Javaリストを反復処理する方法は？ Javaでループを反復処理する7つの方法

公開: 2020-01-01

Javaリストを反復処理する方法は？ Javaでループを反復処理する7つの異なる方法

Javaリストを反復処理する方法は？ このチュートリアルでは、ArrayList、Iterator、およびListの使用法を示します。

リストを反復処理する方法は7つあります。

  1. シンプルなForループ
  2. 拡張されたForループ
  3. イテレータ
  4. ListIterator
  5. whileループ
  6. Iterable.forEach（）util
  7. Stream.forEach（）util

Javaの例：

上記のpoint-5はstream() utilを使用しているため、以下のプログラムを実行するにはJDK13が必要です。

void java.util.stream.Stream.forEach （Consumer <？super String> action）は、このストリームの各要素に対してアクションを実行します。

CrunchifyIterateThroughList.java
Java
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package crunchify . com . tutorials ;
 
import java . util . * ;
 
/**
* @author Crunchify.com
* How to iterate through Java List? Seven (7) ways to Iterate Through Loop in Java.
* 1. Simple For loop
* 2. Enhanced For loop
* 3. Iterator
* 4. ListIterator
* 5. While loop
* 6. Iterable.forEach() util
* 7. Stream.forEach() util
*/
 
public class CrunchifyIterateThroughList {
 
     public static void main ( String [ ] argv ) {
 
         // create list
         List <String> crunchifyList = new ArrayList <String> ( ) ;
 
         // add 4 different values to list
         crunchifyList . add ( "Facebook" ) ;
         crunchifyList . add ( "Paypal" ) ;
         crunchifyList . add ( "Google" ) ;
         crunchifyList . add ( "Yahoo" ) ;
 
         // Other way to define list is - we will not use this list :)
         List <String> crunchifyListNew = Arrays . asList ( "Facebook" , "Paypal" , "Google" , "Yahoo" ) ;
 
         // Simple For loop
         System . out . println ( "==============> 1. Simple For loop Example." ) ;
         for ( int i = 0 ; i < crunchifyList . size ( ) ; i ++ ) {
             System . out . println ( crunchifyList . get ( i ) ) ;
         }
 
         // New Enhanced For loop
         System . out . println ( "\n==============> 2. New Enhanced For loop Example.." ) ;
         for ( String temp : crunchifyList ) {
             System . out . println ( temp ) ;
         }
 
         // Iterator - Returns an iterator over the elements in this list in proper sequence.
         System . out . println ( "\n==============> 3. Iterator Example..." ) ;
         Iterator <String> crunchifyIterator = crunchifyList . iterator ( ) ;
         while ( crunchifyIterator . hasNext ( ) ) {
             System . out . println ( crunchifyIterator . next ( ) ) ;
         }
 
         // ListIterator - traverse a list of elements in either forward or backward order
         // An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration,
         // and obtain the iterator's current position in the list.
         System . out . println ( "\n==============> 4. ListIterator Example..." ) ;
         ListIterator <String> crunchifyListIterator = crunchifyList . listIterator ( ) ;
         while ( crunchifyListIterator . hasNext ( ) ) {
             System . out . println ( crunchifyListIterator . next ( ) ) ;
         }
 
         // while loop
         System . out . println ( "\n==============> 5. While Loop Example...." ) ;
         int i = 0 ;
         while ( i < crunchifyList . size ( ) ) {
             System . out . println ( crunchifyList . get ( i ) ) ;
             i ++ ;
         }
 
         // Iterable.forEach() util: Returns a sequential Stream with this collection as its source
         System . out . println ( "\n==============> 6. Iterable.forEach() Example...." ) ;
         crunchifyList . forEach ( ( temp ) - > {
             System . out . println ( temp ) ;
         } ) ;
 
         // collection Stream.forEach() util: Returns a sequential Stream with this collection as its source
         System . out . println ( "\n==============> 7. Stream.forEach() Example...." ) ;
         crunchifyList . stream ( ) . forEach ( ( crunchifyTemp ) - > System . out . println ( crunchifyTemp ) ) ;
     }
}

出力：

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============== > 1. Simple For loop Example .
Facebook
Paypal
Google
Yahoo
 
============== > 2. New Enhanced For loop Example . .
Facebook
Paypal
Google
Yahoo
 
============== > 3. Iterator Example . . .
Facebook
Paypal
Google
Yahoo
 
============== > 4. ListIterator Example . . .
Facebook
Paypal
Google
Yahoo
 
============== > 5. While Loop Example . . . .
Facebook
Paypal
Google
Yahoo
 
============== > 6. Iterable . forEach ( ) Example . . . .
Facebook
Paypal
Google
Yahoo
 
============== > 7. Stream . forEach ( ) Example . . . .
Facebook
Paypal
Google
Yahoo
 
Process finished with exit code 0