java.lang.nullpointerexception using datacrow

#JAVA.LANG.NULLPOINTEREXCEPTION USING DATACROW HOW TO#
#JAVA.LANG.NULLPOINTEREXCEPTION USING DATACROW CODE#

#JAVA.LANG.NULLPOINTEREXCEPTION USING DATACROW CODE#

The above code snippet will throw a NullPointerException. * The code here will not be reached, as an exception will be thrown. For example, observe the following case: String str = null Instead of invoking the method from the null object, consider invoking it from the literal.

The literal may be a String or the element of an Enum. 2.1 String comparison with literalsĪ very common case in an application’s execution code involves the comparison between a String variable and a literal. However, they do not eliminate the problem and the programmer should always be careful while coding an application. In the rest of this section, we will describe some techniques that deal with the aforementioned exception. Locate the method and the line where the exception was caught and then, figure out which reference equals to null in that specific line. The execution’s stack trace is provided by the JVM, in order to enable the debugging of the application. You must verify that the pointer is not null, before you request the method or a field from the object.Īlso, if the exception is thrown, use the information residing in the exception’s stack trace. Notice that, when you declare a reference variable, you are really creating a pointer to an object. In order to avoid the NullPointerException, ensure that all your objects are initialized properly, before you use them.

Notice the use of the null value that enables the unique instance creation.Ģ. That instance is initialized at most once inside the getInstance method. In this example, we declare a static instance of the Singleton class. ID = UUID.randomUUID().toString() // Create a random ID. * Make it private, in order to prevent the creation of new instances of 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.įor 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 The Null Object pattern provides an object as a surrogate for the lack of an object of a given type. It is extremely useful in coding some design patterns, such as Null Object pattern and Singleton pattern. Why do we need the null value?Īs already mentioned, null is a special value used in Java.

#JAVA.LANG.NULLPOINTEREXCEPTION USING DATACROW HOW TO#

Example – How to handle Java Null Pointer Exception 1.

Java.lang.nullpointerexception using datacrow