How to solve java.lang.nullpointerexception error

4 ответа 4

Когда вы объявляете переменную ссылочного типа, на самом деле вы создаете ссылку на объект данного типа. Рассмотрим следующий код для объявления переменной типа int:

В этом примере переменная x имеет тип int и Java инициализирует её как 0. Когда вы присвоите переменной значение 10 (вторая строка), это значение сохранится в ячейке памяти, на которую ссылается x .

Но когда вы объявляете ссылочный тип, процесс выглядит иначе. Посмотрим на следующий код:

В первой строке объявлена переменная num , ее тип не относится к встроенному, следовательно, значением является ссылка (тип этой переменной, Integer , является ссылочным типом). Поскольку вы еще не указали, на что собираетесь ссылаться, Java присвоит переменной значение Null , подразумевая «Я ни на что не ссылаюсь».

Во второй строке, ключевое слово new используется для создания объекта типа Integer . Этот объект имеет адрес в памяти, который присваивается переменной num . Теперь, с помощью переменной num вы можете обратиться к объекту используя оператора разыменования . .

Исключение, о котором вы говорите в вопросе, возникает, если вы объявили переменную, но не создали объект, то есть если вы попытаетесь разыменовать num до того, как создали объект, вы получите NullPointerException . В самом простом случае, компилятор обнаружит проблему и сообщит, что

Что говорит: «возможно, переменная num не инициализирована».

Иногда исключение вызвано именно тем, что объект действительно не был создан. К примеру, у вас может быть следующая функция:

В этом случае создание объекта (переменная num ) лежит на вызывающем коде, то есть вы предполагаете, что он был создан ранее – до вызова метода doSomething . К сожалению, следующий вызов метода вполне возможен:

В этом случае значение переменной num будет null . Лучшим способом избежать данного исключения будет проверка на равенство нулю. Как результат, функция doSomething должна быть переписана следующим образом:

Как альтернативный вариант предыдущему примеру вы можете сообщить вызывающему коду, что метод был вызван с неверными параметрами, например, с помощью IllegalArgumentException .

Conclusion

Remember that any NullPointerException comes about when you use a method on a variable which has not been initialized. Therefore, you can avoid the error by always setting a default value for every variable.

Other ways to avoid exception in thread main java.lang.nullpointerexception include using String.valueOf () method as opposed to toString () method. For instance, if an application code needs a string representation, use the static method instead of the toString method which throws an NPE.

Consider using the ternary operator which is in the form of Boolean expression seven value1: value2. Alternatively, you can avoid the error by creating methods which return to an empty collection, rather than those which return to null. Lastly, use Apache`s StringUtils class. Apache is a library which provides utilities for APU; for example, string manipulation methods.

Now that we have discussed what the error is, how it comes about, remedies to fix, and how to avoid it, you are in a better position to enjoy coding using Java.

What if we must allow NullPointerException in Some Places

Joshua bloch in effective java says that “Arguably, all erroneous method invocations boil down to an illegal argument or illegal state, but other exceptions are standardly used for certain kinds of illegal arguments and states. If a caller passes null in some parameter for which null values are prohibited, convention dictates that be thrown rather than .”

So if you must allow in some places in your code then make sure you make them more informative than they usually are.

Take a look at the below example:

Output of both method calls is this:

Clearly, the second stack trace is more informative and makes debugging easy. Use this in the future.

I am done with my experience around NullPointerException. If you know other points around the topic, please share with all of us !!

Happy Learning !!

Existing NullPointerException safe methods

3.1 Accessing static members or methods of a class

When your code attempts to access a static variable or method of a class, even if the object’s reference equals to , the JVM does not throw a . This is due to the fact that the Java compiler stores the static methods and fields in a special place, during the compilation procedure. Thus, the static fields and methods are not associated with objects, rather with the name of the class.

