Introduction to Programming in Java: Standard Libraries

Input and output libraries.

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

§ PROGRAM DESCRIPTION / JAVADOC

1.5 StdIn.java read numbers and strings from standard input

1.5 StdOut.java write numbers and strings 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 data from files and websites

3.1 Out.java write data to files

3.1 Draw.java draw geometric shapes

3.1 Picture.java process images

3.2 Stopwatch.java measure running time

§	PROGRAM	DESCRIPTION / JAVADOC
1.5	StdIn.java	read numbers and strings from standard input
1.5	StdOut.java	write numbers and strings 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 data from files and websites
3.1	Out.java	write data to files
3.1	Draw.java	draw geometric shapes
3.1	Picture.java	process images
3.2	Stopwatch.java	measure running time

The file stdlib.jar bundles together all of the I/O libraries above into a .jar file.

Accessing the libraries.

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. The file stdlib.jar bundles together all of our standard libraries into one file. 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? The libraries in stdlib.jar are in the "default" package.

A. 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.