Standard Libraries

Here is a list of the input and output libraries that we use throughout the textbook and beyond.

§	PROGRAM	DESCRIPTION / JAVADOC
1.5	StdIn.java	read numbers and text from standard input
1.5	StdOut.java	write numbers and text to standard output
1.5	StdDraw.java	draw geometric shapes in a window
1.5	StdAudio.java	create, play, and manipulate sound
2.2	StdRandom.java	generate random numbers
2.2	StdStats.java	compute statistics
2.2	StdArrayIO.java	read and write 1D and 2D arrays
3.1	In.java	read numbers and text from files and URLs
3.1	Out.java	write numbers and text to files
3.1	Draw.java	draw geometric shapes
3.1	Picture.java	process digital images
3.2	Stopwatch.java	measure running time
-	BinaryStdIn.java	read bits from standard input
-	BinaryStdOut.java	write bits to standard output
-	BinaryIn.java	read bits from files and URLs
-	BinaryOut.java	write bits to files

The file stdlib.jar bundles together all of our standard libraries into one file. The easiest way to use is to unjar them in your current working directory.

% jar xf stdlib.jar

We briefly describe the input and output libraries and include a sample client.

Standard input and standard output.

StdIn.java and StdOut.java are libraries for reading in numbers and text from standard input and printing out numbers and text to standard output. Our versions have a simpler interface than the corresponding Java ones (and provide a few tecnical improvements). Average.java reads in a sequence of real numbers from standard input and prints their average on standard output.

% java Average
10.0 5.0 6.0 3.0 7.0 32.0
3.14 6.67 17.71
<Ctrl-d>
Average is 10.05777777777778

In.java and Out.java are object-oriented versions that support multiple input and output streams, including reading from a file or URL and writing to a file. Wget.java reads in data from the URL specified on the command line and save it in a file with the same name.

% java Wget http://www.cs.princeton.edu/IntroProgramming/datafiles/codes.csv
% more codes.csv
United States,USA,00
Alabama,AL,01
Alaska,AK,02
...

Binary standard input and standard output.

BinaryStdIn.java and BinaryStdOut.java are the analogs for binary data. Copy.java reads a binary file from standard input and writes it to standard output.

% java Copy < mandrill.jpg > copy.jpg
% diff mandrill.jpg copy.jpg

Standard drawing.

StdDraw.java is an easy-to-use library for drawing geometric shapes, such as points, lines, and circles. RightTriangle.java draws a right triangle and a circumscribing circle.

% java RightTriangle

BouncingBall.java illustrates how to produce an animation using standard drawing.

Your browser can not display this movie.
Be sure that Javascript is enabled and that you have Flash 9.0.124 or better.

Draw.java is an object-oriented versions that support drawing in multiple windows.

Standard audio.

StdAudio.java is an easy-to-use library for synthesizing sound. Tone.java reads in a frequency and duration from the command line, and it sonifies a sine wave of the given frequency for the given duration.

% java Tone 440.0 3.0

Image processing.

Picture.java is an easy-to-use library for image processing. Scale.java takes the name of a picture file and two integers (width w and height h) as command-line arguments and scales the image to w-by-h.

% java Scale mandrill.jpg 298 298

% java Scale mandrill.jpg 200 200

% java Scale mandrill.jpg 200 400

Using the standard libraries in your programs.

There are a number of ways to access the libraries:

Current directory. The simplest method is to put the desired .java file (such as StdIn.java) in the same directory as the program you are writing. Then, compile and execute as usual.
% javac MyProgram.java % java MyProgram

Classpath. To access it, put stdlib.jar in the same directory as the program you are writing. Then, compile and execute as follows.

OS X / Linux
------------
% javac -cp .:stdlib.jar MyProgram.java
% java  -cp .:stdlib.jar MyProgram

Windows
------------
% javac -cp .;stdlib.jar MyProgram.java
% java  -cp .;stdlib.jar MyProgram

The -cp flag sets the classpath. The . tells Java to look in the current directory for .java and .class files (such as MyProgram.java and MyProgram.class). The stdlib.jar tells Java to also look in the .jar file. On OS X, the : separates directories in the classpath; on Windows the ; separates directories.

Configure your IDE. You can configure your IDE to automatically include stdlib.jar in the classpath. In DrJava, it is Preferences -> Extra Classpath -> Add.

Q. If I use a named package to structure my code, the compiler can no longer access the libraries in stdlib.jar. Why not?

A. The libraries in stdlib.jar are in the "default" package. In Java, you can't access classes in the default package from a named package. If you need to use our standard libraries with a named package, you must put our libraries in a package, as in this solution.