New data gets added to the end of the queue in Java

Generating QR Code JIS X 0510 in Java New data gets added to the end of the queue

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Like a stack, a queue can expand and shrink automatically, depending on the amount of data you store in it Unlike a stack that only lets you store and retrieve data from the top, a queue lets you store data on one end but remove that data from the opposite end Most programming languages don t offer the queue data structure as a built-in feature Instead, you have to create a queue with other data structures, such as an array or a linked list, to create an abstract data structure Fortunately, many programming language compilers come with libraries (or classes in object-oriented languages) of subprograms that have created the queue data structure for you Because a queue is just a data structure, you can declare a variable to represent a queue in Visual BasicNET by doing the following:

This command simply identifies a LongLine variable as a queue data structure The New command tells the computer to create a new stack

New data always gets stored at the end of the queue: When you first create a queue, it contains zero items Each time you add a new chunk of data to a queue, the queue expands automatically The front of the queue always contains the first or oldest data Like a collection or a dictionary, a queue can hold different data, such as both numbers and strings To add data to a queue, Visual BasicNET uses the Enqueue command along with the queue name like this:

Dim LongLine as New Queue LongLineEnqueue ( Tasha Korat )

This command stores the string Tasha Korat as the first item in the queue Each time you add another chunk of data to this queue, the new data gets tacked on to the end, which pushes the oldest data to the front of the queue If you added the string Tasha Korat, the number 725, and the string Gray, the stack would look like Figure 4-5

Dim LongLine as New Queue LongLineEnqueue ( Tasha Korat ) LongLineEnqueue (725) LongLineEnqueue ( Gray )

Figure 4-5: 725 The oldest data appears at the front Gray while the newest data appears at the end of the queue

You always remove data from a queue by taking that data off the front of the queue The front of the queue always contains the data that s been stored in the queue the longest In Visual BasicNET, you can remove and retrieve data off a queue by using the Dequeue command, as shown in the following Visual BasicNET example:

Dim LongLine as New Queue Dim X as Object LongLineEnqueue ( My cat ) LongLineEnqueue (10875) LongLineEnqueue ( Fat dog ) X = LongLineDequeue

As an alternative to removing data from a queue, you can retrieve data by using the Peek command To use the Peek command, you have to assign the value of the Peek command to a variable like this:

Dim LongLine as New Queue Dim X as Object LongLineEnqueue ( Tasha Korat ) LongLineEnqueue (725) LongLineEnqueue ( Gray ) X = LongLinePeek

The preceding code assigns the value Tasha Korat to the X variable, which is declared as an Object data type (In Visual BasicNET, an Object data type can hold any type of data including integers, strings, and decimal numbers, such as 5798) The Peek command only retrieves the data but leaves it at the front of the queue Figure 4-6 shows the difference between the Peek and the Dequeue commands