Java Language Lambda Expressions Using lambda expressions & predicates to get a certain value(s) from a list
Example
Starting with Java 8, you can use lambda expressions & predicates.
Example: Use a lambda expressions & a predicate to get a certain value from a list. In this example every person will be printed out with the fact if they are 18 and older or not.
Person Class:
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public int getAge() { return age; }
public String getName() { return name; }
}
The built-in interface Predicate from the java.util.function.Predicate packages is a functional interface with a boolean test(T t) method.
Example Usage:
import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
public class LambdaExample {
public static void main(String[] args) {
List<Person> personList = new ArrayList<Person>();
personList.add(new Person("Jeroen", 20));
personList.add(new Person("Jack", 5));
personList.add(new Person("Lisa", 19));
print(personList, p -> p.getAge() >= 18);
}
private static void print(List<Person> personList, Predicate<Person> checker) {
for (Person person : personList) {
if (checker.test(person)) {
System.out.print(person + " matches your expression.");
} else {
System.out.println(person + " doesn't match your expression.");
}
}
}
}
The print(personList, p -> p.getAge() >= 18); method takes a lambda expression (because the Predicate is used a parameter) where you can define the expression that is needed. The checker's test method checks if this expression is correct or not: checker.test(person).
You can easily change this to something else, for example to print(personList, p -> p.getName().startsWith("J"));. This will check if the person's name starts with a "J".
