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Как да разрешим IllegalStateException в Java?

Ан изключение е нежелана и неочаквана грешка в програмата. През повечето време изключение възниква, когато има грешка в нашия код, но тя може да бъде обработена. Това нарушава нормалния поток на кода.

Например, кодът хвърля изключение, ако потребителят е въвел невалидна информация, ако кодът не може да прочете файла, намиращ се на отдалечено място, или ако мрежовата връзка е изгубена по време на комуникацията.

IllegalStateException в Java

IllegalStateException е подкласът на класа RuntimeException и следователно е непроверено изключение. Повдига се изрично от програмиста или от разработчика на API. Той се хвърля, когато извикването на метод е незаконно или методът е извикан в неправилно време.

Например, след като стартираме нишка, не можем да рестартираме същата нишка отново; ако се опитаме да направим това, то хвърля изключение по време на изпълнение, т.е. IllegalStateException .

Изключението може възникват в кода обикновено, когато работим с рамката на колекциите. Списъкът, Опашката, Картите, Дървото са някои от колекциите. От тях List и Queues са склонни да хвърлят изключението за незаконно състояние при конкретните условия.

Забележка: Изключението IllegalStateException не е ограничено само до рамката на колекциите.

Нека да видим някои от сценария, където IllegalStateException ще бъдат хвърлени.

mb срещу gb

Пример 1:

Следващата програма на Java описва ситуацията, в която се опитваме да извикаме метода start(), когато методът run() вече се изпълнява.

IllegalStateExceptionTest1.java

 // importing necessary packages import java.io.*; import java.util.*; // creating a new thread in NewThread class by extending Thread class // below class is acts as a helper class class NewThread extends Thread { // declaring the run() method // executes 3 times using for loop public void run() { for (int i = 0; i <3; i++) { displaying the text system.out.println('this is example of illegalstateexception'); } creating main class public illegalstateexceptiontest1 method static void main(string[] args) object above helper newthread t="new" newthread(); starting created thread using start() t.start(); thread'); again when it already running this gives an exception < pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java.webp" alt="How to resolve IllegalStateException in Java"> <h3>Example 2:</h3> <p>The following code depicts the situation where we call the start() method on a thread when the execution of run() method is over.</p> <p> <strong>IllegalStateExceptionTest2.java</strong> </p> <pre> // importing necessary packages import java.io.*; import java.util.*; // creating a new thread in NewThread class by extending Thread class // below class is acts as a helper class class NewThread extends Thread { // declaring the run() method // executes 3 times using for loop public void run() { for (int i = 0; i <3; i++) { displaying the text system.out.println('this is example of illegalstateexception'); } creating main class public illegalstateexceptiontest2 method static void main(string[] args) object above helper newthread t="new" newthread(); starting created thread using start() t.start(); try system.out.println('main going to sleep'); putting on sleep for 4000ms t.sleep(4000); awaken'); catch (exception e) system.out.println(e); message thread'); calling over a dead this also gives an exception < pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-2.webp" alt="How to resolve IllegalStateException in Java"> <h3>Example 3:</h3> <p>The following code explains the situation where we are using the remove() method to remove the element from the ArrayList, before moving to the first element.</p> <p> <strong>IllegalStateExceptionTest3.java</strong> </p> <pre> // importing necessary packages import java.util.ArrayList; import java.util.ListIterator; // creating the main class public class IllegalStateExceptionTest3 { // main method public static void main(String args[]) { // instantiating the object of ArrayList ArrayList list = new ArrayList(); // adding elements to the ArrayList list.add(&apos;Nirnay&apos;); list.add(&apos;Anu&apos;); list.add(&apos;Swara&apos;); list.add(&apos;Pavan&apos;); // creating the iterator object to iterate the list ListIterator it = list.listIterator(); // removing the element without moving to first position // gives an exception it.remove(); } } </pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-3.webp" alt="How to resolve IllegalStateException in Java"> <h2>Solution for the IllegalStateException</h2> <p>To avoid the <strong>java.lang.IllegalStateException</strong> in Java we should take care that any method in our code cannot be called at inappropriate or illegal time.</p> <p> <strong>Solution for example 1 and 2:</strong> </p> <p>Consider the above example 1 and 2 where we have called the start() method more than once. If we call it only once, we will not get this exception. Because start() method is not called after starting the thread.</p> <p> <strong>IllegalStateExceptionSolution.java</strong> </p> <pre> // importing necessary packages import java.io.*; import java.util.*; // creating a new thread in NewThread class by extending Thread class // below class is acts as a helper class class NewThread extends Thread { // declaring the run() method // executes 3 times using for loop public void run() { for (int i = 0; i <3; i++) { displaying the text system.out.println('this is example of illegalstateexception'); } creating main class public illegalstateexceptionsolution method static void main(string[] args) object above helper newthread t="new" newthread(); starting created thread using start() t.start(); try system.out.println('main going to sleep'); putting on sleep for 4000ms t.sleep(4000); awaken'); catch (exception e) system.out.println(e); message thread'); we do not call again < pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-4.webp" alt="How to resolve IllegalStateException in Java"> <p> <strong>Solution for Example 3:</strong> </p> <p>The remove() method of the ArrayList class is used to remove the last element after calling the next() method.</p> <ul> <li>After removing element at current index we have to move next element to remove it. (for every call of the next() method, we have to invoke the remove() method only once).</li> <li>As the initial position of list will be before the first element, we cannot call the remove() method without calling the next() method.</li> </ul> <p>In order to prevent the exception we need to follow the above steps in our Java code.</p> <p> <strong>IllegalStateExceptionSolution2.java</strong> </p> <pre> // importing necessary packages import java.util.ArrayList; import java.util.ListIterator; // creating the main class public class IllegalStateExceptionSolution2 { // main method public static void main(String args[]) { // instantiating the object of ArrayList ArrayList list = new ArrayList(); // adding elements to the ArrayList list.add(&apos;Nirnay&apos;); list.add(&apos;Anu&apos;); list.add(&apos;Swara&apos;); list.add(&apos;Pavan&apos;); // creating the iterator object to iterate the list ListIterator it = list.listIterator(); // using the next() method before remove() it.next(); // removing the element without moving to first position it.remove(); // displaying new ArrayList System.out.println(&apos;List after removing the first element: &apos; + list); } } </pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-5.webp" alt="How to resolve IllegalStateException in Java"> <hr></3;></pre></3;></pre></3;>

