This is a pretty common question, but I could not find this part:
Say I have this array list:
List<MyDataClass> arrayList = new List<MyDataClass>;
MyDataClass{
String name;
String age;
}
Now, I need to find duplicates on the basis of age
in MyDataClass
and remove them. How is it possible using something like HashSet as described here?
I guess, we will need to overwrite equals
in MyDataClass?
I'd suggest that you override both equals
and hashCode
(HashSet
relies on both!)
To remove the duplicates you could simply create a new HashSet
with the ArrayList as argument, and then clear the ArrayList and put back the elements stored in the HashSet
.
class MyDataClass {
String name;
String age;
@Override
public int hashCode() {
return name.hashCode() ^ age.hashCode();
}
@Override
public boolean equals(Object obj) {
if (!(obj instanceof MyDataClass))
return false;
MyDataClass mdc = (MyDataClass) obj;
return mdc.name.equals(name) && mdc.age.equals(age);
}
}
And then do
List<MyDataClass> arrayList = new ArrayList<MyDataClass>();
Set<MyDataClass> uniqueElements = new HashSet<MyDataClass>(arrayList);
arrayList.clear();
arrayList.addAll(uniqueElements);
But, what if I do not have the luxury of doing that?
Then I'd suggest you do some sort of decorator-class that does provide these methods.
class MyDataClassDecorator {
MyDataClass mdc;
public MyDataClassDecorator(MyDataClass mdc) {
this.mdc = mdc;
}
@Override
public int hashCode() {
return mdc.name.hashCode() ^ mdc.age.hashCode();
}
@Override
public boolean equals(Object obj) {
if (!(obj instanceof MyDataClassDecorator))
return false;
MyDataClassDecorator mdcd = (MyDataClassDecorator) obj;
return mdcd.mdc.name.equals(mdc.name) && mdcd.mdc.age.equals(mdc.age);
}
}
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