In Java Wie entferne ich Elemente beim Iterieren einer Liste, ArrayList? (5 verschiedene Möglichkeiten)

Veröffentlicht: 2021-11-08

In Java Wie entferne ich Elemente aus ArrayList während der Iteration? list.remove(s) löst java.util.ConcurrentModificationException aus, wenn Sie ein Element aus einer ArrayList entfernen, während Sie es durchlaufen.

Lass uns anfangen.

Klasse erstellen: CrunchifyRemoveItemFromList.java

Wir werden die folgenden 5 methods , um ein Element aus ArrayList zu entfernen, während wir es durchlaufen.

Methode-1: collectionRemoveIf-Methode
Methode-2: collectionRemoveIfObjectEquals-Methode
Methode-3: collectionteratorRemove-Methode
Methode-4: listIteratorWayToRemoveElement-Methode
Methode-5: streamFilterCollectWay-Methode

Kopieren Sie den folgenden Code und speichern Sie ihn.

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

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 ) ;

}

Führen Sie einfach das obige Programm als Java-Anwendung aus und Sie werden das Ergebnis wie unten sehen. Sie werden keine Concurrent Modification Exception sehen.

Hier ist die Methode java.util.Collection.removeIf():

Ergebnis der IntelliJ IDEA-Konsole:

Wir sind letztes Jahr von Eclipse zu IntelliJ IDEA gewechselt und waren begeistert. Hier ist ein Konsolenergebnis.

/ 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

Lassen Sie mich wissen, wenn Sie beim Ausführen dieses Java-Programms auf Probleme stoßen.