http:^^www.cs.wisc.edu^~cs537-1^java-tutorial.html

This data set contains WWW-pages collected from computer science departments of various universities

                    break;
                a[j+1] = a[j];
            }
            // now a[0..j] are all <= x and a[j+2..i] are > x
            a[j+1] = x;
        }
    }

    /** Test program to test sort */
    public static void main(String argv[]) {
        if (argv.length != 1) {
            System.out.println("usage: sort array-size");
            System.exit(1);
        }
        int size = Integer.parseInt(argv[0]);
        int test[] = new int[size];
        Random r = new Random();

        System.out.println("<" + 4 * Math.atan(1) + ">");
        for (int i = 0; i < size; i++)
            test[i] = (int)(r.nextFloat() * 100);
        System.out.println("before");
        for (int i = 0; i < size; i++)
            System.out.println(test[i]);

        sort(test, size);

        System.out.println("after");
        for (int i = 0; i < size; i++)
            System.out.println(test[i]);

        System.exit(0);
    }
}
</font></pre>
<p>
A copy of this program is available in
<!WA15><!WA15><!WA15><!WA15><!WA15><!WA15><a href="http://www.cs.wisc.edu/~cs537-1/examples/SortTest.java">
<samp>~cs537-1/public/examples/SortTest.java</samp>.
</a>
To try it out, create a new directory and copy the example to a file
named <samp><font color="0f0fff">SortTest.java</font></samp> in that directory.  (The file <em>must</em>
be called <samp><font color="0f0fff">SortTest.java</font></samp>!)
<pre><font color="0f0fff">
    mkdir test1
    cd test1
    cp ~cs537-1/public/examples/SortTest.java SortTest.java
    javac SortTest.java
    java SortTest 10
</font></pre>
(You can also grab a copy of the source with your net browser.
Visit
<!WA16><!WA16><!WA16><!WA16><!WA16><!WA16><a href="http://www.cs.wisc.edu/~cs537-1/examples/SortTest.java">
<samp>~cs537-1/public/examples/SortTest.java</samp>
</a>
and use the <em>Save As...</em> option from the <em>File</em> menu.)
<p>
The <samp><font color="0f0fff">javac</font></samp> command invokes the Java compiler on the source
file <samp><font color="0f0fff">SortTest.java</font></samp>.
If all goes well, it will create a file named <samp><font color="0f0fff">SortTest.class</font></samp>,
which contains code for the Java virtual machine.
The <samp><font color="0f0fff">java</font></samp> command invokes the Java interpreter to run the code
for class <samp><font color="0f0fff">SortTest</font></samp>.  Note that the first parameter is
<samp><font color="0f0fff">SortTest</font></samp>, not <samp><font color="0f0fff">SortTest.class</font></samp>
or <samp><font color="0f0fff">SortTest.java</font></samp> because it is the name of a <em>class</em>,
not a file.
<p>
There are several things to note about this program.
First, Java has no ``top-level'' or ``global'' variables or functions.
A Java program is <em>always</em> a set of <samp><font color="0f0fff">class</font></samp> definitions.
Thus, we had to make <samp><font color="0f0fff">sort</font></samp> and <samp><font color="0f0fff">main</font></samp> member functions
(called ``methods'' in Java) of a class, which we called
<samp><font color="0f0fff">SortTest</font></samp>.
<p>
Second, the <samp><font color="0f0fff">main</font></samp> function is handled somewhat differently in
Java from C++.
In C++, the first function to be executed is always a function called
<samp><font color="0f0fff">main</font></samp>, which has two arguments and return an integer value.
The return value is the ``exit status'' of the program; by convention,
a status of zero means ``normal termination'' and anything else means
something went wrong.
The first argument is the number of words on the command-line that invoked
the program, and the second argument is a an array of character strings
(denoted <samp><font color="0f0fff">char *argv[]</font></samp> in C++) containing those words.
If we invoke the program by typing
<pre><font color="0f0fff">
    sort 10
</font></pre>
we will find that
<samp><font color="0f0fff">argc==2</font></samp>,
<samp><font color="0f0fff">argv[0]=="sort"</font></samp>, and
<samp><font color="0f0fff">argv[1]=="10"</font></samp>.
<p>
In Java, the first thing executed is the method called <samp><font color="0f0fff">main</font></samp>
of the indicated class (in this case <samp><font color="0f0fff">SortTest</font></samp>).
The <samp><font color="0f0fff">main</font></samp> method does not return any value (it is of type
<samp><font color="0f0fff">void</font></samp>).
For now, ignore the words ``<samp><font color="0f0fff">public static</font></samp>'' preceding
<samp><font color="0f0fff">void</font></samp>.  We will return to these later.
The <samp><font color="0f0fff">main</font></samp> method takes only one parameter, an array of strings
(denoted <samp><font color="0f0fff">String argv[]</font></samp> in Java).
This array will have one element for each word on the command line
<em>following</em> the name of the class being executed.
Thus in our example call,
<pre><font color="0f0fff">
    java SortTest 10
</font></pre>
<samp><font color="0f0fff">argv[0] == "10"</font></samp>.
There is no separate argument to tell you how many words there are,
but in Java, you can tell how big <em>any</em> array is by using
<samp><font color="0f0fff">length</font></samp>.
In this case <samp><font color="0f0fff">argv.length == 1</font></samp>, meaning <samp><font color="0f0fff">argv</font></samp>
contains only one word.
<p>
The third difference to note is the way I/O is done in Java.
<samp><font color="0f0fff">System.out</font></samp> in Java is roughly equivalent to <samp><font color="0f0fff">cout</font></samp>
in C++ (or <samp><font color="0f0fff">stdout</font></samp> in C), and
<pre><font color="0f0fff">
    System.out.println(whatever);
</font></pre>
is (even more) roughly equivalent to
<pre><font color="0f0fff">
    cout &lt;&lt; whatever &lt;&lt; endl;
</font></pre>
<p>
Our C++ program used three functions from the standard library,
<samp><font color="0f0fff">atoi</font></samp>, <samp><font color="0f0fff">random</font></samp>, and <samp><font color="0f0fff">exit</font></samp>.
<samp><font color="0f0fff">Integer.parseInt</font></samp> does the same thing as <samp><font color="0f0fff">atoi</font></samp>:
It converts the character-string "10" to the integer value ten,
and <samp><font color="0f0fff">System.exit(1)</font></samp> does the same thing as <samp><font color="0f0fff">exit(1)</font></samp>:
It immediately terminates the program, returning an exit status of 1
(meaning something's wrong).
The library class <samp><font color="0f0fff">Random</font></samp> defines random-number generators.
The statement <samp><font color="0f0fff">Random r = new Random()</font></samp> create an instance of
this class, and <samp><font color="0f0fff">r.nextFloat()</font></samp> uses it to generate a floating
point number between 0 and 1.
The <em>cast</em> <samp><font color="0f0fff">(int)</font></samp> means the same thing in Java as in C++.
It converts its floating-point argument to an integer, throwing away
the fraction.
<p>
Finally, note that the <samp><font color="0f0fff">#include</font></samp> directives from C++ have
been replaced by <samp><font color="0f0fff">import</font></samp> declarations.
Although they have roughly the same effect, the mechanisms are different.
In C++, <samp><font color="0f0fff">#include &lt;iostream.h&gt;</font></samp> pulls in a source file
called <samp><font color="0f0fff">iostream.h</font></samp> from a source library and compiles it along
with the rest of the program.
<samp><font color="0f0fff">#include</font></samp> is usually used to include files containing declarations
of library functions and classes, but the file could contain any C++
source code whatever.
The Java declaration <samp><font color="0f0fff">import java.util.Random</font></samp> brings in
the pre-compiled class <samp><font color="0f0fff">Random</font></samp> from a <em>package</em> called
<samp><font color="0f0fff">java.util</font></samp>.  The declaration <samp><font color="0f0fff">import java.io.*</font></samp>
bring in <em>all</em> of the classes defined in the package
<samp><font color="0f0fff">java.util</font></samp>.  A package is sort of like a library.
You won't have to worry much about packages for this course.

