Standard Libraries

Standard libraries.

Below is a table of the input and output libraries that we use throughout the textbook and beyond.

Using the standard libraries.

The file stdlib.jar bundles together all of our standard libraries into one file. There are a number of ways to access the libraries:

• Current directory. The easiest (but not the sanest) way to use the standard libraries to download stdlib.jar and unjar it in your current working directory.
 % jar xf stdlib.jar 
Alternatively, you can download the individual .java files you need (such as StdIn.java) and put them in the same directory as the program you are writing. Then, compile and execute as usual.
 % javac MyProgram.java % java  MyProgram 
This approach has the drawback that you need a copy of each .java file you need in each directory where you need it.

• Classpath. Put stdlib.jar in the same directory as the program you are writing (but do not unjar it). 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.

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 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.

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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

Q + A

Q. Can I use your code in my project?

A. Our library stdlib.jar is released under the GNU General Public License, version 3 (GPLv3). If you wish to license the code under different terms, please contact our publisher to discuss.

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 libraries with a named package, you can use the packaged version stdlib-package.jar.

Warning: if you are taking Princeton COS 126, you must use the default package verison of our libraries to facilitate grading.