How to search in a List of Java object

Question

I have a List of object and the list is very big. The object is

class Sample {
    String value1;
    String value2;
    String value3;
    String value4;
          


        

Answer 1

Using Java 8

With Java 8 you can simply convert your list to a stream allowing you to write:

import java.util.List;
import java.util.stream.Collectors;

List list = new ArrayList();
List result = list.stream()
    .filter(a -> Objects.equals(a.value3, "three"))
    .collect(Collectors.toList());

Note that

• a -> Objects.equals(a.value3, "three") is a lambda expression
• result is a List with a Sample type
• It's very fast, no cast at every iteration
• If your filter logic gets heavier, you can do list.parallelStream() instead of list.stream() (read this)

Apache Commons

If you can't use Java 8, you can use Apache Commons library and write:

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.Predicate;

Collection result = CollectionUtils.select(list, new Predicate() {
     public boolean evaluate(Object a) {
         return Objects.equals(((Sample) a).value3, "three");
     }
 });

// If you need the results as a typed array:
Sample[] resultTyped = (Sample[]) result.toArray(new Sample[result.size()]);

Note that:

• There is a cast from Object to Sample at each iteration
• If you need your results to be typed as Sample[], you need extra code (as shown in my sample)

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Bonus: A nice blog article talking about how to find element in list.