Processing what is an array

Suppose you want to delete the player at index k in playerList. The number of players goes down by one, so one fewer space is used in the array. If you are not worried about keeping the players in any particular order, then one way to delete player number k is to move the player from the last occupied position in the array into position k and then to decrement the value of playerCt :. The player previously in position k is no longer in the array, so we have deleted that player from the list.

The player previously in position playerCt - 1 is now in the array twice. But it's only in the occupied or valid part of the array once, since playerCt has decreased by one.

Remember that every element of the array has to hold some value, but only the values in positions 0 through playerCt - 1 will be looked at or processed in any way. By the way, you should think about what happens if the player that is being deleted is in the last position in the list. The code does still work in this case. What exactly happens? Suppose that when deleting the player in position k , you'd like to keep the remaining players in the same order. Maybe because they take turns in the order in which they are stored in the array.

And so on. The code for this is. Here is an illustration of the two ways of deleting an item from a partially full array. Here, player "C" is being deleted:. This leaves open the question of what happens when a partially full array becomes full, but you still want to add more items to it? We can't change the size of the array—but we can make a new, bigger array and copy the data from the old array into the new array. But what does it mean to copy an array in the first place?

Suppose that A and B are array variables, with the same base type, and that A already refers to an array. Suppose that we want B to refer to a copy of A. The first thing to note is that the assignment statement. Arrays are objects, and an array variable can only hold a pointer to an array.

The assignment statement copies the pointer from A into B , and the result is that A and B now point to the same array. For example, A[0] and B[0] are just different names for exactly the same array element. To make B refer to a copy of A , we need to make an entirely new array and copy all the items from A into B.

Let's say that A and B are of type double[]. Then to make a copy of A , we can say. To solve the problem of adding to a partially full array that has become full, we just need to make a new array that is bigger than the existing array.

The usual choice is to make a new array twice as big as the old. We need to meet one more requirement: At the end, the variable that referred to the old array must now point to the new array.

That variable is what gives us access to the data, and in the end, the data is in the new array. Fortunately, a simple assignment statement will make the variable point to the correct array. Let's suppose that we are using playerList and playerCt to store the players in a game, as in the example above, and we want to add newPlayer to the game. Here is how we can do that even if the playerList array is full:. After the new array has been created, there is no longer any variable that points to the old array, so it will be garbage collected.

Copying an array seems like such a common method that you might expect Java to have a built-in method already defined to do it. In fact, Java comes with several standard array-processing methods.

The methods are defined as static methods in a class named Arrays , which is in the package java. For example, for any array, list ,. If lengthOfCopy is greater than list. If lengthOfCopy is less than or equal to list. So if A is any array, then. We can also use Arrays. We might want to do that to avoid having a lot of excess, unused spaces.

To implement this idea, the code for deleting player number k from the list of players might become. I should mention that class Arrays actually contains a bunch of copyOf methods, one for each of the primitive types and one for objects. I should also note that when an array of objects is copied, it is only pointers to objects that are copied into the new array.

The contents of the objects are not copied. This is the usual rule for assignment of pointers. If what you want is a simple copy of an array, with the same size as the original, there is an even easier way to do it.

Every array has an instance method named clone that makes a copy of the array. To get a copy of an int array, A , for example, you can simply say. The Arrays class contains other useful methods. I'll mention a few of them. As with Arrays. One of the examples in Subsection 6. When the user clicks the program window, the positions, colors, and fonts are changed to new random values.

But suppose that we want the message strings to move. That is, we want to run an animation where the strings drift around in the window.

In that case, we need to store the properties of each string, since they will be needed to redraw the strings in each frame of the animation. A new version of the program that does that is RandomStringsWithArray. There are 25 strings.

We need to store the x,y coordinates where each string is drawn, the color of each string, and the font that is used for each string. Displaying these values each frame creates a trail behind the cursor. The following example produces the same result as the previous one but uses a more efficient technique.

Instead of shifting the array elements in each frame, the program writes the new data to the next available array position. The elements in the array remain in the same position once they are written, but they are read in a different order each frame. Reading begins at the location of the oldest data element and continues to the end of the array. This technique, commonly known as a ring buffer, is especially useful with larger arrays, to avoid unnecessary copying of data that can slow down a program.

Processing provides a group of functions that assist in managing array data. Only four of these functions are introduced here, but more are explained in the Processing reference included with the software. The append function expands an array by one element, adds data to the new position, and returns the new array:. The shorten function decreases an array by one element by removing the last element and returns the shortened array:.

The expand function increases the size of an array. It can expand to a specific size, or if no size is specified, the array's length will be doubled.

If an array needs to have many additional elements, it's faster to use expand to double the size than to use append to continually add one value at a time. The following example saves a new mouseX value to an array every frame.

When the array becomes full, the size of the array is doubled and new mouseX values proceed to fill the enlarged array. Array values cannot be copied with the assignment operator because they are objects. The most common way to copy elements from one array to another is to use special functions or to copy each element individually within a for loop. The arrayCopy function is the most efficient way to copy the entire contents of one array to another. The data is copied from the array used as the first parameter to the array used as the second parameter.

Both arrays must be the same length for it to work in the configuration shown here. New functions can be written to perform operations on arrays, but arrays behave differently than data types such as int and char. As with objects, when an array is used as a parameter to a function, the address location in memory of the array is transferred into the function instead of the actual data.

No new array is created, and changes made within the function affect the array used as the parameter. In the following example, the data[] array is used as the parameter to halve. The address of data[] is passed to the d[] array in the halve function.

Because the address of d[] and data[] is the same, they both point to the same data. Changes made to d[] on line 14 modify the value of data[] in the setup block. The draw function is not used because the calculation is made only once and nothing is drawn to the display window. Changing array data within a function without modifying the original array requires some additional lines of code.

In the following example, the array is passed into the function as a parameter, a new array is made, the values from the original array are copied in the new array, changes are made to the new array, and finally the modified array is returned.

Working with arrays of objects is technically similar to working with arrays of other data types, but it opens the amazing possibility to create as many instances of a custom-designed class as desired. Like all arrays, an array of objects is distinguished from a single object with brackets, the [ and ] characters.

However, because each array element is an object, each must be created with the keyword new before it can be used. The steps for working with an array of objects are:. These steps are translated into code in the following example.

It uses the Ring class from page , so copy it over or retype it. This code creates a rings[] array to hold fifty Ring objects. Space in memory for the rings[] array is allocated in setup and each Ring object is created. The first time a mouse button is pressed, the first Ring object is turned on and its x and y variables are assigned to the current values of the cursor.

Class Name Array. Description An array is a list of data. Parameters datatype any primitive or compound datatype, including user-defined classes var any valid variable name element int: must not exceed the length of the array minus 1 value data to assign to the array element; must be the same datatype as the array.

In use.