Description Noopur Gupta 2017-05-09 11:42:38 EDT

package p;

public class Test {
	public static void main(String[] args) {
		for (int i = 0; i < 1; i++) {
			int idx = 0;
			for (int j = 0; j < 3; j++) {
				idx++;
				System.out.println(idx);
			}
			// for-loop to extract:
			for (int j = 0; j < 3; j++) {
				idx++;
				System.out.println(idx);
			}
		}
	}
}

Extracting the second for loop does not consider the first for loop as a valid duplicate as the first loop should return an 'int' whereas the second for loop returns 'void'.

This can be improved by creating an extracted method that returns 'int':

public class Test {
	public static void main(String[] args) {
		for (int i = 0; i < 1; i++) {
			int idx = 0;
			idx = extracted(idx);
			idx = extracted(idx);
		}
	}

	private static int extracted(int idx) {
		for (int j = 0; j < 3; j++) {
			idx++;
			System.out.println(idx);
		}
		return idx;
	}
}

See bug 479559 comment #9:
> For the example in comment 0, it would actually be nice to have the
> refactoring find the duplicate code. If you add another
> System.out.println(idx); after to for-loop to extract, or if you extract the
> first for-loop, the refactoring already works fine and uses the return value
> of the extracted method to update the idx variable. a() and b() in the
> snippet from comment 6 are the same case.
> 
> Implementing that is a bit trickier and should probably left as a separate
> enhancement request: In case the extracted snippet returns void but a
> structural duplicate returns a value, we could create an extracted method
> that returns that value. That would also mean the return type of the
> extracted method would have to change depending on whether duplicates should
> be extracted or not. 

It should also consider the case where multiple duplicates are present and have different return values. See bug 479559 comment #6 attachment 265525 [details] for example. In this case, we can either extract only the selected snippet returning 'void' without any duplicates (the current behavior) or, choose a return value (random or one being returned the max no. of times) from the duplicate snippets to create the extracted method.