How to remove duplicate elements in Array List Java

Question

I have two lists (arrayList1, arrayList2) contain duplicate objects.

Ex : Employee ( empname, email, mobile)
Employee e = new Employee();
e.setEmpName("chandu");
e.setEmail("chandu@gmail.com");
e.setMobile("9030128664");
arrayList1.add(e);


Employee e1 = new Employee();
e1.setEmpName("ramesh");
e1.setEmail("ramesh@gmail.com");
e1.setMobile("9154618845");
arrayList2.add(e);
arrayList2.add(e1);

In the above lists arrayList1 and arrayList2 contain one same object with same value. I have compared arrayList1 and arrayList2 and if they contains any duplicate elements I want to remove that duplicate element.

Can anyone suggest me how to compate two objects and remove duplicate objects

Note : I want to compare two lists with all the values (empname, email, mobile)

Implement `equals()` and `hashCode()` methods. Then you can iterate the lists and check if there are duplicates — XtremeBaumer, May 25 '18 at 13:06
Possible duplicate: ["How do I remove repeated elements from ArrayList? "](https://stackoverflow.com/questions/203984/how-do-i-remove-repeated-elements-from-arraylist) — Alex, May 25 '18 at 13:07
Another way is to use a map as a supporting object so you don't have to do a lot of iterations if you're lists grow large. — user3298823, May 25 '18 at 13:09
Could you not just combine both lists into a temporary `LinkedList` or a `Set` which will remove the duplicates? — Alex, May 25 '18 at 13:10

score 3 · Answer 1 · answered May 25 '18 at 13:07

There are several approaches, here are few that I can think of:

1. plain Java

public void removeDuplicatesFromList() {
    List<Integer> listWithDuplicates = Lists.newArrayList(0, 1, 2, 3, 0, 0);
    List<Integer> listWithoutDuplicates = new ArrayList<>(new HashSet<>(listWithDuplicates));

    assertThat(listWithoutDuplicates, hasSize(4));
}

2. with java (lambda)

public void removeDuplicatesFromList() {
    List<Integer> listWithDuplicates = Lists.newArrayList(1, 1, 2, 2, 3, 3);
    List<Integer> listWithoutDuplicates = listWithDuplicates.stream()
     .distinct()
     .collect(Collectors.toList());
}

3. with Guava

public void removeDuplicatesFromList() {
    List<Integer> listWithDuplicates = Lists.newArrayList(0, 1, 2, 3, 0, 0);
    List<Integer> listWithoutDuplicates = Lists.newArrayList(Sets.newHashSet(listWithDuplicates));

    assertThat(listWithoutDuplicates, hasSize(4));
}

Hope this helps,

This is not what is needed. He has **2** lists which can contain the same element and he wants to find those elements — XtremeBaumer, May 25 '18 at 13:09

score 0 · Answer 2 · answered May 25 '18 at 13:11

override equals method in your employee class, then you can compare two employee objects easily.. Employee.java

public class Employee {
    private String name;
    private String email;
    private String mobile;
    //setters and getters
    @Override
    public boolean equals(Object obj) {
        if (obj instanceof Employee) {
            Employee objUser = (Employee) obj;
            if(this.name.equals(objUser.getName())&&this.email.equals(objUser.getEmail())&&this.mobile.equals(objUser.getMobile()))
                return true;
        } else {
            return false;
        }
    }
}

How to remove duplicate elements in Array List Java

2 Answers2