Given two strings str1 and str2, write code to find out if all non-unique elements in str2 are in str1?

public static Set<String> getNonUniqueChar(String str1, String str2){  
 HashMap<Character, Integer> visit = new HashMap<Character, Integer>(); // find the non-unique characters  
    HashSet<Character> visit2 = new HashSet<Character>(); // put the st1 chars into to hashset  
    for (int i=0; str2.length; i++) {  
  char c = str2.charAt(i);  
  if(visit.containsKey(c)){  
   Integer charCount = visit.get(c);  
   visit.put(c,charCount++);  
  }else  
   visit.put(c,1);//initially char count is 1  
 }  
           
    for (i=0; i < str1.length; i++){  
  char c = str1.charAt(i);  
        if(!visit2.contains(c))  
   str1.put(c);  
 }  
 //get all the elements where count is greater than 1  
 List<String> nonUniqueCharsinS2 = new ArrayList<String>();  
 for(Character c : visit.keys()) {  
  if(visit.get(c) > 1)  
   nonUniqueCharsinS2.add(c);  
 }  
   
 //iterate on s1 set to get all the elements  
 Set<String> answer = new HashSet<String>();  
    for (Character c : nonUniqueCharsinS2 )  
         if(visit2.contains(c))  
   answer.add(c);  
       
  return answer;  
}