If you attempt to dereference num before creating the object you get a NullPointerException. In the second line, the new keyword is used to instantiate (or create) an object of type Integer, and the reference variable num is assigned to that Integer object. Since you have not yet said what to point to, Java sets it to null. The first line declares a variable named num, but it does not actually contain a reference value yet. So you have a reference to something that does not actually exist. The NullPointerException (NPE) typically occurs when you declare a variable but did not create an object and assign it to the variable before trying to use the contents of the variable. If a reference variable is set to null either explicitly by you or through Java automatically, and you attempt to dereference it you get a NullPointerException. You can get a null value in a reference variable if you explicitly set it that way, or a reference variable is uninitialized and the compiler does not catch it (Java will automatically set the variable to null). Reference variables can be set to null which means " I am referencing nothing". Now here is where things get interesting. All primitives have to be initialized to a usable value before they are manipulated. These two lines will crash the program because no value is specified for x and we are trying to use x's value to specify y.
#Null pointer exception syncing supersync playlists code
For example variables of type Object are references.Ĭonsider the following code where you declare a variable of primitive type int and don't initialize it: int x By convention reference types are usually denoted with a type that starts in uppercase. to access a method or field, or using [ to index an array. If you want to manipulate the Object that a reference variable refers to you must dereference it. References: variables that contain the memory address of an Object i.e. For example variables of type int or char are primitives. By convention primitive types start with a lowercase letter. If you want to manipulate the data in a primitive variable you can manipulate that variable directly. Take a look at the below example: package are two overarching types of variables in Java: So if you must allow NullPointerException in some places in your code then make sure you make them more informative than they usually are. If a caller passes null in some parameter for which null values are prohibited, convention dictates that NullPointerException be thrown rather than IllegalArgumentException.” 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. What if we must allow NullPointerException in Some Places Please let me know if you know some more such language constructs which do not fail when null is encountered.ĥ. no NullPointerException because staticAttribute is static variable defined in class MyObject
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. If (StringUtils.isNotEmpty(obj.getvalue())) 4.2. Use the following methods for better handling the strings in your code. Use Apache Commons StringUtils for String OperationsĪpache Commons Lang is a collection of several utility classes for various kinds of operation. To prevent NullPointerException (NPE), use this operator like the below code: String str = (param = null) ? "NA" : param 3.2. It is more like an if-else construct but it is more effective and expressive. If the expression is evaluated as true then the entire expression returns value1 otherwise value2.
It has syntax like : boolean expression ? value1 : value2 Ternary operator results in the value on the left-hand side if not null else right-hand side is evaluated. Best Ways to Avoid NullPointerException 3.1. ( s.toString() ) // 's' is un-initialized and is nullģ. When we try to access it in the next statement s.toString(), we get the NullPointerException. In the given example, String s has been declared but not initialized. It essentially means that the object’s reference variable is not pointing anywhere and refers to nothing or ‘null’.
NullPointerException is a runtime condition where we try to access or modify an object which has not been initialized yet. Why NullPointerException Occur in the Code? What if we must allow NullPointerException in Some Placesġ. Discourage Passing of null as Method Arguments Use Apache Commons StringUtils for String Operations
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