Bagaimana cara Iterate melalui Set / HashSet tanpa Iterator?

Bagaimana saya bisa mengulangi Set/ HashSettanpa yang berikut ini?

Iterator iter = set.iterator();
while (iter.hasNext()) {
    System.out.println(iter.next());
}

Anda dapat menggunakan loop yang disempurnakan untuk :

Set<String> set = new HashSet<String>();

//populate set

for (String s : set) {
    System.out.println(s);
}

Atau dengan Java 8:

set.forEach(System.out::println);

Setidaknya ada enam cara tambahan untuk beralih pada satu set. Berikut ini diketahui oleh saya:

Metode 1

// Obsolete Collection
Enumeration e = new Vector(movies).elements();
while (e.hasMoreElements()) {
  System.out.println(e.nextElement());
}

Metode 2

for (String movie : movies) {
  System.out.println(movie);
}

Metode 3

String[] movieArray = movies.toArray(new String[movies.size()]);
for (int i = 0; i < movieArray.length; i++) {
  System.out.println(movieArray[i]);
}

Metode 4

// Supported in Java 8 and above
movies.stream().forEach((movie) -> {
  System.out.println(movie);
});

Metode 5

// Supported in Java 8 and above
movies.stream().forEach(movie -> System.out.println(movie));

Metode 6

// Supported in Java 8 and above
movies.stream().forEach(System.out::println);

Inilah HashSetyang saya gunakan untuk contoh saya:

Set<String> movies = new HashSet<>();
movies.add("Avatar");
movies.add("The Lord of the Rings");
movies.add("Titanic");

Mengubah set Anda menjadi array juga dapat membantu Anda untuk mengulangi elemen-elemen:

Object[] array = set.toArray();

for(int i=0; i<array.length; i++)
   Object o = array[i];

Untuk mendemonstrasikan, pertimbangkan set berikut, yang menampung objek Person berbeda:

Set<Person> people = new HashSet<Person>();
people.add(new Person("Tharindu", 10));
people.add(new Person("Martin", 20));
people.add(new Person("Fowler", 30));

Kelas Model Orang

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    //TODO - getters,setters ,overridden toString & compareTo methods

}

1. Pernyataan for memiliki formulir yang dirancang untuk iterasi melalui Koleksi dan array. Formulir ini kadang-kadang disebut sebagai pernyataan yang disempurnakan, dan dapat digunakan untuk membuat loop Anda lebih ringkas dan mudah dibaca.

for(Person p:people){
  System.out.println(p.getName());
}

2. Java 8 - java.lang.Iterable.forEach (Konsumen)

people.forEach(p -> System.out.println(p.getName()));

default void forEach(Consumer<? super T> action)

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Unless otherwise specified by the implementing class, actions are performed in the order of iteration (if an iteration order is specified). Exceptions thrown by the action are relayed to the caller. Implementation Requirements:

The default implementation behaves as if: 

for (T t : this)
     action.accept(t);

Parameters: action - The action to be performed for each element

Throws: NullPointerException - if the specified action is null

Since: 1.8

Anda dapat menggunakan operasi fungsional untuk kode yang lebih rapi

Set<String> set = new HashSet<String>();

set.forEach((s) -> {
     System.out.println(s);
});

Berikut adalah beberapa tips tentang cara mengembalikan Set bersama dengan kinerja mereka:

public class IterateSet {

    public static void main(String[] args) {

        //example Set
        Set<String> set = new HashSet<>();

        set.add("Jack");
        set.add("John");
        set.add("Joe");
        set.add("Josh");

        long startTime = System.nanoTime();
        long endTime = System.nanoTime();

        //using iterator
        System.out.println("Using Iterator");
        startTime = System.nanoTime();
        Iterator<String> setIterator = set.iterator();
        while(setIterator.hasNext()){
            System.out.println(setIterator.next());
        }
        endTime = System.nanoTime();
        long durationIterator = (endTime - startTime);


        //using lambda
        System.out.println("Using Lambda");
        startTime = System.nanoTime();
        set.forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationLambda = (endTime - startTime);


        //using Stream API
        System.out.println("Using Stream API");
        startTime = System.nanoTime();
        set.stream().forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationStreamAPI = (endTime - startTime);


        //using Split Iterator (not recommended)
        System.out.println("Using Split Iterator");
        startTime = System.nanoTime();
        Spliterator<String> splitIterator = set.spliterator();
        splitIterator.forEachRemaining((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationSplitIterator = (endTime - startTime);


        //time calculations
        System.out.println("Iterator Duration:" + durationIterator);
        System.out.println("Lamda Duration:" + durationLambda);
        System.out.println("Stream API:" + durationStreamAPI);
        System.out.println("Split Iterator:"+ durationSplitIterator);
    }
}

Kode ini jelas.

Hasil dari durasi adalah:

Iterator Duration: 495287
Lambda Duration: 50207470
Stream Api:       2427392
Split Iterator:    567294

Kita bisa melihat Lambdayang paling lama Iteratoradalah yang paling cepat.

Pencacahan (?):

Enumeration e = new Vector(set).elements();
while (e.hasMoreElements())
    {
        System.out.println(e.nextElement());
    }

Cara lain (java.util.Collections.enumeration ()):

for (Enumeration e1 = Collections.enumeration(set); e1.hasMoreElements();)
    {
        System.out.println(e1.nextElement());
    }

Java 8:

set.forEach(element -> System.out.println(element));

atau

set.stream().forEach((elem) -> {
    System.out.println(elem);
});

Namun ada jawaban yang sangat bagus sudah tersedia untuk ini. Inilah jawaban saya:

1. set.stream().forEach(System.out::println); // It simply uses stream to display set values
2. set.forEach(System.out::println); // It uses Enhanced forEach to display set values

Juga, jika Set ini adalah tipe kelas Kustom, misalnya: Pelanggan.

Set<Customer> setCust = new HashSet<>();
    Customer c1 = new Customer(1, "Hena", 20);
    Customer c2 = new Customer(2, "Meena", 24);
    Customer c3 = new Customer(3, "Rahul", 30);

setCust.add(c1);
setCust.add(c2);
setCust.add(c3);
    setCust.forEach((k) -> System.out.println(k.getId()+" "+k.getName()+" "+k.getAge()));

// Kelas pelanggan:

class Customer{
private int id;
private String name;
private int age;

public Customer(int id,String name,int age){
this.id=id;
this.name=name;
this.age=age;
} // Getter, Setter methods are present.}