Standard data input
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Standard input makes it convenient for us to write programs that process arbitrary amounts of input and to interact with our programs; standard draw makes it possible for us to work with graphics; and standard audio adds sound.
A Java program takes input values from the command line and prints a string of characters as output. By default, both command-line arguments and standard output are associated with an application that takes commands, which we refer to as the terminal window.
Here are some instructions for using the command line on your system. All of our classes have a main method that takes a String array args as argument. That array is the sequence of command-line arguments that we type. If we intend for an argument to be a number, we must use a method such as Integer. To print output values in our programs, we have been using System.
Java sends the results to an abstract stream of characters known as standard output. By default, the operating system connects standard output to the terminal window. All of the output in our programs so far has been appearing in the terminal window. It takes a command-line argument n and prints to standard output a sequence of n random numbers between 0 and 1. To complete our programming model, we add the following libraries: Read numbers and strings from the user.
Nevertheless, to treat standard input and standard output in a uniform manner and to provide a few technical improvementswe use similar methods that are defined in our StdOut library: Java's print and println methods are the ones that you have been using. The printf method gives us more control over the appearance of the output.
In its simplest form, printf takes two arguments. The first argument is called the format string. It contains a conversion specification that describes how the second argument is to be converted to a string for output.
The following table summarizes the most frequently used codes: The format string can contain characters in addition to those for the conversion specification. The conversion specification is replaced by the argument value converted to a string as specified and all remaining characters are passed through to the output. The printf function can take more than two arguments. In this case, the format string will have an additional conversion specification for each additional argument.
Here is more documentation on printf format string syntax. Our StdIn library takes data from a standard input stream that contains a sequence of values separated by whitespace. Each value is a string or a value from one of Java's primitive types. One of the key features of the standard input stream is that your program consumes values when it reads them. Once your program has read a value, it cannot back up and read it again. The library is defined by the following API: We now consider several examples in detail.
When you use the java command to invoke a Java program from the command line, you actually are doing three things: The string of characters that you type in the terminal window after the command line is the standard input stream.
If you type abc or StdIn treats strings of consecutive whitespace characters as identical to one space and allows you to delimit your numbers with such strings. The program generates a random integer and then gives clues to a user trying to guess the number. The fundamental difference between this read analyze command line arguments in c; binary and decimal conversions and others that we have written is that the user has the ability to change the control flow while the program is executing.
Processing an arbitrary-size input stream. Typically, input streams are finite: But there is no restriction of the size of the input stream.
For many applications, typing input data as a standard input stream from the terminal window is untenable because doing so limits our program's processing power by the amount of data that we can type. Similarly, we often want to save the information printed on the standard output stream for later use.
We can use operating system mechanisms to address both issues. Redirecting standard output to a file. By adding read analyze command line arguments in c; binary and decimal conversions simple directive to the command that invokes a program, we can redirect its standard output to a file, either for permanent storage or for input to some other program at a later time.
For example, the command specifies that the standard output stream is not to be printed in the terminal window, but instead is to be written to a text file named data. Each call to StdOut. In this example, the end result is a file that contains 1, random values.
Redirecting standard output from a file. Similarly, we can redirect standard input so that StdIn reads data from a file instead of the terminal window.
For example, the command reads a sequence of numbers from the file data. When the program calls StdIn. This facility to redirect standard input from a file enables us to process huge amounts of data from any source with our programs, limited only by the size of the files that we can store.
The read analyze command line arguments in c; binary and decimal conversions flexible way to implement the standard input and standard output abstractions is to specify that they are implemented by our own programs! This mechanism is called piping. For example, the following command specifies that the standard output for RandomSeq and the standard input stream for Average are the same stream. For many common tasks, it is convenient to think of each program as a filter that converts a standard input stream to a standard output stream in some way, RangeFilter.
Your operating system also provides a number of filters. For example, the sort filter puts the lines on standard input in sorted order: Now we introduce a simple abstraction for producing drawings as output. We imagine an abstract drawing device capable of drawing lines and points on a two-dimensional canvas. The device is capable of responding to the commands that our programs issue in the form of calls to static methods read analyze command line arguments in c; binary and decimal conversions StdDraw.
The primary interface consists of two kinds of methods: We first consider the drawing commands: These methods are nearly self-documenting: The default coordinate scale is the unit square all x - and y -coordinates between 0 and 1. The standard implementation displays the canvas in a window on your computer's screen, with black lines and points on a white background. The HelloWorld for graphics programming with StdDraw is to draw a triangle with a point inside. The default canvas size is by pixels and the default coordinate system is the unit square, but we often want to draw plots at different scales.
Also, we often want to draw line segments of different thickness or points of different size from the standard. To accommodate these needs, StdDraw has the following methods: For example, the two-call sequence StdDraw. Filtering data to a standard drawing. It adopts the convention that the first four numbers on standard input specify the bounding box, so that it can scale the plot.
There are an infinite number of points in the interval, so we have to make do with evaluating the function at a finite number of points within the interval. We sample the function by choosing a set of x -values, then computing y -values by evaluating the function at each x -value.
Plotting the function by connecting successive points with lines produces what is known as a piecewise linear approximation. Outline and filled shapes. StdDraw also includes methods to draw circles, rectangles, and arbitrary polygons. Each shape defines an outline. When the method name is just the shape name, that outline is traced by the drawing pen.
When the method name begins with filledthe named shape is instead filled solid, not traced. The arguments for circle define a circle of radius r; the arguments for square define a square of side length 2r centered on the given point; and the arguments for polygon define a sequence of points that we connect read analyze command line arguments in c; binary and decimal conversions lines, including one from the last point to the first point.
To annotate or highlight various elements in your drawings, StdDraw includes methods for drawing text, setting the font, and setting the the ink in the pen. In this code, java. Color are abstractions that are implemented with non-primitive types that you will learn about in Section 3. Until then, we leave the details to StdDraw. The default ink color is black; the default font is a point plain Serif font.
StdDraw supports a powerful computer graphics feature known as double buffering. When double buffering is enabled by calling enableDoubleBufferingall drawing takes place on the offscreen canvas. The offscreen canvas is read analyze command line arguments in c; binary and decimal conversions displayed; it exists only in computer memory. Only when you call show does your read analyze command line arguments in c; binary and decimal conversions get copied from the offscreen canvas to the onscreen canvaswhere it is displayed in the standard drawing window.
You can think of double buffering as collecting all of the lines, points, shapes, and text that you tell it to draw, and then drawing them all simultaneously, upon request. One reason read analyze command line arguments in c; binary and decimal conversions use double buffering is for efficiency when performing a large number of drawing commands.
Our most important use of double buffering is to produce computer animationswhere we create the illusion of motion by rapidly displaying static drawings.
We can produce animations by repeating the following four steps: Clear the offscreen canvas. Draw objects on the offscreen Copy the offscreen canvas to the onscreen canvas.