Examples with Java 8 lambda expressions.

Example01.java

package org.jesperdj.lambda;

import java.util.ArrayList;
import java.util.List;

public class Example01 {

    // Using a for-loop (external iteration)
    public Iterable<String> getBestStudentsOfYear(Iterable<Student> students, int year) {
        List<String> result = new ArrayList<>();

        for (Student s : students) {
            if (s.getGraduationYear() == year && s.getScore() >= 9) {
                result.add(s.getName());
            }
        }

        return result;
    }
}

Example02.java

package org.jesperdj.lambda;

import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;

public class Example02 {

    // Using Google Guava with anonymous inner classes
    public Iterable<String> getBestStudentsOfYear(Iterable<Student> students, int year) {
        Iterable<Student> bestStudents = Iterables.filter(students, new Predicate<Student>() {
            @Override
            public boolean apply(Student s) {
                return s.getGraduationYear() == year && s.getScore() >= 9;
            }
        });

        Iterable<String> names = Iterables.transform(bestStudents, new Function<Student, String>() {
            @Override
            public String apply(Student s) {
                return s.getName();
            }
        });

        return names;
    }
}

Example03.java

package org.jesperdj.lambda;

import com.google.common.collect.Iterables;

public class Example03 {

    // Using Google Guava with lambda expressions
    public Iterable<String> getBestStudentsOfYear(Iterable<Student> students, int year) {
        Iterable<Student> bestStudents = Iterables.filter(students,
                (Student s) -> s.getGraduationYear() == year && s.getScore() >= 9);

        Iterable<String> names = Iterables.transform(bestStudents, s -> s.getName());

        return names;
    }
}

Example04.java

package org.jesperdj.lambda;

import com.google.common.collect.Iterables;

public class Example04 {

    // Using Google Guava with lambda expressions and a method reference
    public Iterable<String> getBestStudentsOfYear(Iterable<Student> students, int year) {
        Iterable<Student> bestStudents = Iterables.filter(students,
                s -> s.getGraduationYear() == year && s.getScore() >= 9);

        Iterable<String> names = Iterables.transform(bestStudents, Student::getName);

        return names;
    }
}

Student.java

package org.jesperdj.lambda;

public class Student {
    private final String name;
    private final int score;
    private final int graduationYear;

    public Student(String name, int score, int graduationYear) {
        this.name = name;
        this.score = score;
        this.graduationYear = graduationYear;
    }

    public String getName() {
        return name;
    }

    public int getScore() {
        return score;
    }

    public int getGraduationYear() {
        return graduationYear;
    }
}