JAVA fill a temporary Arraylist with objects and then add it into a ArrayList which consists of arrayLists

Question

I iterate through an Array which consists of objects. I want to find certain parts of this array in which the same specific objects follow eachother.

[a,b,c,#,#,#,h,g,a,#,#,s,#.h] --> I want to find #,#,# and #,# (# is the specific object)

I already figured out how to do this: If I find a '#' I will add this object to a temporary ArrayList. If the next object is a '#' too, I will add it aswell, otherwise I clear the tmplist, because it is a single '#'. If the next object is not a # but the tmplist is bigger than 1 i want to add the tmplist to a 2d ArrayList (An ArrayList which consists of ArrayLists) and clear the tmplist so I can find other parts.

Here is my problem: If i do this the the 2d arraylist does not consist of deepcopys of the templists--> The 2d arraylist consist of empty lists, because I clear the tmplist after every found "pattern". How can I fix this?

Some code which might explain it better:

List<Object> tmplist = new ArrayList<Object>();
   for (int i = 0; i<array.length(); i++) {
       if (array[i].equals(#)) {
          tmplist.add(array[i]);
              if (!array[i+1].equals(#) && tmplist.size() < 2){
                  tmplist.clear();
              } else if (!array[i+1].equals(#) && tmplist.size() > 1) {
                   pattern.add(tmplist);
                   tmplist.clear();
              } 
       }
   }
   //pattern is the 2d ArrayList (ArrayList which consists of ArrayLists)

http://stackoverflow.com/questions/1564832/how-do-i-do-a-deep-copy-of-a-2d-array-in-java — blueygh2, Jul 22 '15 at 19:06
If you ever encounter a `[a,b,c,#,#,#]`. Your code is bound to explode with an `IndexOutOfBoundsException`! — Jason Sparc, Jul 22 '15 at 19:27

score 4 · Accepted Answer · answered Jul 22 '15 at 19:08

4

if your 2d ArrayList is : result

do

 result.add(new ArrayList<>(tmpList));

By doing this, you are not adding the tmpList itself but a new list with the values of tmpList. So even If you do tmpList.clear() it will not affect the arraylist in your result.

answered Jul 22 '15 at 19:08

Karthik

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1

@Peter111 I am glad that it helped :) – Karthik Jul 22 '15 at 19:28

score 2 · Answer 2 · answered Jul 22 '15 at 19:06

2

Instead of doing tmplist.clear() do tmplist = new ArrayList<>() so you're working with a different List instance each time.

answered Jul 22 '15 at 19:06

heenenee

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score 1 · Answer 3 · answered Jul 22 '15 at 19:08

1

I think easiest solution would be to not clear the list, but instead assign to tmplist new reference to ArrayList, after adding it to list of lists.

answered Jul 22 '15 at 19:08

newfolder

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score 1 · Answer 4 · answered Jul 22 '15 at 19:20

Ok..I know you must have sorted this out by now using the suggestions.... but I just thought I would make program to do this ... Here is what my solution looks like, not the best way to do it perhaps, but should work ...

import java.util.ArrayList;


import javax.swing.text.rtf.RTFEditorKit;

public class ArrTest {
public static void main(String[] args) {
    String[] text = new String[] { "a","#","#","b", "c", "#", "#","#", "b", "3", "3" };
    Map<Integer, List<String>> retMap = new HashMap<Integer, List<String>>();
    List<String> repeatString;
    int count = 0;
    for (int i = 1; i < text.length; i++) {
        if(text[i].equals(text[i-1])){
            repeatString = new ArrayList<String>();
            repeatString.add(text[i]);
            for(int j=i;j<text.length;j++){
                if(text[j].equals(text[i])){
                    repeatString.add(text[j]);
                } else {
                    break;
                }
            }
            retMap.put(count, repeatString);
            count++;
            i++;
        }
    }

    Iterator<Integer>iter = retMap.keySet().iterator();
    while(iter.hasNext()){
        System.out.println(retMap.get(iter.next()));
    }
}
}

Hope that helps :)

Ouput :

[#, #]
[#, #, #]
[3, 3]

score 1 · Answer 5 · answered Jul 22 '15 at 19:22

Your code, modified according to @heenenee 's answer:

List<Object> tmplist = new ArrayList<Object>();
for (int i = 0; i<array.length(); i++) {
    if (array[i].equals(#)) {
        tmplist.add(array[i]);
        if (!array[i+1].equals(#) && tmplist.size() < 2) {
            tmplist.clear();
        } else if (!array[i+1].equals(#) && tmplist.size() > 1) {
            pattern.add(tmplist);
            tmplist = new ArrayList<Object>(); // Easy changes here
        }
    }
}
//pattern is the 2d ArrayList (ArrayList which consists of ArrayLists)

JAVA fill a temporary Arraylist with objects and then add it into a ArrayList which consists of arrayLists

5 Answers5