For example, the following code does not throw a :TestStatic.java:

class SampleClass {
 
     public static void printMessage() {
          System.out.println("Hello from Java Code Geeks!");
     }
}
 
public class TestStatic {
     public static void main(String[] args) {
          SampleClass sc = null;
          sc.printMessage();
     }
}

Notice, that despite the fact that the instance of the  equals to , the method will be executed properly. However, when it comes to static methods or fields, it is better to access them in a static way, such as .

3.2 The instanceof operator

The  operator can be used, even if the object’s reference equals to . The  operator returns false when the reference equals to null and does not throw a . For example, consider the following code snippet:

String str = null;
if(str instanceof String)
     System.out.println("It's an instance of the String class!");
else
     System.out.println("Not an instance of the String class!");

The result of the execution is, as expected:

Not an instance of the String class!

This was a tutorial on how to handle the Java Null Pointer Exception ( java.lang.NullPointerException –  )

Important points on NullPointerException in Java

1) NullPointerException is an unchecked exception because it extends RuntimeException and it doesn’t mandate try-catch block to handle it.

2) When you get NullPointerException to look at the line number to find out which object is null, it may be an object which is calling any method.

3) Modern IDE like Netbeans and Eclipse gives you the hyperlink of the line where NullPointerException occurs

4) You can set anException break point in Eclipse to suspend execution when NullPointerException occurs read 10 tips on java debugging in Eclipse for more details.

5) Don’t forget to see the name of Threadon which NullPointerException occurs. in multi-threading, NPE can be a little tricky if some random thread is setting a reference to null.

6) It’s best to avoid NullPointerException while coding by following some coding best practices or putting a null check on the database as a constraint.

That’s all on What is java.lang.NullPointerException, When it comes, and how to solve it. In the next part of this tutorial, we will look at some best java coding practices to avoid NullPointerException in Java.

Other Java debugging tutorial

Прекращена работа программы Java(TM) Platform SE binary

• Появление ошибки после первого запуска приложения свидетельствует о возможном отсутствии модуля Джава на ПК. Даже если есть какие-то следы ПО, то их лучше удалить и скачать плагин заново.
• Если Джава установлена на компьютере, сравните ее разрядность с аналогичным параметром операционной системы. Для этого найдите плагин в панели управления. Название, не содержащее цифр, говорит о версии x64, в противном случае установлена x32.

После исключения отсутствия модуля или несовместимости остается только один источник проблемы – видеокарта. Выполните следующие действия:

1. Создайте новую переменную среды. О том, как это сделать, рассказано выше. Напишите следующие параметры: имя – _JAVA_OPTIONS, значение – -Xmx256M.
2. Сохраните переменную, перейдите к настройкам в игре.
3. Отключите следующие параметры: VSync, VBos, Smooth Lighting.
4. FOV должно иметь значение Normal.

Для закрепления результата обновите драйвера для видеокарты и перезагрузите компьютер.

ява.ланг.Исключение NullPointerException-одно из самых популярных исключений в программировании на Java. Любой, кто работает на java, должен был видеть, как это появляется из ниоткуда в автономной программе java, а также в веб-приложении java .

Исключение NullPointerException является исключением во время выполнения, поэтому нам не нужно перехватывать его в программе. Исключение NullPointerException возникает в приложении, когда мы пытаемся выполнить какую-либо операцию над null , где требуется объект. Некоторые из распространенных причин исключения NullPointerException в программах Java являются:

1. Вызов метода в экземпляре объекта, но во время выполнения объект равен нулю.
2. Доступ к переменным экземпляра объекта, который является нулевым во время выполнения.
3. Выбрасывание null в программе
4. Доступ к индексу или изменение значения индекса массива, который равен нулю
5. Проверка длины массива, который является нулевым во время выполнения.

How to Fix the Exception in thread main java.lang.nullpointerexception java Error

To successfully solve a NullPointerException error in Java, you first need to identify the cause. It is quite easy to know the cause of the error. Just check the stack-trace of the exception. The stack-case will show you the exact line where the NPE has occurred.

