package lambda; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.List; import java.util.Map; import java.util.Set; import java.util.stream.Collectors; public class Dog { // dog types private enum Type { PUG, BOXER, LABRADOR, HUSKY } final String name; final double weight; final Type type; private Dog(String name, double weight, Type type) { this.name = name; this.weight = weight; this.type = type; } public static Dog newPug(String name, double weight) { return new Dog(name, weight, Type.PUG); } public static Dog newBoxer(String name, double weight) { return new Dog(name, weight, Type.BOXER); } public static Dog newLabrador(String name, double weight) { return new Dog(name, weight, Type.LABRADOR); } public static Dog newHusky(String name, double weight) { return new Dog(name, weight, Type.HUSKY); } @Override public String toString() { return "Dog [name=" + name + ", weight=" + weight + ", type=" + type + "]"; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((name == null) ? 0 : name.hashCode()); result = prime * result + ((type == null) ? 0 : type.hashCode()); long temp; temp = Double.doubleToLongBits(weight); result = prime * result + (int) (temp ^ (temp >>> 32)); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Dog other = (Dog) obj; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; if (type != other.type) return false; if (Double.doubleToLongBits(weight) != Double.doubleToLongBits(other.weight)) return false; return true; } public static void main(String[] args) { List dogs = new ArrayList<>(); dogs.add(Dog.newBoxer("boxer1", 15)); dogs.add(Dog.newBoxer("boxer2", 16)); dogs.add(Dog.newBoxer("boxer3", 13)); dogs.add(Dog.newBoxer("boxer4", 14)); dogs.add(Dog.newBoxer("boxer5", 15)); dogs.add(Dog.newHusky("husky1", 18)); dogs.add(Dog.newHusky("husky2", 19)); dogs.add(Dog.newHusky("husky3", 17)); dogs.add(Dog.newHusky("husky4", 18)); dogs.add(Dog.newHusky("husky5", 20)); dogs.add(Dog.newLabrador("labrador1", 17)); dogs.add(Dog.newLabrador("labrador2", 18)); dogs.add(Dog.newLabrador("labrador3", 19)); dogs.add(Dog.newLabrador("labrador4", 20)); dogs.add(Dog.newLabrador("labrador5", 17)); dogs.add(Dog.newPug("pug1", 10)); dogs.add(Dog.newPug("pug2", 11)); dogs.add(Dog.newPug("pug3", 9)); dogs.add(Dog.newPug("pug4", 11)); dogs.add(Dog.newPug("pug5", 10)); Collections.shuffle(dogs); System.out.println(dogs.size()); /* * Exemple 1 * * map/mapToDouble/forEach */ System.out.println("======Exemple1======"); // size System.out.printf("count %d%n", dogs.stream().count()); // max weight System.out.printf("max %f%n", dogs.stream().mapToDouble(dog -> dog.weight).max().orElse(-1)); // min weight System.out.printf("min %f%n", dogs.stream().mapToDouble(dog -> dog.weight).min().orElse(-1)); // average weight System.out.printf("average %f%n", dogs.stream().mapToDouble(dog -> dog.weight).average().orElse(-1)); // ^^^^^ dogs.stream() makes a stream of objects, and mapToDouble means // I want convert objects to double, // if you want, you can, of cause use map in the place of mapToDouble, // the strength point of using mapToDouble is you can use .max() .min() // etc // by using map, you have to do it by yourself, there is an exemple System.out.printf("max by reduce %f%n", dogs.stream().map(dog -> { return dog.weight; }).reduce((x, y) -> { return x > y ? x : y; }).orElse(-1.0)); dogs.stream().forEach(System.out::println); // same as // dogs.stream().forEach(dog -> System.out.println(dog)); /* * Exemple 2 filter/ collect */ System.out.println("======Exemple2======"); // all pug in a list List pugs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.PUG)).collect(Collectors.toList()); // all lab in an ArrayList List labs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.LABRADOR)) .collect(Collectors.toCollection(ArrayList::new)); // all boxer in a set Set boxs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.BOXER)).collect(Collectors.toSet()); // all husky in a map Map husk = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.HUSKY)) .collect(Collectors.toMap(dog -> (dog.name), item -> item)); System.out.println(pugs); System.out.println(labs); System.out.println(boxs); System.out.println(husk); /* * Exemple 3 filter/collect/ sorted */ System.out.println("======Exemple3======"); // I sorted them by name // all pug in a list pugs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.PUG)) .sorted((x, y) -> x.name.compareToIgnoreCase(y.name)).collect(Collectors.toList()); // all lab in an ArrayList labs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.LABRADOR)) .sorted((x, y) -> x.name.compareToIgnoreCase(y.name)).collect(Collectors.toCollection(ArrayList::new)); System.out.println(pugs); System.out.println(labs); // I sorted them by weight // all pug in a list pugs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.PUG)) .sorted((x, y) -> Double.compare(x.weight, y.weight)).collect(Collectors.toList()); // all lab in an ArrayList labs = dogs.stream().filter(dog -> dog.type.equals(Dog.Type.LABRADOR)) .sorted((x, y) -> Double.compare(x.weight, y.weight)).collect(Collectors.toCollection(ArrayList::new)); System.out.println(pugs); System.out.println(labs); /* * Exemple 4 * flatMap */ //now I'm going to merge all these collections to a list List> collections = Arrays.asList(pugs,labs, boxs, husk.values()); //they are the same List dogs2 = collections.stream().flatMap(collection -> collection.stream()).collect(Collectors.toList()); collections.stream().flatMap(Collection::stream).collect(Collectors.toList()); //now they are back to a list again System.out.println(dogs2); System.out.printf("%d%n", dogs2.size()); //the different between map and flatMap, is map() returns only a value, flatMap can return //a stream that has a lot of values, so in my exemple, flatMap(Stream::of) means //each collection became a stream, and collect will be applied in each element of those streams. //show you if they are the same System.out.println(dogs2.containsAll(dogs) && dogs.containsAll(dogs2)); } }