Replacing a HashSet Java member

Question

I have Set of that structure. I do not have duplicates but when I call: set.add(element) -> and there is already exact element I would like the old to be replaced.

import java.io.*;  public class WordInfo implements Serializable {     File plik;     Integer wystapienia;      public WordInfo(File plik, Integer wystapienia) {         this.plik = plik;         this.wystapienia = wystapienia;     }      public String toString() {     //  if (plik.getAbsolutePath().contains("src") && wystapienia != 0)             return plik.getAbsolutePath() + "\tWYSTAPIEN " + wystapienia;     //  return "";     }     @Override     public boolean equals(Object obj) {         if(this == obj) return true;         if(!(obj instanceof WordInfo)) return false;         return this.plik.equals(((WordInfo) obj).plik);     }      @Override     public int hashCode() {                 return this.plik.hashCode();     } } 

Answer 1

Do a remove before each add:

 someSet.remove(myObject);  someSet.add(myObject); 

The remove will remove any object that is equal to myObject. Alternatively, you can check the add result:

 if(!someSet.add(myObject)) {      someSet.remove(myObject);      someSet.add(myObject);  } 

Which would be more efficient depends on how often you have collisions. If they are rare, the second form will usually do only one operation, but when there is a collision it does three. The first form always does two.

Answer 2

If the set already contains an element that equals() the element you are trying to add, the new element won't be added and won't replace the existing element. To guarantee that the new element is added, simply remove it from the set first:

set.remove(aWordInfo); set.add(aWordInfo);