Now, go to the line with the error and check for possible object operations. For instance, check an accessing field, throwing an exception, or calling methods. These will give you a hint on the null object.

After identifying the null object, we are halfway done. Understand why the object is invalid, and use the fixes below to solve the exception. Note that the second part of identifying the error may vary. The null may be from a factory or a thread.

Since there are different causes of the thread “main”java.lang.nullpointerexception, we cannot narrow down to one solution. However, these different fixes will help you avoid the error:

1st Fix: Hash Tables

Check your coding practice. If you are coding using a “Hash Table” class, a user from DevShed forums recommends the following:

1. Instead of using HashTable, it’s better to use HashMap since the former is really old.
2. Use a file with “Properties file format.”

Video Overview: Data Structures: Hash Tables

https://youtube.com/watch?v=shs0KM3wKv8%3F

2nd Fix: Cryptography Extension Update

According to Symantec, if you encounter the problem when trying to run Java LiveUpdate ConfigEditor, it could be that the JCE- Java Cryptography Extension files need to be updated, or that the LiveUpdate Configuration file is unreadable. You can fix this by following these steps:

1. Update your JCE policy files
2. Delete LiveUpdate.conf files then create a new one
3. Alternatively, you can also correct the Java Path

Note that this fix is only applicable to Windows 2003 and 2008.

Video Overview: Java Cryptography Architecture (JCA)

https://youtube.com/watch?v=OOMle0wnLZ8%3F

3rd Fix: Argument Method

Java Code Geeks recommend checking the argument of a method. Before performing the body of a method, it is essential to check the argument of the process for any null values. Only proceed with the execution after making sure there aren’t any null values.

Alternatively, you can send an “IllegalArguementException” and let the calling method know that something is wrong with previously passed arguments.

For instance:

public static int getLength(String s) {

if (s == null)

throw new IllegalArguementException (“The argument cannot be null”);

return s. length ( ) ;

}

Java Lang Nullpointerexception Hatası Nedenleri

NullPointerException bir çalışma zamanı istisnasıdır, bu yüzden onu programda yakalamamıza gerek yoktur. NullPointerException,  bir nesnenin gerekli olduğu yerlerde null üzerinde bazı işlemler yapmaya çalıştığımızda bir uygulamada ortaya çıkar. Java programlarında NullPointerException’ın yaygın nedenlerinden bazıları şunlardır:

1. Bir nesne örneğinde bir yöntemi çağırmak, ancak çalışma zamanında nesne boştur.
2. Çalışma zamanında boş olan bir nesne örneğinin değişkenlerine erişim.
3. Programda boş bırakma
4. Boş olan bir dizinin dizinine erişme veya dizinin değerini değiştirme
5. Çalışma zamanında boş olan bir dizinin uzunluğunu kontrol etme.

Как исправить ошибку java.lang.nullpointerexception

Как избавиться от ошибки java.lang.nullpointerexception? Способы борьбы с проблемой можно разделить на две основные группы – для пользователей и для разработчиков.

Для пользователей

Если вы встретились с данной ошибкой во время запуска (или работы) какой-либо программы (особенно это касается java.lang.nullpointerexception minecraft), то рекомендую выполнить следующее:

1. Переустановите пакет Java на своём компьютере. Скачать пакет можно, к примеру, вот отсюда;
2. Переустановите саму проблемную программу (или удалите проблемное обновление, если ошибка начала появляться после такового);
3. Напишите письмо в техническую поддержку программы (или ресурса) с подробным описанием проблемы и ждите ответа, возможно, разработчики скоро пофиксят баг.
4. Также, в случае проблем в работе игры Майнкрафт, некоторым пользователям помогло создание новой учётной записи с административными правами, и запуск игры от её имени.

