Summary - Lambda expressions

Combine lambda and method reference to write a sorting helper.

Summary - Lambda expressions

This group covered lambda expressions and method references. Lambda syntax: (parameters) -> body. Single parameter: parentheses optional; block body: return required. A lambda is assigned only to functional interfaces (one abstract method).

A method reference Class::method shortens lambdas whose body is a single method call. forEach expects a Consumer; it is the functional counterpart of the for-each loop. Comparator lambdas make sorting modern and readable.

Exercise Lambda exercise: forEach and sort

Declare List<String> names = new ArrayList<>();; add "Ayşe", "Alex", "Mehmet". Sort alphabetically with names.sort((a, b) -> a.compareTo(b));. Print with a lambda using names.forEach(s -> System.out.println(s));.

Show example solution

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

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Ayşe");
        names.add("Alex");
        names.add("Mehmet");
        names.sort((a, b) -> a.compareTo(b));
        names.forEach(s -> System.out.println(s));
    }
}

Test yourself

Match the lambda concepts

() -> ...

No-arg lambda
s -> ...

Single parameter
Class::method

Method reference
(a, b) -> a - b

Comparator lambda
Which one is a method reference?
- (a, b) -> a + b
- s -> s.length()
- Math::abs
- () -> new Object()
Show answer

Math::abs — Math::abs is a static method reference; it uses the :: token.
Match lambda vs method reference

->

Lambda arrow
::

Method reference
Runnable

No-arg target
Comparator

Sorting target

Next lesson: stream()

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