في Java كيفية إزالة العناصر أثناء تكرار قائمة ، ArrayList؟ (5 طرق مختلفة)

نشرت: 2021-11-08
في Java كيفية إزالة العناصر أثناء تكرار قائمة ، ArrayList؟ (5 طرق مختلفة)

في Java كيفية إزالة العناصر من ArrayList أثناء التكرار؟ ستؤدي القائمة (الإزالة) إلى ظهور java.util.ConcurrentModificationException ، إذا قمت بإزالة عنصر من ArrayList أثناء تكراره.

هيا بنا نبدأ.

إنشاء فئة: CrunchifyRemoveItemFromList.java

سنستخدم أدناه 5 methods لإزالة عنصر من ArrayList أثناء تكرار ذلك.

  • الطريقة الأولى: طريقة collectionRemoveIf
  • الطريقة الثانية: طريقة collectionRemoveIfObjectEquals
  • الطريقة الثالثة: طريقة الإزالة Collectionterator
  • الطريقة الرابعة: طريقة listIteratorWayToRemoveElement
  • الطريقة الخامسة: طريقة StreamFilterCollectWay

انسخ الكود أدناه واحفظه.

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package crunchify . com . java . tutorials ;
 
import java . util . ArrayList ;
import java . util . List ;
import java . util . ListIterator ;
import java . util . Objects ;
import java . util . stream . Collectors ;
 
/**
* @author Crunchify.com
* In Java How to remove Elements while Iterating a List? (5 different ways to remove items)
*/
 
public class CrunchifyRemoveItemFromList {
 
     public static void main ( String [ ] args ) {
 
         collectionRemoveIfMethod ( ) ;
         collectionRemoveIfObjectEqualsMethod ( ) ;
         collectionteratorRemoveMethod ( ) ;
         listIteratorWayToRemoveElement ( ) ;
         streamFilterCollectWay ( ) ;
 
     }
 
     // Method-1: collectionRemoveIfMethod to remove elements from ArrayList
     private static void collectionRemoveIfMethod ( ) {
         List < String > crunchifyList = new ArrayList < > ( ) ;
         crunchifyList . add ( "Google.com" ) ;
         crunchifyList . add ( "Crunchify.com" ) ;
         crunchifyList . add ( "Facebook.com" ) ;
         crunchifyList . add ( "Apple.com" ) ;
 
         // removeIf(): Removes all of the elements of this collection that satisfy the given predicate.
         // Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.
         crunchifyList . removeIf ( "Apple.com" : : equals ) ;
 
         // equals(): Compares this string to the specified object.
         // The result is true if and only if the argument is not null and is a
         // String object that represents the same sequence of characters as this object.
         // For finer-grained String comparison, refer to java.text.Collator.
 
         System . out . print ( "Method-1 Result: " ) ;
         crunchifyPrint ( crunchifyList ) ;
     }
 
     // Simple print function
     private static void crunchifyPrint ( List < String > crunchifyList ) {
 
         System . out . println ( crunchifyList ) ;
     }
 
     // Method-2: collectionRemoveIfObjectEqualsMethod to remove elements from ArrayList
     private static void collectionRemoveIfObjectEqualsMethod ( ) {
         List < String > crunchifyList = new ArrayList < > ( ) ;
         crunchifyList . add ( "Google.com" ) ;
         crunchifyList . add ( "Crunchify.com" ) ;
         crunchifyList . add ( "Facebook.com" ) ;
         crunchifyList . add ( "Apple.com" ) ;
 
         // removeIf() Params:
         // filter – a predicate which returns true for elements to be removed
         // Returns:
         // true if any elements were removed
         // Throws:
         // NullPointerException – if the specified filter is null
         crunchifyList . removeIf ( crunchify - >
                 Objects . equals ( crunchify ,
                         "Crunchify.com" ) | |
                         Objects . equals ( crunchify , "Apple.com" ) ) ;
 
         System . out . print ( "Method-2 Result: " ) ;
         crunchifyPrint ( crunchifyList ) ;
     }
 
     // Method-3: collectionteratorRemoveMethod to remove elements from ArrayList
     private static void collectionteratorRemoveMethod ( ) {
         List < String > crunchifyList = new ArrayList < > ( ) ;
         crunchifyList . add ( "Google.com" ) ;
         crunchifyList . add ( "Crunchify.com" ) ;
         crunchifyList . add ( "Facebook.com" ) ;
         crunchifyList . add ( "Apple.com" ) ;
 
         // listIterator(): Returns a list iterator over the elements in this list (in proper sequence).
         ListIterator < String > crunchifyIterator = crunchifyList . listIterator ( ) ;
 
