Looping in ArrayLists with a Method

问题

With much assistance I have developed a method that makes anagrams and then adds them into an ArrayList.

public void f(String s, String anagram, ArrayList<String> array)
{
    if(s.length() == 0)
    {
        array.add(anagram);
        return;
    }
    for(int i = 0 ; i < s.length() ; i++)
    {
        char l = s.charAt(i);
        anagram = anagram + l;
        s = s.substring(0, i) + s.substring(i+l, s.length());
        f(s,anagram,array);
    }
}

The problem is when I attempt to use this function to make ArrayLists in a loop that adds Strings from one ArrayList to another, I get an error saying I can't use a void, and the method f() is void.

        List<String> Lists = new ArrayList<String>(); //makes new array list
        for(String List : words)
        { //takes values from old array list
            List.trim();
            Lists.add(f(List,"",new ArrayList<String>())); //this is where it doesn't work
        }

Let me clarify once more: I want to use this function to insert ArrayLists of anagrams into each position in another ArrayList. The anagram Lists are derived from Strings that are being read from one list to another. I tried changing the method to static but that doesn't work, I also removed the return; in the method once, but that doesn't fix it either.

How do I make this whole thing work?

回答1:

The error happens because the method f() is void, meaning: it doesn't return any value that can be added to the ArrayList.

The answer of invoking f() is stored in the ArrayList passed as a parameter to f, you should probably use that ArrayList to add all of its elements to Lists. Something like this:

List<String> lists = new ArrayList<String>();
for (String list : words) {
    list.trim();
    ArrayList<String> answer = new ArrayList<String>();
    f(list, "", answer);
    lists.addAll(answer);
}

回答2:

Your method header for F needs to look like this:

public String f(String s, String anagram, ArrayList<String> array)

And then you return a String value to add to that ArrayList you are using.

回答3:

Your function definition for f() shows the return value of type void. So looking at your code you're attempting to do this:

Lists.add(void);

which is obviously illegal.

Your choice really is to have the ArrayList declared in a greater scope.

private List<String> anagrams;

public void f(String s, String anagram) {
  ...
  anagrams.add(anagram);
  ...
}

....

 for(String List : words) {
   //takes values from old array list
   anagrams = new ArrayList<String>();
   List.trim();
   f(list,"");
   Lists.add(anagrams); //this is where it doesn't work
 }

来源：https://stackoverflow.com/questions/15396858/looping-in-arraylists-with-a-method

标签

java

methods

multidimensional-array

arraylist

anagram