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Kā atkārtot sarakstu Java

Java valodā, Saraksts ir ir interfeiss Kolekcijas ietvars . Tas mums nodrošina pasūtītās objektu kolekcijas uzturēšanu. List interfeisa ieviešanas klases ir ArrayList, LinkedList, Stack , un Vektors . ArrayList un LinkedList tiek plaši izmantoti Java . Šajā sadaļā mēs uzzināsim kā atkārtot sarakstu Java . Visā šajā sadaļā mēs izmantosim ArrayList .

Java for Loop

  1. Pamata for Loop
  2. Uzlabota cilpai

Java iteratori

  1. Iterators
  2. ListIterator

Java katrai metodei

  1. Iterable.forEach()
  2. Stream.forEach()

Java for Loop

Pamata for Loop

Java cilpai ir visizplatītākā plūsmas kontroles cilpa iterācijai. For cilpa satur mainīgo, kas darbojas kā indeksa numurs. Tas tiek izpildīts, līdz viss saraksts netiek atkārtots.

kā pārvērst veselu skaitli virknē Java

Sintakse:

 for(initialization; condition; increment or decrement) { //body of the loop } 

IterateListExample1.java

 import java.util.*; public class IterateListExample1 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate list using for loop for (int i = 0; i <city.size(); i++) { prints the elements of list system.out.println(city.get(i)); } < pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <h3>Enhanced for Loop</h3> <p>It is similar to the basic for loop. It is compact, easy, and readable. It is widely used to perform traversal over the List. It is easy in comparison to basic for loop.</p> <p> <strong>Syntax:</strong> </p> <pre> for(data_type variable : array | collection) { //body of the loop } </pre> <p> <strong>IterateListExample2.java</strong> </p> <pre> import java.util.*; public class IterateListExample2 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iteration over List using enhanced for loop for (String cities : city) { //prints the elements of the List System.out.println(cities); } } } </pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <h2>Java Iterator</h2> <h3>Iterator</h3> <p> <a href="/iterator-java">Java provides an interface Iterator</a> to <strong>iterate</strong> over the Collections, such as List, Map, etc. It contains two key methods next() and hasNaxt() that allows us to perform an iteration over the List.</p> <p> <strong>next():</strong> The next() method perform the iteration in forward order. It returns the next element in the List. It throws <strong>NoSuchElementException</strong> if the iteration does not contain the next element in the List. This method may be called repeatedly to iterate through the list, or intermixed with calls to previous() to go back and forth.</p> <p> <strong>Syntax:</strong> </p> <pre> E next() </pre> <p> <strong>hasNext():</strong> The hasNext() method helps us to find the last element of the List. It checks if the List has the next element or not. If the hasNext() method gets the element during traversing in the forward direction, returns true, else returns false and terminate the execution.</p> <p> <strong>Syntax:</strong> </p> <pre> boolean hasNext() </pre> <p> <strong>IterateListExample3.java</strong> </p> <pre> import java.util.*; public class IterateListExample3 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using enhances for loop Iterator cityIterator = city.iterator(); //iterator over List using while loop while(cityIterator.hasNext()) { System.out.println(cityIterator.next()); } } } </pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <h3>ListIterator</h3> <p>The ListIterator is also an interface that belongs to java.util package. It extends <strong>Iterator</strong> interface. It allows us to iterate over the List either in forward or backward order. The forward iteration over the List provides the same mechanism, as used by the Iterator. We use the next() and hasNext() method of the Iterator interface to iterate over the List.</p> <p> <strong>IterateListExample4.java</strong> </p> <pre> import java.util.*; public class IterateListExample4 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using the ListIterator ListIterator listIterator = city.listIterator(); while(listIterator.hasNext()) { //prints the elements of the List System.out.println(listIterator.next()); } } } </pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <h2>Java forEach Method</h2> <h3>Iterable.forEach()</h3> <p>The Iterable interface provides forEach() method to iterate over the List. It is available since Java 8. It performs the specified action for each element until all elements have been processed or the action throws an exception. It also accepts Lambda expressions as a parameter.</p> <p> <strong>Syntax:</strong> </p> <pre> default void forEach(Consumer action) </pre> <p>The default implementation behaves like:</p> <pre> for (T t : this) action.accept(t); </pre> <p>It accepts <strong>action</strong> as a parameter that is <strong>non-interfering</strong> (means that the data source is not modified at all during the execution of the stream pipeline) action to perform on the elements. It throws <strong>NullPointerException</strong> if the specified action is null.</p> <p>The <strong>Consumer</strong> is a functional interface that can be used as the assignment target for a lambda expression or method reference. T is the type of input to the operation. It represents an operation that accepts a single input argument and returns no result.</p> <p> <strong>IterateListExample5.java</strong> </p> <pre> import java.util.*; public class IterateListExample5 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using forEach city.forEach(System.out::println); } } </pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <h3>Stream.forEach()</h3> <p>Java Stream interface allows us to convert the List values into a stream. With the help of Stream interface we can access operations like forEach(), map(), and filter().</p> <p> <strong>Syntax:</strong> </p> <pre> void forEach(Consumer action) </pre> <p>It accepts <strong>action</strong> as a parameter that is <strong>non-interfering</strong> (means that the data source is not modified at all during the execution of the stream pipeline) action to perform on the elements.</p> <p>The <strong>Consumer</strong> is a functional interface that can be used as the assignment target for a lambda expression or method reference. T is the type of input to the operation. It represents an operation that accepts a single input argument and returns no result.</p> <p> <strong>IterateListExample5.java</strong> </p> <pre> import java.util.*; public class IterateListExample5 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using forEach loop city.stream().forEach((c) -&gt; System.out.println(c)); } } </pre> <p> <strong>Output</strong> </p> <pre> Boston San Diego Las Vegas Houston Miami Austin </pre> <hr></city.size();>

Uzlabota cilpai

Tas ir līdzīgs pamata cilpai. Tas ir kompakts, viegli un lasāms. To plaši izmanto, lai veiktu šķērsošanu sarakstā. Tas ir viegli, salīdzinot ar pamata cilpu.

