I want to retrive index of specific element of my list :
ArrayList<Field> list = new ArrayList<Field>();
list.addAll(profile.getFieldsList());
Object privacyName = "privacy";
int i = list.indexOf(privacyName);
boolean doesContain = list.contains(privacyName);
There is a field containing "privacy" in the list but i is always -1 and doesContain is always false. Why this search doesn't work ?
Why this search doesn't work ?
Because list contains instances of the Field class and you are calling the contains method passing a String instance.
To make it work you need to pass an instance of the Field class.
String which can't possibly be a Field. public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
You need to override equals for logical equality or rely on default for reference equality.
In this case privacyName.equals(elementData[i]) is always false.
From the Java docs for indexOf:
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
So your list does not contain the object privacyName;
In ArrayList Index of method will based on equals method. In field class overide equals and hasCode method of Object class. And you told that "There is a field containing "privacy" in the list" . IndexOf Array will based on equals method. As @rocketboy's ans, u need to overide equals as well as hasCode method properly. Why do I need to override the equals and hashCode methods in Java?
Field, which cannot have the value"privacy". Do you have some property ofField, for which you are having that value?