Java ошибка в Майнкрафт

Для разработчиков

Разработчикам стоит обратить внимание на следующее:

1. Вызывайте методы equals(), а также equalsIgnoreCase() в известной строке литерала, и избегайте вызова данных методов у неизвестного объекта;
2. Вместо toString() используйте valueOf() в ситуации, когда результат равнозначен;
3. Применяйте null-безопасные библиотеки и методы;
4. Старайтесь избегать возвращения null из метода, лучше возвращайте пустую коллекцию;
5. Применяйте аннотации @Nullable и @NotNull;
6. Не нужно лишней автоупаковки и автораспаковки в создаваемом вами коде, что приводит к созданию ненужных временных объектов;
7. Регламентируйте границы на уровне СУБД;
8. Правильно объявляйте соглашения о кодировании и выполняйте их.

Ошибка может возникать на Windows XP, из-за отсутствия нужных библиотек для Java.

Необходимо установить на компьютер Microsoft Visual C++ 2010 Redistributable Package. Ссылка для скачивания: https://www.microsoft.com/ru-RU/download/details.aspx? >

Если Ваша проблема остаётся актуальной, запросите поддержку у TLauncher:

Создаю приложение с Яндекс.Картами. При переходе на активность с определением местоположения у меня выскакивает эта ошибка. Помогите. Вот код активности, куда указывает эта ошибка:

NullPointerException Safe Operations

4.1. instanceof Operator

The instanceof operator is NPE safe. So, always returns .

This operator does not cause a NullPointerException. You can eliminate messy conditional code if you remember this fact.

4.2. Accessing static Members of a Class

If you are dealing with static variables or static methods then you won’t get a null pointer exception even if you have your reference variable pointing to null because static variables and method calls are bonded during compile time based on the class name and not associated with the object.

Please let me know if you know some more such language constructs which do not fail when null is encountered.

How to Fix java.lang.NullPointerException Error

Creating a Null Pointer Exception is easy, but avoiding or fixing it is tricky. While some integrated development environments (IDEs) warn you if you are accessing a variable before initializing it with some compatible value, most IDEs can not figure this out in complex situations, such as when passing a variable through multiple method calls. The exact fix for a Null Pointer Exception depends upon your situation and code. Here are some of the top ways to fix common Null Pointer scenarios:

Check Your Code For Manual Errors

The biggest reason why Null Pointer Exceptions occur is human error. Make sure the program you have written carries the correct logic that you had initially intended. Also, run your eyes through the source code to check if you have missed out any statements, or misspelled any variables which may have led to some variable not being assigned a value.

Ensure that you have written your code the way your logic directs you to, and you have not missed out on writing any statements, or have not assigned objects to wrong references. As a rule of thumb, check that before any variable is used, it is initialized with an object.

Put Safety Checks Around Code That May Cause Null Pointer Exception

If you know the line of code that is causing your NullPointer and believe your logic is correct as well, you can wrap the section of code in a try-catch block, and define the behavior for when a Null Pointer is caught. This is how such a set-up will look like:

... // Some code above  try {   // Put the exception-prone code here } catch (NullPointerException npe) {   // Define what needs to be done when an NPE is caught }  // Some code below ...

This happens in situations where a certain reference variable may or may not contain null. More often than not, remote API responses, device interface responses are prone to this scenario. Depending upon the availability of a result or hardware, the response variable may or may not point to an instantiated object. Using safety checks is best-suited to handle these situations.

Check For Null Before Accessing Something

This method is similar to the try-catch method. In this method, an ‘if’ block is used to check for null values before accessing a variable. Here’s how the previous snippet of code would look like if an ‘if’ block is used to catch the error:

... // Some code above  If (myVar !== null ) {   // Put the success logic here } else {   // Handle null value here }  // Some code below ...

The biggest difference between the two methods is the scope of checks that they do. The if method checks the myVar variable only for null values, while the try-catch block catches any and all variables that are null.