Sintakse:

 for(data_type variable : array | collection) { //body of the loop } 

IterateListExample2.java

 import java.util.*; public class IterateListExample2 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iteration over List using enhanced for loop for (String cities : city) { //prints the elements of the List System.out.println(cities); } } } 

Izvade

 Boston San Diego Las Vegas Houston Miami Austin 

Java iterators

Iterators

Java nodrošina interfeisa iteratoru uz atkārtojiet pār kolekcijām, piemēram, sarakstu, karti utt. Tajā ir divas galvenās metodes next() un hasNaxt(), kas ļauj mums veikt iterāciju sarakstā.

Nākamais(): Nākamā() metode veic iterāciju uz priekšu. Tas atgriež nākamo elementu sarakstā. Tas met NoSuchElementException ja iterācija nesatur nākamo elementu sarakstā. Šo metodi var izsaukt atkārtoti, lai atkārtotu sarakstu, vai sajaukt ar izsaukumiem uz previous(), lai dotos uz priekšu un atpakaļ.

Sintakse:

 E next() 

hasNext(): Metode hasNext() palīdz mums atrast pēdējo saraksta elementu. Tas pārbauda, ​​vai sarakstā ir nākamais elements. Ja metode hasNext() iegūst elementu pārvietošanās laikā uz priekšu, atgriež true, pretējā gadījumā atgriež false un pārtrauc izpildi.

kā pārvērst str par int

Sintakse:

 boolean hasNext() 

IterateListExample3.java

 import java.util.*; public class IterateListExample3 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using enhances for loop Iterator cityIterator = city.iterator(); //iterator over List using while loop while(cityIterator.hasNext()) { System.out.println(cityIterator.next()); } } } 

Izvade

 Boston San Diego Las Vegas Houston Miami Austin 

ListIterator

ListIterator ir arī saskarne, kas pieder pakotnei java.util. Tas pagarina Iterators saskarne. Tas ļauj mums atkārtot sarakstu uz priekšu vai atpakaļ secībā. Uz priekšu veiktā iterācija sarakstā nodrošina to pašu mehānismu, ko izmanto iterators. Mēs izmantojam Iterator saskarnes metodi next() un hasNext(), lai atkārtotu sarakstu.

IterateListExample4.java

 import java.util.*; public class IterateListExample4 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using the ListIterator ListIterator listIterator = city.listIterator(); while(listIterator.hasNext()) { //prints the elements of the List System.out.println(listIterator.next()); } } } 

Izvade

 Boston San Diego Las Vegas Houston Miami Austin 

Java katrai metodei

Iterable.forEach()

Iterējamais interfeiss nodrošina katras () metodes atkārtošanu sarakstā. Tas ir pieejams kopš Java 8. Tas veic norādīto darbību katram elementam, līdz visi elementi ir apstrādāti vai darbība rada izņēmumu. Tas arī pieņem Lambda izteiksmes kā parametru.

Sintakse:

 default void forEach(Consumer action) 

Noklusējuma ieviešana darbojas šādi:

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

Tā pieņem darbība kā parametrs, kas ir neiejaucas (nozīmē, ka datu avots straumes konveijera izpildes laikā vispār netiek modificēts) darbība, kas jāveic elementiem. Tas met NullPointerException ja norādītā darbība ir nulle.

The Patērētājs ir funkcionāls interfeiss, ko var izmantot kā lambda izteiksmes vai metodes atsauces piešķiršanas mērķi. T ir operācijas ievades veids. Tas apzīmē darbību, kas pieņem vienu ievades argumentu un neatgriež rezultātu.

IterateListExample5.java

 import java.util.*; public class IterateListExample5 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using forEach city.forEach(System.out::println); } } 

Izvade

 Boston San Diego Las Vegas Houston Miami Austin 

Stream.forEach()

Java Stream interfeiss ļauj mums pārvērst saraksta vērtības straumē. Ar Stream interfeisa palīdzību mēs varam piekļūt tādām darbībām kā forEach(), map() un filter().

Sintakse:

 void forEach(Consumer action) 

Tā pieņem darbība kā parametrs, kas ir neiejaucas (nozīmē, ka datu avots straumes konveijera izpildes laikā vispār netiek modificēts) darbība, kas jāveic elementiem.

The Patērētājs ir funkcionāls interfeiss, ko var izmantot kā lambda izteiksmes vai metodes atsauces piešķiršanas mērķi. T ir operācijas ievades veids. Tas apzīmē darbību, kas pieņem vienu ievades argumentu un neatgriež rezultātu.

js nomaiņa

IterateListExample5.java

 import java.util.*; public class IterateListExample5 { public static void main(String args[]) { //defining a List List city = Arrays.asList(&apos;Boston&apos;, &apos;San Diego&apos;, &apos;Las Vegas&apos;, &apos;Houston&apos;, &apos;Miami&apos;, &apos;Austin&apos;); //iterate List using forEach loop city.stream().forEach((c) -&gt; System.out.println(c)); } } 

Izvade

 Boston San Diego Las Vegas Houston Miami Austin