Java – Remove duplicates in the ArrayList of custom objects

I’m trying to remove duplicate objects from an array.

I have my habit, and it consists of two doubles: x and y.

What I want to do is remove duplicates ((x &&y) == (x1 &

& y1)) if x == x1 I want to keep objects with higher y.

ArrayList<MyObject> list = [x(0),y(0)], [x(0),y(0)], [x(0.5),y(0.5], [x(0.5),y(0.6)], [x(1),y(1)]; 
ArrayList<MyObject> results = [x(0),y(0)], [x(0.5),y(0.6)], [x(1),y(1)]; 

I

tried implementing the equals method, but I don’t know how to use it :

public boolean equals(Object obj) {
    if (obj == null || !( obj instanceof MyObject)) {
        return false;
    }
    return (this.x == ((MyObject)obj).x);
}

Lists are always sorted using Collections.sort by x.

Thank you.

Given MyObject:: like this

class MyObject {
    private final double x;
    private final double y;

public MyObject(double x, double y) {
        this.x = x;
        this.y = y;
    }

@Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

MyObject myObject = (MyObject) o;

if (Double.compare(myObject.x, x) != 0) return false;
        if (Double.compare(myObject.y, y) != 0) return false;

return true;
    }

@Override
    public int hashCode() {
        int result;
        long temp;
        temp = Double.doubleToLongBits(x);
        result = (int) (temp ^ (temp >>> 32));
        temp = Double.doubleToLongBits(y);
        result = 31 * result + (int) (temp ^ (temp >>> 32));
        return result;
    }
}

You can implement a unique method that returns a list of only unique elements:

private List<MyObject> unique(List<MyObject> list) {
    List<MyObject> uniqueList = new ArrayList<>();
    Set<MyObject> uniqueSet = new HashSet<>();
    for (MyObject obj : list) {
        if (uniqueSet.add(obj)) {
            uniqueList.add(obj);
        }
    }
    return uniqueList;
}

and unit test it to verify that it works:

@Test
public void removeDups() {
    List<MyObject> list = Arrays.asList(new MyObject(0, 0), new MyObject(0, 0), new MyObject(0.5, 0.5), new MyObject(0.5, 0.6), new MyObject(1, 1));
    List<MyObject> results = Arrays.asList(new MyObject(0, 0), new MyObject(0.5, 0.5), new MyObject(0.5, 0.6), new MyObject(1, 1));
    assertEquals(results, unique(list));
}

Note: It is important to implement equals and hashCode
Because HashMap is used. But you should always do this in your custom class: provide the appropriate equals and hashCode implementation. By the way, I didn’t write those equals and hashCode methods. I have my IDE (IntelliJ) automatically generate them from the fields x and y of the class.