This makes the ‘if’ block a more targeted and clean approach to accommodating null pointers in your application logic. However, if there is more than one variable that may be null, it is better to go with a try-catch block for simplicity.

How to solve NullPointerException in Java

To solve a NullPointerException in Java first we need to find the cause, which is very easy just look at the stack-trace of NullPointerException and it will show the exact line number where NPE has occurred. 
Now go to that line and look for possible object operations like accessing the field, calling method or throwing exception etc, that will give you an idea of which object is null. Now once you found that which object is null job is half done, now find out why that object is null and solve the java.lang.NullPointerException. 
This second part always very sometimes you get null object from the factory or sometimes some other thread might have set it null, though using Assertion in early phase of development you can minimize the chances of java.lang.NullPointerException but as I said its little bit related to the environment and can come on production even if tested fine in test environment.
It’s best to avoid NullPointerException by applying careful or defensive coding techniques and null-safe API methods.

What is java.lang.NullPointerException?

The Null Pointer Exception is one of the several Exceptions supported by the Java language. This indicates that an attempt has been made to access a reference variable that currently points to null.

Null is the default value in Java assigned to the variables which are not initialized by the user after or with a declaration. Consider the following example where you declare a variable like this:

String str;

And then try to print the contents of the variable:

System.out.println(str); // => null

As can be seen above, ‘null’ gets printed on the output. This shows that since the variable str is uninitialized, it currently points to, or holds the value, null. The issue that a null pointing variable poses is that the variable is only a reference, and it does not point to anything. If you try to carry out some operations on the data stored in a null pointing variable, the system will not know what to do. This happens because there is no data actually stored in the variable; it points to a void entity.

Example of java.lang.NullPointer.Exception

Looking for examples of java.lang.NullPointerException is not a difficult task, as all you need to do is not initialize a variable before trying to access it. For instance, let’s consider the StringBuilder class. StringBuilder is a class that is used to handle the formation and manipulation of strings. Here’s how you would normally use the class to create strings:

import java.util.StringBuilder;  public class Test {   public static void main(String[] args) {     StringBuilder sb = new StringBuilder();      sb.append("Hello ");     sb.append("World!");         String result = sb.toString();      System.out.println(result);     // => Hello World!   } }

If you run the above snippet, it will work just fine. Let’s take a look at its modified version that will throw a null pointer exception:

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import java.util.StringBuilder;  public class Test {   public static void main(String[] args) {     StringBuilder sb;      sb.append("Hello ");     sb.append("World!");         String result = sb.toString();      System.out.println(result);   } }

As you can see, we did not initialize an instance of the StringBuilder class while declaring it. When the lines are executed, sb does not point to any object in reality, rather it points to null. This is where a NullPointerException gets thrown. Due to the exception being thrown, the JVM cannot execute any statements after this.

Why do we need the null value?

As already mentioned,  is a special value used in Java. It is extremely useful in coding some design patterns, such as Null Object pattern and Singleton pattern. The Null Object pattern provides an object as a surrogate for the lack of an object of a given type. The Singleton pattern ensures that only one instance of a class is created and also, aims for providing a global point of access to the object.

For example, a sample way to create at most one instance of a class is to declare all its constructors as private and then, create a public method that returns the unique instance of the class:

TestSingleton.java

import java.util.UUID;
 
class Singleton {
 
     private static Singleton single = null;
     private String ID = null;
 
     private Singleton() {
          /* Make it private, in order to prevent the creation of new instances of
           * the Singleton class. */
 
          ID = UUID.randomUUID().toString(); // Create a random ID.
     }
 
     public static Singleton getInstance() {
          if (single == null)
               single = new Singleton();
 
          return single;
     }
 
     public String getID() {
          return this.ID;
     }
}
 
public class TestSingleton {
     public static void main(String[] args) {
          Singleton s = Singleton.getInstance();
          System.out.println(s.getID());
     }
}

In this example, we declare a static instance of the Singleton class. That instance is initialized at most once inside the  method. Notice the use of the  value that enables the unique instance creation.

