
       //do stuff
    }

回答1:

Yes, this is possible, using a compiler plugin.

Use the @ArrayLen annotation to declare a method whose argument must be a length-9 array of Strings:

void myMethod(String @ArrayLen(9) [] a) {
  ...
}

Then, compile your program using the Index Checker of the Checker Framework:

javac -processor index MyJavaFile.java

Now, javac will issue a compile-time warning if any client tries to pass an array whose length is not guaranteed to be 9. If there is a warning, you can fix it and re-compile. There is no need to perform a run-time check of the array length within your implementation.

回答2:

You can't enforce it on an array (length is not part of the array type in Java, unlike some other languages).

However, you can define a class like this:

final class IntArrayWithLength9 {  // Obv you can use a better name.
  private final int[] arr = new int[9];

  void set(int i, int value) { arr[i] = value; }
  int get(int i) { return arr[i]; }
}

Now, you know that if you've got an instance of this class, then the array has length 9, thus you don't need to check it.

So, you can now use IntArrayWithLength9 instead of int[].

来源：https://stackoverflow.com/questions/50122408/is-there-any-way-to-predefine-length-of-an-array-parameter-by-annotations

标签

java

arrays

annotations