class One {

static int value = 1;

One getValue() {

return null;

}

public static void main(String args[])  {

One one = new One();

System.out.println(one.getValue().value);

}

}

It won’t throw a ‘NullPointerException’. The o/p will be 1. Think why

Scheduling tasks using Cron  – Part II

It is an event that disrupts the normal flow of program execution.

When an exception is thrown from inside a method, the Java Runtime System attempts to find an ordered list of methods that had been called to reach the method where the error occured. This list (of methods) is known as the Call Stack.

Please see the figure below:

Java Call Stack

The job of runtime system is to search the call stack for a method that contains a block of code that can handle the exception. This block of code is called exception handler. The runtime system start search with the method in which the error occured and proceeds through the call stack in the reverse order in which the methods were called.

The runtime system passes the exception to the appropriate handler when found one. An exception handler is considered appropriate if the type of exception object thrown matches the type that can be handled by the handler.

In Preemptive scheduling, the thread with the highest priority runs first. it keeps running until it reaches wait or dead stage or a higher priority thread comes.
In Time-sliced scheduling, the thread executes for a predefined slice of time.

The JVM basically uses Preemptive scheduling. All Java threads have a priority and the thread with he highest priority is scheduled to run by the JVM.

The Thread class contains three integer priority constants
1. MIN_PRIORITY [1]
2. NORM_PRIORITY [5]
3. MAX_PRIORITY [10]

The default thread priority is NORM_PRIORITY. To get and set a thread’s priority we have getPriority() and setPriority() respectively.

BUT WE CANNOT rely on thread priority as a guarantee that the highest priority thread will always be running; the operating system has the final say as actual Scheduling depends on the OS which can be Preemptive or Time-sliced.

In case two threads have the same priority,
- a FIFO ordering is followed if the Operating System (OS) uses Preemptive.
- Java quickly switches between them in round-robin fashion if the OS uses Time-slicing.

Thanx,
Sandeep.

1) first.jsp
it has the following statements
include file=”included.jsp”
page errorPage=”ErrorPage1.jsp”

2) include.jsp

page errorPage=”ErrorPage2.jsp”
Hello World

If we load first.jsp, it will throw an error. The reason is – we can’t have more than one occurrence of errorPage attribute with different values.
ie. first.jsp will have the second errorPage attribute with a different value when include.jsp is included.

thanx,
Sandeep

For primitive types, we don’t use the new keyword. Using new will place the objects in heap, which would be very costly for small and simple variables. Primotive types create variables that are stored on the stack.
new() and malloc() allocate memory from heap.
Heap size is found at the compile time which varies from computer to computer.
Stack size is found at the run time which does not vary.

thanx,
Sandeep.