Согласки / Самогласки

import java.util.List;
import java.util.Scanner;

public class SoglaskiSamoglaski {
    public static DLL<Character> removeDuplicates(DLL<Character> list){
        DLLNode<Character> tmp=list.getFirst();
        DLLNode<Character> next;

        while(tmp!=null){
            next=tmp.succ;
            if(next==null)
                break;
            if(tmp.element==next.element){
                list.delete(tmp);
                tmp=next;
            }else{
                tmp=tmp.succ;
            }
        }
        return list;
    }
    public static boolean isVowel(char c){
        c=Character.toLowerCase(c);
        if(c=='a' || c=='e' || c=='o' || c=='i' || c=='u')
            return true;
        else return false;
    }
    public static void promeni(DLL<Character> list){
        list=removeDuplicates(list);

        DLLNode<Character> tmp=list.getFirst();
        boolean vowel=isVowel(tmp.element);

        while(tmp!=null){
            if(vowel){
                DLLNode<Character> next=tmp.succ;
                if(next==null)
                    break;
                while(true) {
                    if (isVowel(next.element)) {
                        DLLNode<Character> kopija = next;
                        list.delete(next);
                        next = kopija.succ;
                        if(next==null)
                            break;
                    }
                    else break;
                }
            }
            if(!vowel){
                DLLNode<Character> next=tmp.succ;
                if(next==null)
                    break;
                while(true) {
                    if (!isVowel(next.element)) {
                        DLLNode<Character> kopija = next;
                        list.delete(next);
                        next = kopija.succ;
                        if(next==null)
                            break;
                    }
                    else break;
                }
            }
            tmp=tmp.succ;
            if(tmp==null)
                break;
            vowel=isVowel(tmp.element);
        }
        System.out.println(list);
    }
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);

        String line=in.nextLine();
        DLL<Character> list=new DLL<>();
        for(int i=0;i<line.length();i++){
            list.insertLast(line.charAt(i));
        }
        promeni(list);
    }
}