Max length AltArray

Problem : An array which contains the alternating elements (non-zero) of opposite sign is called as Alt array. Given an array, find the maximum length of sub-array which is AltArray. (Keep it O(N))

E.g. {908,-7654,102354,9,102,-349,25,910987,-11,100,10}
have three sub-array which are AltArray and have a max length of 3, viz. {908,-7654,102354}, {102,-349,25}, {910987,-11,100}.

/*An array which contains the alternating elements (non-zero) of opposite sign is called as Alt array. 
Given an array, find the maximum length of an array which is alternate array. */

public class AltArr{
 static public void main(String...y){
  
  System.out.println(getMaxLength(new long[]{3,-78,9,-18,98,-120,100,1023,-11,12,13})); //7
  System.out.println(getMaxLength(new long[]{1023,-1903,109876,-198})); //4
  System.out.println(getMaxLength(new long[]{10000})); //1
  System.out.println(getMaxLength(new long[]{213,-6100,100987,-2900009,1120,-10,914,-212,101,-815,1})); //11
  System.out.println(getMaxLength(new long[]{908,-7654,102354,9,102,-349,25,910987,-11,100,10})); //3
  System.out.println(getMaxLength(new long[]{1,-1,1,1,1,-1,1,1,-1,1,-1})); //4
 }
 
  static long getMaxLength(long[] a){
  long oldMaxLength = 1, newMaxLength = 1;
  for(int i=1 ; i < a.length ; i++)
  {
   if(a[i]*a[i-1] < 0)
    newMaxLength++;
   else{
    if(newMaxLength > oldMaxLength)
     oldMaxLength = newMaxLength;
    newMaxLength = 1;
   }
  }
  
  return oldMaxLength > newMaxLength ? oldMaxLength : newMaxLength;
 }
}

Print all the characters present in the given string only once in a reverse order. Time & Space complexity should not be more than O(N).

/*An array which contains the alternating elements (non-zero) of opposite sign is called as Alt array. 
Given an array, find the maximum length of an array which is alternate array. */

/* 
e.g. 
1)Given a string aabdceaaabbbcd 
the output should be - dcbae 
2)Sample String - aaaabbcddddccbbdaaeee 
Output - eadbc 
3)I/P - aaafffcccddaabbeeddhhhaaabbccddaaaa 
O/P - adcbhef 
*/
public class PrintOnceReversed{
 public static void main(String...q){
  System.out.println(printReverse("aabdceaaabbbcd")); //dcbae
  System.out.println(printReverse("aaafffcccddaabbeeddhhhaaabbccddaaaa")); //adcbhef
  System.out.println(printReverse("aaaabbcddddccbbdaaeee")); //eadbc 
 }
 
 static String printReverse(String str){
  str = new StringBuffer(str).reverse().toString();
  boolean charArr []= new boolean[255];
  String revStr = "";
  for(int i=0 ; i<charArr.length ; i++)
   charArr[i] = false;
  
  for(int i=0 ; i<str.length() ; i++)
  {
   if(!charArr[str.charAt(i)])
   {
    revStr = revStr + str.charAt(i);
    charArr[str.charAt(i)] = true;
   } 
  }

   return revStr;
 }
}