Operating sublists efficiently

Question

In my Java program, I need to operate on the sublists a of ArrayList or LinkedList often, like removing a sublist, comparing two sublists.

For ArrayList or LinkedList, I didn't find any good APIs to do these. My current implementation is as below. Basically, it takes an input like:

u1234 u1236 u1236 u2def u1236 u1236 u2def

and outputs the following:

u1234 ( ( u1236 ) * u2def ) *

Core function:

ArrayList<String> toRegex(ArrayList<String> tokenArray)
{
 /* check different length of continuous duplication */
 for(int len=1; len<=tokenArray.size()/2; len++) 
 {
 boolean match = false;
 /* given a length, scan for duplication */
 for(int i=0; i<tokenArray.size()-(2*len-1); i++) 
 { 
 ArrayList<String> first = new ArrayList<String>();
 ArrayList<String> second = new ArrayList<String>();
 for(int j=i; j<i+len; j++)
 first.add(tokenArray.get(j));
 for(int j=i+len; j<i+2*len; j++)
 second.add(tokenArray.get(j)); 
 if(isSpecial(first)) { /* skip the cases */
 continue;
 }
 while(isIdentical(first, second))
 {
 match = true;
 for(int j=i+len; j<i+2*len; j++)
 tokenArray.remove(i+len);
 if(i+2*len > tokenArray.size())
 break;
 second.clear();
 for(int j=i+len; j<i+2*len; j++)
 second.add(tokenArray.get(j));
 }
 if(match == true) {
 tokenArray.add(i, "(");
 tokenArray.add(i+1+len, ")");
 tokenArray.add(i+2+len, "*");
 i = i+3+len;
 match = false;
 } 
 }
 }
 return tokenArray;
}

Currently, the performance is not good. Could you find the bad design or inappropriate usage of data structures/APIs? What are the good common ways of operating sublists?

Answer 1

Yes, this doesn't look pretty. Consider converting the list to sets or using RegEx.

ArrayList<String> A = new ArrayList<String>();
A.add("Z");
A.add("Z");
A.add("C");
A.add("X");
A.add("Z");
Set<String> set = new HashSet<String>(A);
for(String temp:set)
 System.out.println(temp); 

Sublists:

List<String> subList = alist.subList(2, 4);

Use retainAll to get intersections:

listOne.retainAll(listTwo) ; 
boolean areEqualNotSamePosition = listeOne.size();

Answer 2

public static void main(final String[] args) {
 final String[] tabS = "u1234 u1236 u1236 u2def u1236 u1236 u2def "
 .split(" ");
 // The same thing can be done/adapted with a String[]
 final ArrayList<String> al = new ArrayList<>();
 final ArrayList<String> alTmp = new ArrayList<>();
 for (final String s : tabS) {
 al.add(s);
 }
 // removing need to begin by end
 for (int i = al.size() - 1; i >= 0; i--) {
 final String string = al.get(i);
 if (!alTmp.contains(string)) {
 alTmp.add(string);
 } else {
 al.remove(i);
 }
 }
 // inserting decoration if result have 2 or more object
 final int j = al.size();
 final String ending = ")*";
 if (j > 1) {
 for (int i = 1; i < j; i++) {
 al.add(1, "(");
 }
 for (int i = al.size() - 1; i > j; i--) {
 al.add(i, ending);
 }
 al.add(ending);
 }
 System.out.println(al.toString());
 }

Output : [u1234, (, (, u1236, )*, u2def, )*]
You can use a StringBuilder to remove ''' and make the output as you like.