合并没有重复项的Model元素的ArrayList

Question

Hi I have two array list List l1 and List l2, Name,age,sex,uniqID,marks are the data inside the lists. I want to join l1 and l2 without duplicates.uniqID is unique for each student. I have been looping through all the elements and comparing each and every element. But My list would have around 20k items so the looping is taking too much time. I have tried all the answers from this post nothing worked for me. Any suggestions.?

Answer 1

Simple example:

public class Person{
    int id;
    String name;
    //fields, getter, setter, constructor omited....

    @Override
    public boolean equals(Object o){
        if (!(o instanceof Person)){
            //implicit null check
            return false;
        }
        return this.id==((Person)o).id;
    }

    @Override
    public int hashCode(){
        return this.id;
    } 
}

The class Person does implement equals and hashCode now. equals is used by java for deciding if an object is a duplicate of another object. hashCode is not necessary per se, but it is suggested to override hashCode and equals together.

If both methods are implemented, you can simply use the build-in methods and datastructures in java:

With lists:

List<Person> listA = new ArrayList<>();
List<Person> listB = new ArrayList<>();
// filling the lists omitted
List<Person> mergedList=new ArrayList<>();
mergedList.addAll(listA);
mergedList.removeAll(listB);
mergedList.addAll(listB);

Or with sets:

List<Person> listA = new ArrayList<>();
List<Person> listB = new ArrayList<>();
// filling the lists omitted
Set<Person> mergedSet=new HashSet<>();
mergedSet.addAll(listA);
mergedSet.addAll(listB);

Answer 2

You can combine both the arraylist and pass it to HashSet object As Set does not contain duplicates you can do following

ArrayList<String> a=new ArrayList<String>();
ArrayList<String> b=new ArrayList<String>();

b.addAll(a);

If you want to retain the order of elements use LinkedHashSet

LinkedHashSet<String> result=new LinkedHashSet<String>(b);