Java has a fairly sophisticated garbage collection system, and in general you don't worry about memory leaks, as they only happen in a few very specific circumstances (notably, when adding listeners to Swing GUI objects and not removing them). If you need more sophistcated memory management, java provides the clases in the java.lang.ref package.
C is not an object-oriented language -- there are no destructors. In C++, however, an object's destructor is invoked automatically when the object falls from scope. The destructor can also be invoked by manually deleting a raw pointer to the object (or one of its base classes), however you should only ever use the delete operator if the object was instantiated with the new operator, and only after all references or pointers to the object have fallen from scope. The safest way to manage raw pointers is to use a resource handle or smart pointer.
Get and Post are two different ways of passing data from your web application screen and the servlet.When you submit your web page (form) the data would reach the servlet in either of the two ways Get and Post. The methods doGet() and doPost() are servlet specific action methods that can handle the submit actions. If you have specified your form submission type as Get then the doGet() would be invoked and if you have specified as Post the doPost() would be invoked.
Generally speaking, a handle is an abstract reference to a resource that is managed by another system, such as the operating system or a database. Normally we use pointers to reference objects in memory, but the objects we point at are under our direct control; they do not arbitrarily relocate themselves without us knowing about it. But resources outwith our direct control have a nasty habit of moving around in memory behind our backs, which would be disastrous if we simply pointed at them (our pointers would constantly be invalidated). By using a handle, the resources can freely move around as required by the external system that controls them without invalidating the handle. Implementations vary but a handle is often implemented as a key or index into a table of resources which map the handle to an actual memory address. Thus when we pass a handle into an API that understands the handle's purpose, the handle can be dereferenced accordingly. For instance, when we call various functions in the Windows Win32 API, we might pass an HWND value which is a handle to a specific window, or an HKEY value which is a handle to a specific registry key, or an HFILE which is a handle to a disk file. We use these same APIs to initialise the handles and, if required, release them when they are no longer required. We cannot predict where these objects will reside in memory at any given moment, but with a handle we don't have to because the system that controls those resources can use the handle to locate them for us, via the API provided by that system.
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