Conditionally remove elements from a List in Java 8
February 14, 2015 8 Comments
Java 8 introduces a new method available for Collection types: removeif(). It accepts a predicate which defines the condition on which the elements should be removed. It returns a boolean where a true response means that at least one item has been removed and false otherwise:
Collection<String> stringStack = new Stack<>();
stringStack.add("Hello");
stringStack.add("my");
stringStack.add("dear");
stringStack.add("world");
stringStack.removeIf(s -> s.contains("ll"));
The above example will remove “Hello” from the list stack.
Note that not all collections support item removal. In that case the method will throw an UnsupportedOperationException in case an attempt is made to remove a matching element. The ArrayList is one such collection:
Collection<String> asList = Arrays.asList("hello", "my", "dear", "world");
asList.removeIf(s -> s.contains("ll"));
This will throw an exception unfortunately as the Array.asList method returns an ArrayList of type java.util.Arrays.ArrayList (which is read only and fixed size) and not the classic java.util.ArrayList (resizable and item-removable) – based on a comment by Juanito below.
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Hi,
Can I remove using two conditions? Do I have to create a distinct Predicate or merely I can use && between the conditions?
Thanks,
Cristina
Hello Cristina, I’m not sure I follow. Where do you see two conditions in this post? //Andras
Hi Andras,
Well starting from your example I was wondering if I can use two conditions. I created two distinct predicates and I used “and” function. My problem is solved.
Regards,
Cristina
I think you should state more clearly that the type returned for the method Arrays.asList is of type java.util.Arrays.ArrayList (which is read only and fixed size) and not the classical java.util.ArrayList (resizable and item-removable)
Thanks for your remark, I have updated the post. //Andras
You can fix that by using:
Collection asList = new ArrayList(Arrays.asList(“hello”, “my”, “dear”, “world”));
and that should work fine.
or…
Collection asList = new ArrayList(Arrays.asList(“hello”, “my”, “dear”, “world”));
Thx Andras,
nice example which helped me to tackle a problem of removing of an element from TreeSet