Best Ways to Avoid NullPointerException

3.1. Use Ternary Operator

Ternary operator results in the value on the left-hand side if not null else right-hand side is evaluated. It has syntax like :

If the expression is evaluated as true then the entire expression returns value1 otherwise value2.

It is more like an if-else construct but it is more effective and expressive. To prevent NullPointerException (NPE), use this operator like the below code:

3.2. Use Apache Commons StringUtils for String Operations

Apache Commons Lang is a collection of several utility classes for various kinds of operation. One of them is StringUtils.java.

Use the following methods for better handling the strings in your code.

• StringUtils.isNotEmpty()
• StringUtils. IsEmpty()
• StringUtils.equals()

3.3. Fail Fast Method Arguments

We should always do the method input validation at the beginning of the method so that the rest of the code does not have to deal with the possibility of incorrect input.

Therefore if someone passes in a null as the method argument, things will break early in the execution lifecycle rather than in some deeper location where the root problem will be rather difficult to identify.

Aiming for fail-fast behavior is a good choice in most situations.

3.4. Consider Primitives instead of Objects

A null problem occurs where object references point to nothing. So it is always safe to use primitives. Consider using primitives as necessary because they do not suffer from null references.

All primitives have some default value assigned to them so be careful.

3.5. Carefully Consider Chained Method Calls

While chained statements are nice to look at in the code, they are not NPE friendly.

A single statement spread over several lines will give you the line number of the first line in the stack trace regardless of where it occurs.

These kind of chained statement will print only “NullPointerException occurred in line number xyz”. It really is hard to debug such code. Avoid such calls if possible.

3.6. Use valueOf() in place of toString()

If we have to print the string representation of any object, then consider not using toString() method. This is a very soft target for NPE.

Instead use String.valueOf(object). Even if the object is null in this case, it will not give an exception and will print ‘‘ to the output stream.

3.7. Avoid Returning null from Methods

An awesome tip to avoid NPE is to return empty strings or empty collections rather than null. Java 8 Optionals are a great alternative here.

Do this consistently across your application. You will note that a bucket load of null checks becomes unneeded if you do so.

Users of the above method, even if they missed the null check, will not see the ugly NPE.

3.8. Discourage Passing of null as Method Arguments

I have seen some method declarations where the method expects two or more parameters. If one parameter is passed as null, then also method works in a different manner. Avoid this.

Instead, we should define two methods; one with a single parameter and the second with two parameters.

Make parameters passing mandatory. This helps a lot when writing application logic inside methods because you are sure that method parameters will not be null; so you don’t put unnecessary assumptions and assertions.

3.9. Call equals() on ‘Safe’ Non-null Stringd

Instead of writing the below code for string comparison

write the above code like given below example. This will not cause in NPE even if param is passed as null.

How to fix NullPointerException

java.lang.NullPointerException is an unchecked exception, so we don’t have to catch it. The null pointer exceptions can be prevented using null checks and preventive coding techniques. Look at below code examples showing how to avoid .

if(mutex ==null) mutex =""; //preventive coding
		
synchronized(mutex) {
	System.out.println("synchronized block");
}

//using null checks
if(user!=null && user.getUserName() !=null) {
System.out.println("User Name: "+user.getUserName().toLowerCase());
}
if(user!=null && user.getUserName() !=null) {
	System.out.println("User ID: "+user.getUserId().toLowerCase());
}

When in Java Code NullPointerException doesn’t come

1) When you access any static method or static variable with null reference.

If you are dealing with static variables or static methods then you won’t get a null pointer exception even if you have your reference variable pointing to null because static variables and method calls are bonded during compile time based on the class name and not associated with an object. for example below code will run fine and not throw NullPointerException because «market» is an static variable inside Trade Class.

Trade lowBetaTrade = null;String market = lowBetaTrade.market; //no NullPointerException market is static variable