         // hasNext(): Returns true if this list iterator has more elements when traversing the list in the forward direction.
         // (In other words, returns true if next would return an element rather than throwing an exception.)
         while ( crunchifyIterator . hasNext ( ) ) {
 
             // equals(): Compares this string to the specified object.
             // The result is true if and only if the argument is not null and is a
             // String object that represents the same sequence of characters as this object.
             //For finer-grained String comparison, refer to java.text.Collator.
             if ( "Crunchify.com" . equals ( crunchifyIterator . next ( ) ) ) {
                 // next(): returns the next element in the list and advances the cursor position.
                 // This method may be called repeatedly to iterate through the list, or intermixed with calls to previous to go back and forth.
                 // (Note that alternating calls to next and previous will return the same element repeatedly.)
 
                 crunchifyIterator . remove ( ) ;
                 // remove(): Removes from the list the last element that was returned by next or previous (optional operation).
                 // This call can only be made once per call to next or previous. It can be made only if add has not been called after the last call to next or previous.
             }
         }
 
         System . out . print ( "Method-3 Result: " ) ;
         crunchifyPrint ( crunchifyList ) ;
     }
 
     // Method-4: listIteratorWayToRemoveElement to remove elements from ArrayList
     private static void listIteratorWayToRemoveElement ( ) {
         List < String > crunchifyList = new ArrayList < > ( ) ;
         crunchifyList . add ( "Google.com" ) ;
         crunchifyList . add ( "Crunchify.com" ) ;
         crunchifyList . add ( "Facebook.com" ) ;
         crunchifyList . add ( "Apple.com" ) ;
 
         List < String > crunchifyNewList = new ArrayList < > ( ) ;
         for ( String s : crunchifyList ) {
             if ( ! "Facebook.com" . equals ( s ) ) {
                 crunchifyNewList . add ( s ) ;
             }
         }
 
         System . out . print ( "Method-4 Result: " ) ;
         crunchifyPrint ( crunchifyNewList ) ;
     }
 
     // Method-5: streamFilterCollectWay to remove elements from ArrayList
     private static void streamFilterCollectWay ( ) {
 
         List < String > crunchifyList = new ArrayList < > ( ) ;
         crunchifyList . add ( "Google.com" ) ;
         crunchifyList . add ( "Crunchify.com" ) ;
         crunchifyList . add ( "Facebook.com" ) ;
         crunchifyList . add ( "Apple.com" ) ;
 
         // stream(): Returns a sequential Stream with this collection as its source.
         // This method should be overridden when the spliterator() method cannot return a spliterator
         // that is IMMUTABLE, CONCURRENT, or late-binding. (See spliterator() for details.)
 
         // filer(): Returns a stream consisting of the elements of this stream that match the given predicate.
         // This is an intermediate operation.
         List < String > crunchifyNewList = crunchifyList .
                 stream ( ) .
                 filter ( crunchify - > ! "Crunchify.com" .
                         equals ( crunchify ) )
                 . collect ( Collectors . toList ( ) ) ;
 
         // toList(): Returns a Collector that accumulates the input elements into a new List.
         // There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned;
         // if more control over the returned List is required, use toCollection(Supplier).
 
         System . out . print ( "Method-5 Result: " ) ;
         crunchifyPrint ( crunchifyNewList ) ;
     }
 
}

ما عليك سوى تشغيل البرنامج أعلاه كتطبيق Java وسترى النتيجة على النحو التالي. لن ترى استثناء التعديل المتزامن.

إليك طريقة java.util.Collection.removeIf ():

java.util.Collection removeIf Function

نتيجة وحدة التحكم IntelliJ IDEA:

انتقلنا إلى IntelliJ IDEA من Eclipse العام الماضي وأحببناه. هذه نتيجة وحدة التحكم.

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/ Users / app / Library / Java / JavaVirtualMachines / openjdk - 17.0.1 / Contents / Home / bin / java -- enable - preview - javaagent : / Applications / IntelliJ IDEA . app / Contents / lib / idea_rt . jar crunchify . com . java . tutorials . CrunchifyRemoveItemFromList
Method - 1 Result : [ Google . com , Crunchify . com , Facebook . com ]
Method - 2 Result : [ Google . com , Facebook . com ]
Method - 3 Result : [ Google . com , Facebook . com , Apple . com ]
Method - 4 Result : [ Google . com , Crunchify . com , Apple . com ]
Method - 5 Result : [ Google . com , Facebook . com , Apple . com ]
 
Process finished with exit code 0
 

اسمحوا لي أن أعرف إذا كنت تواجه أي مشكلة في تشغيل برنامج Java هذا.