In programming, when we have a collection, sometimes we need to filter out the part that meets our requirements and discard the rest.
A detailed example is when we have a list of patient records and we want to get a list of underaged patients.
start by copying this code in a java file
public class FilteringPatients {
private static List<Patient> patientsList= Arrays.asList(
new Patient("Norman", 15,210),
new Patient("kai", 17,195),
new Patient("Adam", 21,180)
);
public static class Patient{
private String name;
private int age;
private int roomNumber;
public Patient(String n,int a, int nbr) {
name=n;
age=a;
roomNumber=nbr;
}
public int getAge() {
return age;
}
}
}
The requirement here is for the age to be below 18.
public static List<Patient> filterUnderagedPatients ( List<Patient> patientsList){
List<Patient> Underaged_Patients= new ArrayList<Patient>();
for (Patient patient: patientsList) {
if(patient.getAge()<18)
Underaged_Patients.add(patient);
}
return Underaged_Patients;
}
we can go about it this way or we can use the filter method.
Stream<T> filter(Predicate<? super T> predicate);
Filter is commonly used to filter a collection of objects.
The accepted parameters of the filter method is Predicate,let's take a closer look at it.
Firstly, Predicate is a functional interface, which means Predicate can be represented by a Lambda expression.
It's functional method is test(Object) which takes in one argument and returns a boolean,It is commonly used to test whether a condition is true or false.
@FunctionalInterface
public interface Predicate<T
let's take the previous example but this time we'll use the filter method with a predicate
public static class UnderagedPatientsPredicate implements Predicate<Patient> {
@Override
public boolean test(Patient patient) {
return patient.getAge()<18;
}
}
public static List<Patient > filter(Predicate<Patient > predicate){
List<Patient> Underaged_list= new ArrayList();
for (Patient patient: patientsList) {
if(predicate.test(patient))
Underaged_list.add(patient);
}
return Underaged_list;
}
let's test this in the main function
public static void main(String[] args) {
System.out.println("Using filterUnderagedPatients.");
for (Patient patient : filterUnderagedPatients(patientsList)
) {
System.out.println(patient);
}
System.out.println("Using filter with Predicate.");
for (Patient patient : filter( new UnderagedPatientsPredicate(), patientsList)
) {
System.out.println(patient);
}
}
the result is a list of underaged patients
Using filterUnderagedPatients.
Patient{name='Norman', age=15, roomNumber=210}
Patient{name='kai', age=17, roomNumber=195}
Using filter with Predicate.
Patient{name='Norman', age=15, roomNumber=210}
Patient{name='kai', age=17, roomNumber=195}
Top comments (1)
A simple yet detailed explanation, well done 👍