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Which object waits for and responds toan event from a GUI component?

irakobra [83]

Answer:

The answer is action eventlistener

Explanation:

It is an event handler and it is easy to implement.In java we call them even listeners it is function or a sub routine or a procedure that waits for an event to occur and respond to an event from a GUI component.

8 0

3 years ago

Consider the following general code for allowing access to a resource:

Margaret [11]

Answer:

a) The code allows access even when IsAccessAllowed(...) method fails.

b) Either use If

(dwRet = ACCESS_ALLOWED)

or use

if (dwRet == NO_ERROR)

to avoid flaw

Explanation:

Lets first see what the code chunk does:

DWORD dwRet = IsAccessAllowed(...);

if (dwRet == ERROR_ACCESS_DENIED) {

// Security check failed.

// Inform user that access is denied.

} else {

// Security check OK.

}

In the given code, DWORD is basically a data type for double word type integers and this is defined in windows.h

So there is DWORD type variable dwRet that is assigned a method calls.

The method is IsAccessAllowed() which checks if the access is allowed to user.

if (dwRet == ERROR_ACCESS_DENIED) condition basically checks if the value of DWORD type variable dwRet is equal to ERROR_ACCESS_DENIED

If this condition evaluates to true then the security checks fails and user is informed via some message or action that the access is denied. But when the if condition evaluates to false then the else part executes which allows access.

So basically this chunk of code checks if the error ERROR_ACCESS_DENIED is returned.

Now the flaw in this program is what if the method IsAccessAllowed() by any reason. The reasons can be system failure or the memory failure. In memory failure case for example, the system returns out of memory error. So this means that the error is not ERROR_ACCESS_DENIED. Instead it is out of memory error. So in such a case the user is allowed access as the if condition evaluates to false and else part executes. So if any other error is produced due to some reason like mentioned above, then user has unrestricted access.

This shows that the doe should not check for the failure or rely on checking ERROR_ACCESS_DENIED to allow access but instead it should check for success. Code should only give access privilege if access is allowed successfully or no error is produced.

So to avoid this flaw the code is altered as:

DWORD dwRet = IsAccessAllowed(...);

If (dwRet = ACCESS_ALLOWED) {

//Security check OK.

} else {

//Security check failed.

//Inform user that access is denied.

}

This will only allow access if ACCESS_ALLOWED evaluates to true and success is checked instead of failure here

You can also alter the if condition as:

If (dwRet = No_Error)

or

If (dwRet = 0)

The above if conditions checks if the access is allowed or if no error is produced. Only then it will allowed access otherwise not. So the access check is a success is checked first and failure (for any reason). The user is allowed access only if there is no error otherwise user is not allowed access.

6 0

3 years ago

This is going to get taken down but I dont care add me on discord cause ima bored<br> -Red-#9847

Alex777 [14]

Answer:

I WILL

Explanation:

6 0

2 years ago

There will be 10 numbers stored contiguously in the computer at location x 7000 . Write a complete LC-3 program, starting at loc

Artist 52 [7]

Answer:

The LC-3 (Little Computer 3) is an ISA definition for a 16-bit computer. Its architecture includes physical memory mapped I/O via a keyboard and display; TRAPs to the operating system for handling service calls; conditional branches on N, Z, and P condition codes; a subroutine call/return mechanism; a minimal set of operation instructions (ADD, AND, and NOT); and various addressing modes for loads and stores (direct, indirect, Base+offset, PC-relative, and an immediate mode for loading effective addresses). Programs written in LC-3 assembler execute out of a 65536 word memory space. All references to memory, from loading instructions to loading and storing register values, pass through the get Mem Adr() function. The hardware/software function of Project 5 is to translate virtual addresses to physical addresses in a restricted memory space. The following is the default, pass-through, MMU code for all memory references by the LC-3 simulator.

unsigned short int get Mem Adr(int va, int rwFlg)

{

unsigned short int pa;

// Warning: Use of system calls that can cause context switches may result in address translation failure

// You should only need to use gittid() once which has already been called for you below. No other syscalls

// are necessary.

