why I got Compilation Error ,when writing it in Java.Here is my code

import java.io.*;
import java.util.*;
import java.lang.*;

public class Main{
    static List<Integer> a[];
    static List<Integer> w[];
    static int metka[];
    static int cnt = 0;
    private static void builtbor(String s, int x){
        if (s.length()==0){
            metka[x] = 666;
            return;
        }
        char ch = s.charAt(0);
        for (int i = 0;i<a[x].size();i++)
            if (w[x].get(i) == (int)ch){
                builtbor(s.substring(1, s.length()),a[x].get(i));
                return;
            }
        cnt++;
        a[x].add(cnt);
        w[x].add((int)ch);
        builtbor(s.substring(1, s.length()),cnt);

    }

    private static char getchar(int x){
        return (char)x;
    }

    private static void getwords(String s, int x, String now){
        if (metka[x] == 666)
            System.out.println("  "+now);
        if (!s.isEmpty()){
        char ch = s.charAt(0);
        for (int i = 0;i<a[x].size();i++)
            if (w[x].get(i) == ch)
                getwords(s.substring(1,s.length()),a[x].get(i),now+ch);
        }
        else
        {
            for (int i = 0;i<a[x].size();i++)
                    getwords(s,a[x].get(i),now+getchar(w[x].get(i)));
        }

    }
    public static void main(String[] args) throws IOException{
        Scanner in = new Scanner(System.in);
        a = new List[2000];
        w = new List[2000];
        metka = new int[20000];
        for (int i = 0;i<2000;i++)
        {
            a[i] = new ArrayList<Integer>();
            w[i] = new ArrayList<Integer>();
        }
        while (in.hasNext()){
            String s = in.next();
            char t = s.charAt(0);
            s = s.substring(1,s.length());
            if (t=='+')
                builtbor(s,0);
            else{
                System.out.println(s);
                getwords(s,0, "");
            }
        }
    }
}