Check if a list of objects contain a specified object java

Question

Suppose there are few classes all extending an abstract class abc :-

public class mno extends abc { ... }
public class pqr extends abc { ... }
public class xyz extends abc { ... }

there is a list of objects which contains object of these class.

List<abc> f =new ArrayList<abc>();
f.add(new mno());
f.add(new pqr());
f.add(new xyz());

Is there a way to check if list f contains an object of class xyz and remove it from the list.

I tried f.contains(xyz.class) or f.contains(new xyz()) but it returned flase

I have to wonder if this is an [XY Problem](http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem) where you may be better off using a completely different approach, such as a different collection or collections. — Hovercraft Full Of Eels, Mar 18 '17 at 20:15
And beyond that : read about java coding conventions. Class names start upper case. Always. — GhostCat, Mar 18 '17 at 20:17
@GhostCat Thanks for pointing the issue, have started reading clean code by Robert Martin, and have realized my mistake after reading two chapters. — rcipher222, Mar 26 '17 at 19:20

score 4 · Answer 1 · answered Mar 18 '17 at 20:19

4

If you use java 8 you can do it:

f.removeIf(xyz.class::isInstance);

answered Mar 18 '17 at 20:19

Roma Khomyshyn

1,112
6
9

score 1 · Answer 2 · answered Mar 18 '17 at 20:19

1

You could use Java 8 Streams.

List<abc> newList = new ArrayList<>(f)
            .stream()
            .filter(xyz.class::isInstance)
            .collect(Collectors.toList());

answered Mar 18 '17 at 20:19

alayor

4,537
6
27
47

score 0 · Answer 3 · answered Mar 18 '17 at 20:17

You need to use instanceof operator to check that an object is of specific type as shown below:

 Iterator<abc> iterator = f.iterator();
    while(iterator.hasNext()) {
       if(iterator.next() instanceof xyz) {
           iterator.remove();
       }
   }

Also, the above code uses Iterator to safely remove the objects from the list.

Also, I strongly suggest you follow the Java naming conventions for class, variable, etc. as your example class names abc, xyz, etc. are very poor.

Check if a list of objects contain a specified object java

3 Answers3