TCB* tcb = get TCB();

int task RPT = tcb [gettid()].RPT;

pa = va;

// turn off virtual addressing for system RAM

if (va < 0x3000) return &memory[va];

return &memory[pa];

} // end get MemAdr

Simple OS, Tasks, and the LC-3 Simulator

We introduce into our simple-os a new task that is an lc3 Task. An lc3 Task is a running LC-3 simulator that executes an LC-3 program loaded into the LC-3 memory. The memory for the LC-3 simulator, however, is a single global array. This single global array for memory means that alllc3 Tasks created by the shell use the same memory for their programs. As all LC-3 programs start at address 0x3000 in LC-3, each task overwrites another tasks LC-3 program when the scheduler swaps task. The LC-3 simulator (lc3 Task) invokes the SWAP command every several LC-3 instruction cycles. This swap invocation means the scheduler is going to be swapping LC-3 tasks before the tasks actually complete execution so over writing another LC-3 task's memory in the LC-3 simulator is not a good thing.

You are going to implement virtual memory for the LC-3 simulator so up to 32 LC-3 tasks can be active in the LC-3 simulator memory without corrupting each others data. To implement the virtual memory, we have routed all accesses to LC-3 memory through a get Mem Adr function that is the MMU for the LC-3 simulator. In essence, we now have a single LC-3 simulator with a single unified global memory array yet we provide multi-tasking in the simulator for up to 32 LC-3 programs running in their own private address space using virtual memory.

We are implementing a two level page table for the virtual memory in this programming task. A two level table relies on referring to two page tables both indexed by separate page numbers to complete an address translation from a virtual to a physical address. The first table is referred to as the root page table or RPT for short. The root page table is a fixed static table that always resides in memory. There is exactly one RPT per LC-3 task. Always.

The memory layout for the LC=3 simulator including the system (kernel) area that is always resident and non-paged (i.e., no virtual address translation).

The two figures try to illustrate the situation. The lower figure below demonstrates the use of the two level page table. The RPT resident in non-virtual memory is first referenced to get the address of the second level user page table or (UPT) for short. The right figure in purple and green illustrates the memory layout more precisely. Anything below the address 0x3000 is considered non-virtual. The address space is not paged. The memory in the region 0x2400 through 0x3000 is reserved for the RPTs for up to thirty-two LC-3 tasks. These tables are again always present in memory and are not paged. Accessing any RPT does not require any type of address translation.

The addresses that reside above 0x3000 require an address translation. The memory area is in the virtual address space of the program. This virtual address space means that a UPT belonging to any given task is accessed using a virtual address. You must use the RPT in the system memory to keep track of the correct physical address for the UPT location. Once you have the physical address of the UPT you can complete the address translation by finding the data frame and combining it with the page offset to arrive at your final absolute physical address.

A Two-level page table for virtual memory management.

x7000 123F x7000 0042

x7001 6534 x7001 6534

x7002 300F x7002 300F

x7003 4005 after the program is run, memory x7003 4005

x7004 3F19

7 0

3 years ago

Read 2 more answers

Write a recursive function that prints out the items of a (possibly empty) singly linked list of integers in reverse order. The

MrRa [10]

Answer:

Follows are the method definition to this question:

void Reverse_Order(struct Node* h)//defining a recursive method Reverse_Order that takes structure in parameter

{

if (h == NULL)//use if block to check head equal to null

return;//use return keyword

Reverse_Order(h->next);//call method recursively

cout<<h->data;//print data

}

Explanation:

In the above code, a recursive method "Reverse_Order" takes structure as the parameter, and inside the method, structure variable h is used that uses the if conditional statement to check the header equal to null.

In the condition is true, it will use the return keyword, and in the next step, it calls the method recursively, and print its value in the reverse order.

8 0

3 years ago