Lambda Translation

Note the similarities between the inner class and the lambda.

The lambda is just the implementation of the one method every Comparator<Planet> must have, int compare(Planet, Planet).

Lambdas - Purpose and Format

A lambda is the implementation of an interface method, but without the method name or return type.

Lambdas are identified by the arrow ->. * The left side is the list of method parameters. * The right side is the method body.

(arguments) -> {method body}

Passing Code With Lambdas

We can replace the Comparator<Planet> anonymous class with a lambda.

package com.example.lambdas.examples;

import java.util.Collections;
import java.util.List;

public class PrintSortedPlanetsLambda {

  public static void main(String[] args) {
    List<Planet> planets = PlanetUtilities.getPlanets();

    /*
    // Passing anonymous instance
    Collections.sort(planets, new Comparator<Planet>() {
      public int compare(Planet a, Planet b) {
        return a.getOrbit() > b.getOrbit() ? 1 : -1;
      }
    });
    */

    // Passing lambda
    Collections.sort(planets,
        (Planet a, Planet b) -> { return a.getOrbit() > b.getOrbit() ? 1 : -1; } );

    for (Planet planet : planets) {
      System.out.println(planet);
    }
  }
}

Drill

Lambdas/com.example.lambdas.drills.LambdaTranslation

In this drill you will translate inner class definitions to lambda expressions, then use the lambda as you would each inner class.

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