Check if one list contains an element from the other

Use Java stream and anyMatch

Dealing with complex shapes or to compare specific properties, Java streams become our powerful tool:

boolean found = list1.stream().anyMatch(element -> list2.contains(element));
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The anyMatch() function stops as soon as it finds a match, acting like our very own superhero, Flash, saving processing power.

Optimizing property comparison

When your objects come with complex fields, perhaps you want to compare a specific attribute:

Set<PropertyType> properties = list2.stream()
                                     .map(ObjectType::getProperty)
                                     .collect(Collectors.toSet());

boolean found = list1.stream()
                     .map(ObjectType::getProperty)
                     .anyMatch(properties::contains);
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The speedily swift Set of properties allows for a quick check against elements from the second list.

Beware of retainAll

retainAll() might feel tempting to use, but remember it's a shady character, altering the list it's called upon. Here's an alternative that doesn't change the original list:

List<Type> copy = new ArrayList<>(list1);
copy.retainAll(list2);
boolean found = copy.size() > 0;


Guard your list against unwanted changes like a Spartan protecting its homeland!

Tap into Apache Commons

The Apache Commons' library is the James Bond of collection operations: stylish, efficient, and loaded with handy tools:

boolean found = CollectionUtils.containsAny(list1, list2);
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Wrapped in a single, suave call, it checks for common elements in a collection.

Check Long objects with care

When specifically dealing with Long attributes, correct implementation of your equals() and hashCode() methods works like well-oiled gears in machine:

Set<Long> list2Ids = list2.stream()
                           .map(ObjectType::getId)
                           .collect(Collectors.toSet());

boolean found = list1.stream()
                     .map(ObjectType::getId)
                     .anyMatch(list2Ids::contains);


Mapping objects to their IDs allows race-car speed comparisons with the efficient set.

Custom attribute comparisons

For a unique attribute, don't forget to:

@Override
public boolean equals(Object o) { /* custom equality based on an attribute */ }
@Override
public int hashCode() { /* hash code based on the same attribute */ }


This empowers collections like Sets and Maps to determine uniqueness and presence. Like finding Waldo in a crowd, it's easier if you know what he looks like!