how to compare two array of objects to remove duplicates?

Question

I am working with two array of objects to remove duplicates objects.

I have array1 of Class1.java

String name;
String number;

I added objects like below:

list1.add(new Class1("name1","number1"));
list1.add(new Class1("name2","number2"));
list1.add(new Class1("name3","number3"));
list1.add(new Class1("name4","number4"));

list2.add(new Class1("name1","number1"));
list2.add(new Class1("name5","number2"));
list2.add(new Class1("name6","number3"));
list2.add(new Class1("name2","number4"));

now I want to compare list1 and list 2 in the name basis. How can I remove duplicate elements from list1 after comparing with list 2.

Answer 1

You can remove elements in list1 that exists on list2 using the removeAll method. First you have to override the equals and hashCode methods in your class:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Class1)) return false;

    Class1 class1 = (Class1) o;

    return name.equals(class1.name);
}

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

Then after adding the elements, just use the method removeAll like this:

list1.add(new Class1("name1","number1"));
list1.add(new Class1("name2","number2"));
list1.add(new Class1("name3","number3"));
list1.add(new Class1("name4","number4"));

list2.add(new Class1("name1","number1"));
list2.add(new Class1("name5","number2"));
list2.add(new Class1("name6","number3"));
list2.add(new Class1("name2","number4"));

list1.removeAll(list2);

list1 after removing elements:

[Class1{name='name3'}, Class1{name='name4'}]

EDIT

Another way without overriding equals and hashCode is using the removeIf method (available since java 8):

list1.removeIf(c -> list2.stream()
                    .map(Class1::getName)
                    .anyMatch(n -> n.equals(c.getName())));

Here I'm removing each element on list1 whose name is equal to the name of an element on list2 .

Answer 2

Combine both list into single list and send it below custom function :

HashMap store unique key, Select any field(unique value) from own class and set that field value as key into HashMap and class object as value.

private List<Class1> clearListFromDuplicateFirstName(List<Class1> combineList) {

     Map<String, Class1> cleanMap = new LinkedHashMap<String, Class1>();
     for (int i = 0; i < combineList.size(); i++) {
          cleanMap.put(combineList.get(i).getname(), combineList.get(i));
     }

     return new ArrayList<Class1>(cleanMap.values());;
}