How to Iterate over a Set HashSet without an Iterator

Question

How can I iterate over a Set HashSet without the following   Iterator iter   set iterator    while  iter hasNext          System out println iter next

User · Answer

Enumeration      Enumeration e   new Vector set  elements    while  e hasMoreElements                  System out println e nextElement             Another way  java util Collections enumeration      for  Enumeration e1   Collections enumeration set   e1 hasMoreElements                   System out println e1 nextElement             Java 8   set forEach element - gt  System out println element      or  set stream   forEach  elem  - gt        System out println elem

User · Answer

There are at least six additional ways to iterate over a set  The following are known to me   Method 1     Obsolete Collection Enumeration e   new Vector movies  elements    while  e hasMoreElements        System out println e nextElement         Method 2  for  String movie   movies      System out println movie       Method 3  String   movieArray   movies toArray new String movies size      for  int i   0  i  lt  movieArray length  i        System out println movieArray i        Method 4     Supported in Java 8 and above movies stream   forEach  movie  - gt      System out println movie         Method 5     Supported in Java 8 and above movies stream   forEach movie - gt  System out println movie      Method 6     Supported in Java 8 and above movies stream   forEach System out  println     This is the HashSet which I used for my examples   Set lt String gt  movies   new HashSet lt  gt     movies add  Avatar    movies add  The Lord of the Rings    movies add  Titanic

User · Answer

You can use an enhanced for loop   Set lt String gt  set   new HashSet lt String gt        populate set  for  String s   set        System out println s       Or with Java 8   set forEach System out  println

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Converting your set into an array may also help you for iterating over the elements   Object   array   set toArray     for int i 0  i lt array length  i       Object o   array i

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To demonstrate  consider the following set  which holds different Person objects   Set lt Person gt  people   new HashSet lt Person gt     people add new Person  Tharindu   10    people add new Person  Martin   20    people add new Person  Fowler   30         Person Model Class   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  amp  compareTo methods       The for statement has a form designed for iteration through Collections and arrays  This form is sometimes referred to as the enhanced for statement  and can be used to make your loops more compact and easy to read      for Person p people     System out println p getName           Java 8 - java lang Iterable forEach Consumer     people forEach p - gt  System out println p getName         default void forEach Consumer lt   super T gt  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

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Here are few tips on how to iterate a Set along with their performances   public class IterateSet        public static void main String   args               example Set         Set lt String gt  set   new HashSet lt  gt              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 lt String gt  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  - gt  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  - gt  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 lt String gt  splitIterator   set spliterator            splitIterator forEachRemaining  s  - gt  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             The code is self explanatory   The result of the durations are   Iterator Duration  495287 Lambda Duration  50207470 Stream Api        2427392 Split Iterator     567294   We can see the Lambda takes the longest while Iterator is the fastest

User · Answer

However there are very good answers already available for this  Here is my answer   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   Also  if this Set is of Custom class type  for eg  Customer   Set lt Customer gt  setCust   new HashSet lt  gt         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  - gt  System out println k getId       k getName       k getAge           Customer class   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

User · Answer

You can use functional operation for a more neat code   Set lt String gt  set   new HashSet lt String gt      set forEach  s  - gt         System out println s

[java] How to Iterate over a Set/HashSet without an Iterator?

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