Изход:

Как да разрешите IllegalStateException в Java

Решение за IllegalStateException

За да избегнете java.lang.IllegalStateException в Java трябва да внимаваме всеки метод в нашия код да не може да бъде извикан в неподходящо или незаконно време.

Решение за пример 1 и 2:

Помислете за горните примери 1 и 2, където сме извикали метода start() повече от веднъж. Ако го извикаме само веднъж, няма да получим това изключение. Тъй като методът start() не се извиква след стартиране на нишката.

IllegalStateExceptionSolution.java

 // importing necessary packages import java.io.*; import java.util.*; // creating a new thread in NewThread class by extending Thread class // below class is acts as a helper class class NewThread extends Thread { // declaring the run() method // executes 3 times using for loop public void run() { for (int i = 0; i <3; i++) { displaying the text system.out.println(\'this is example of illegalstateexception\'); } creating main class public illegalstateexceptionsolution method static void main(string[] args) object above helper newthread t="new" newthread(); starting created thread using start() t.start(); try system.out.println(\'main going to sleep\'); putting on sleep for 4000ms t.sleep(4000); awaken\'); catch (exception e) system.out.println(e); message thread\'); we do not call again < pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-4.webp" alt="How to resolve IllegalStateException in Java"> <p> <strong>Solution for Example 3:</strong> </p> <p>The remove() method of the ArrayList class is used to remove the last element after calling the next() method.</p> <ul> <li>After removing element at current index we have to move next element to remove it. (for every call of the next() method, we have to invoke the remove() method only once).</li> <li>As the initial position of list will be before the first element, we cannot call the remove() method without calling the next() method.</li> </ul> <p>In order to prevent the exception we need to follow the above steps in our Java code.</p> <p> <strong>IllegalStateExceptionSolution2.java</strong> </p> <pre> // importing necessary packages import java.util.ArrayList; import java.util.ListIterator; // creating the main class public class IllegalStateExceptionSolution2 { // main method public static void main(String args[]) { // instantiating the object of ArrayList ArrayList list = new ArrayList(); // adding elements to the ArrayList list.add(&apos;Nirnay&apos;); list.add(&apos;Anu&apos;); list.add(&apos;Swara&apos;); list.add(&apos;Pavan&apos;); // creating the iterator object to iterate the list ListIterator it = list.listIterator(); // using the next() method before remove() it.next(); // removing the element without moving to first position it.remove(); // displaying new ArrayList System.out.println(&apos;List after removing the first element: &apos; + list); } } </pre> <p> <strong>Output:</strong> </p> <img src="//techcodeview.com/img/java-tutorial/19/how-resolve-illegalstateexception-java-5.webp" alt="How to resolve IllegalStateException in Java"> <hr></3;>

Изход:

Как да разрешите IllegalStateException в Java