Java generics method to filter and find first element in list

user_2266807 0
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private Feature findFeature(String name, List<Feature> list) {
    for (Feature item : list) {
        if (item.getName().equals(name)) {
            return  item;
        }
    }
    return null;
}

I have 10 other methods like this. Same signature, same logic. Only different is that List parameter is using different objects, e.g. List<Data> list, or List<Option> list, etc. All objects has a getName() method in it. I want to create a generic method and remove all others.

If I use something like this,

private <T> T findInList(String name, List<T> list) {

I don't have access the getName() method. What is the easiest way to create this method? Is reflection api the only option?

EDIT:

I found the mistake I did. It is working just fine like this:

for (FeatureEntity entity : data.getFeatures()) {
    Predicate<Feature> filter = f -> f.getName().equalsIgnoreCase(entity.getName());
    if (entity.getFeatureId() != null && findInList(featureList, filter) == null) {
        FeatureEntity n = new FeatureEntity();
        n.setId(entity.getId());
        // ...
    }
}
generics java
3 Answers

You can create generic method that takes generic list with Predicate to get the first matching item after filtering

private <T> T findFeature(List<T> list, Predicate<T> predicate) {
    return list.stream().filter(predicate).findFirst().orElse(null);
}

And then create Predicate with required type and call that method 

Predicate< Feature > filter = f->f.getName().equalsIgnoreCase(name);
findFeature(list,filter);

On another side, you can also return Optional<T> instead of null when no element is found:

private <T> Optional<T> findFeature(List<T> list, Predicate<T> predicate) {
    return list.stream().filter(predicate).findFirst();
}
user_99591520

You could create a common Named interface, like

public interface Named {
    String getName();
}

Then use a wildcard to specify that the method requires that Named interface.

private <T extends Named> T findInList(String name, List<T> list)

Then you can use getName. Of course, you need to modify the classes you wish to use to implements Named (but you mentioned they all already have getName() methods).

user_29709470

first, you need an Inferface:

public interface HasName {
    String getName();
}

then, your Feature class has to implement it:

public class Feature implements HasName {

After you add the implements to your class name, you need to implement the getName() method (let your IDE help you with this)

then go as follows:

private <T extends HasName> findFeature(String name, List<T> list) {
    // Do your logic, getName will be availible here.
}
user_23553920
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