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A NullPointerException is an exception thrown by the Java Virtual Machine when you try to access a variable as if it were an object when it is contains null. For example, the following code would throw a NullPointerException:
String s;
if (s.charAt(0) == 'c') // this line throws NullPointerException
return "s[0] is 'c'";
What else can I help you with?
Can NullPointerException be used with ArithmaticException using throws keyword in java?
No. You cannot throw or catch Null pointer exceptions
How overcome problem of NullPointerException?
A NullPointerException is thrown when you attempt to access an object reference which is null. Example: String str = null; str.equals("x"); // <- NullPointerException To fix it, you must read the error message and find out what object is null. Determining how to ensure that this object is not set to null in the future must be made on a case-by-case basis.
What are the errors in this code?
the code is: function pppf($var1) { // Get PPPF Code Infomation $sql = "SELECT * FROM pppf_code"; $pppf_query = mysql_query($sql); while($pppf = mysql_fetch_assoc($pppf_query)) { $y = mysql_num_rows($pppf_query); if ($x<=$y) { $pppf_i = $pppf['input_text']; $pppf_o = $pppf['output_text']; $pppf_input = array($pppf_input.", '$pppf_i'"); $pppf_output = array($pppf_output.", '$pppf_o'"); } } echo $pppf_input['0']." | ".$pppf_output['0']."<br>"; $pppf_out = str_replace($pppf_input, $pppf_output, $var1); echo $pppf_out; }
Does exception always signal an error?
It depends on exactly how you define an error. If an exception is thrown, then it means something has gone wrong. Some Exceptions, such as a NullPointerException, will almost certainly signal an error in your code or data. Others, such as IOExceptions, can be caused by things outside your control, and would probably not be considered errors.
What are Class Constructor and Primitive data types?
class constructor is a function which has the same name as the class name and has no return type. primitive data types are the fundamental data types which are independent. eg:int,char,float etc..............
How do you overcome problem of NullPointerException?
By making sure that we do a null check everytime before using reference variables.
Can NullPointerException be used with ArithmaticException using throws keyword in java?
No. You cannot throw or catch Null pointer exceptions
What do you mean by NullPointer Exception?
NullPointerException - Is Thrown when attempting to access an object with a reference variable whose current value is null.
Throws statement in java?
throw new Throwable(); or throw new Error("Danger will Robinson!"); or throw new NullPointerException(); etc.
How overcome problem of NullPointerException?
A NullPointerException is thrown when you attempt to access an object reference which is null. Example: String str = null; str.equals("x"); // <- NullPointerException To fix it, you must read the error message and find out what object is null. Determining how to ensure that this object is not set to null in the future must be made on a case-by-case basis.
What are the errors in this code?
the code is: function pppf($var1) { // Get PPPF Code Infomation $sql = "SELECT * FROM pppf_code"; $pppf_query = mysql_query($sql); while($pppf = mysql_fetch_assoc($pppf_query)) { $y = mysql_num_rows($pppf_query); if ($x<=$y) { $pppf_i = $pppf['input_text']; $pppf_o = $pppf['output_text']; $pppf_input = array($pppf_input.", '$pppf_i'"); $pppf_output = array($pppf_output.", '$pppf_o'"); } } echo $pppf_input['0']." | ".$pppf_output['0']."<br>"; $pppf_out = str_replace($pppf_input, $pppf_output, $var1); echo $pppf_out; }
Does exception always signal an error?
It depends on exactly how you define an error. If an exception is thrown, then it means something has gone wrong. Some Exceptions, such as a NullPointerException, will almost certainly signal an error in your code or data. Others, such as IOExceptions, can be caused by things outside your control, and would probably not be considered errors.
Difference between checked and unchecked exception?
Checked exceptions are exceptions which need to be handled explicitly. These are the ones which require a try-catchblock or a throws keyword.Unchecked exceptions are exceptions which have no obligation to be handled. A NullPointerException is one common example.
What is exception and list some of the common type of exception?
Exceptions are thrown when Java encounters an error. They are a fundamental part of the Java error handling system. In a nutshell, Java will throw an Exception when it encounters an error so that an exception handler can "handle" the error. For instance, if a calculator program is given the command "1/0", Java can throw an ArithmeticException which could be reported back to the user.Some common types are:ArithmeticException - thrown when arithmetic error has occurred, like dividing by 0IOException - thrown when an input or output error has occurred, like a file not foundArrayIndexOutOfBoundsException - thrown when a nonexistent element of an array is requested, like arr[-1]NullPointerException - thrown when some operation if performed on an object whose value is nll.
What are Class Constructor and Primitive data types?
class constructor is a function which has the same name as the class name and has no return type. primitive data types are the fundamental data types which are independent. eg:int,char,float etc..............
What do you mean by null pointers?
A pointer is a memory address that points to a specific piece of data or object, depending on the features of the language one is speaking about. A null value is a concept that represents an abstract type of data meaning "no data" or "unknown data," and is distinct from values such as 0, or "", which is data that is known to be "nothing."A null pointer, then, is a pointer which has no data, meaning it has not been initialized to any specific value, and therefore unknown. In some languages, null pointers will cause exceptions, such as a NullPointerException, that can be handled by "error handling" mechanisms, while in other languages, access may be allowed to that pointer, potentially accessing system information or invalid memory addresses, causing the application or system to crash as memory is corrupted.Modern operating systems have little chance of a system crash, but a null pointer exception that isn't handled will result in a General Protection Fault in Windows, and similar error conditions on other operating systems.
How can you initialize an array in Java?
If you refering to Object then String[] something=new String[2]; Here you have to remember that something only allocated space for 2 String object but it did not created them yet. By default Objects are intantiated to null so if you try to print the content of an array System.out.println(something[0]);//print null System.out.println(something[0].toLowerCase()); Throws NullPointerException Couple other ways to create Arrays In java String[] something=new String[]{"Me","You"}; String[] something={"Me", "You"};
