对于每个不执行的循环

Question

For some reason all the for-each loops in my method are completely ignored, and I cannot figure out why. Here is my code:

private static boolean notUsed(ArrayList<Integer> check, ArrayList<ArrayList<Integer>> used)
  {
    boolean c1 = false;
    boolean c2 = true;
    for (ArrayList<Integer> item : used) // Not executed
    {
      System.out.println("It works!");
      Collections.sort(item);
      Collections.sort(check);
      if (check.equals(item)) c1 = true;
    }
    ArrayList<Integer> existing = new ArrayList<Integer>();
    for (int item : check)
    {
      for (int exists : existing) // Not executed
      {
        if (exists == item) 
        {
          c2 = false;
          break;
        }
        else existing.add(item);
      }
      if (c2 == false) break;
    }
    if (c1 && c2) return true;
    else return false;
  }

I have been going over it for the past 15 minutes and fail to see why the code refuses to bother with the contents of the loops. In fact, I didn't even know java could avoid executing loops before now. Am I missing something obvious?

Answer 1

Yes, you are missing something obvious.

If those loops aren't executing, then there are no elements in the arguments passed to the routine.

Answer 2

You make a new ArrayList

ArrayList<Integer> existing = new ArrayList<Integer>();

which is empty.

When the foreach runs, it has nothing to iterate over. Therefore, your "not executing" comment is perfectly valid.

The first loop however, depends on what exactly is passed. Put some print statemtents figure out the size of the List. Most likely, that is 0 as well, which again, causes the loop to be "skipped".

Answer 3

的大小used必须在0和第二环路不执行，因为existing是一个新的ArrayList和其大小绝对是0

Answer 4

here is working code..this will give you idea. As others mentioned..there would not be any elements to iterate...because i ran the below code and for each loop works...

import java.util.ArrayList;
import java.util.Collections;


public class Test1 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        ArrayList<ArrayList<Integer>> used = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer>item = new ArrayList<Integer>();
        item.add(1);
        used.add(item);
        notUsed(item,used );
    }

    private static boolean notUsed(ArrayList<Integer> check, ArrayList<ArrayList<Integer>> used)
      {
        boolean c1 = false;
        boolean c2 = true;
        for (ArrayList<Integer> item : used) // Not executed
        {
          System.out.println("It works!");
          Collections.sort(item);
          Collections.sort(check);
          if (check.equals(item)) c1 = true;
        }
        ArrayList<Integer> existing = new ArrayList<Integer>();
        for (int item : check)
        {
          for (int exists : existing) // Not executed
          {
            if (exists == item) 
            {
              c2 = false;
              break;
            }
            else existing.add(item);
          }
          if (c2 == false) break;
        }
        if (c1 && c2) return true;
        else return false;
      }

}