<a name="objects"><h2> Values, Objects, and Pointers </h2></a>
<p>
It is sometimes said that Java doesn't have pointers.
That is not true.
In fact, objects can <em>only</em> be referenced with pointers.
More precisely, variables can hold primitive values (such
as integers or floating-point numbers) or <em>pointers</em>
to objects.
A variable cannot hold an object, and you cannot make a pointer to
a primitive value.
Since you don't have a choice, Java doesn't have a special notation
like C++ does to indicate when you want to use a pointer.
<p>
There are exactly eight primitive types in Java,
<samp><font color="0f0fff">boolean</font></samp>,
<samp><font color="0f0fff">char</font></samp>,
<samp><font color="0f0fff">byte</font></samp>,
<samp><font color="0f0fff">short</font></samp>,
<samp><font color="0f0fff">int</font></samp>,
<samp><font color="0f0fff">long</font></samp>,
<samp><font color="0f0fff">float</font></samp>, and
<samp><font color="0f0fff">double</font></samp>.
Most of these are similar to types with the same name in C++.
We mention only the differences.
<p>
A <samp><font color="0f0fff">boolean</font></samp> value is either
<samp><font color="0f0fff">true</font></samp> or
<samp><font color="0f0fff">false</font></samp>.
You cannot use an <samp><font color="0f0fff">integer</font></samp>
where a <samp><font color="0f0fff">boolean</font></samp> is required
(e.g. in an <samp><font color="0f0fff">if</font></samp> or
<samp><font color="0f0fff">while</font></samp> statement)
nor is there any automatic conversion between
<samp><font color="0f0fff">boolean</font></samp>
and
<samp><font color="0f0fff">integer</font></samp>.
<p>
A <samp><font color="0f0fff">char</font></samp> value is 16 bits rather
than 8 bits, as it is in C or C++, to allow for all sorts of international
alphabets.
As a practical matter, however, you are unlikely to notice the difference.
The <samp><font color="0f0fff">byte</font></samp> type is 8 bits.
<p>
A <samp><font color="0f0fff">short</font></samp> is 16 bits and an
<samp><font color="0f0fff">int</font></samp> is 32 bits, just as in C or
C++ on most modern machines (in C++ the size is machine-dependent, but
in Java it's guaranteed).
A Java <samp><font color="0f0fff">long</font></samp> is <em>not</em>
the same as in C++ -- it is 64 bits long.
The types <samp><font color="0f0fff">float</font></samp>
and <samp><font color="0f0fff">double</font></samp> are just like in C++:
32-bit and 64-bit floating point.
<p>
As in C++, <em>objects</em> are <em>instances</em> of <em>classes</em>.
There is no prefix <samp><font color="0f0fff">*</font></samp> or <samp><font color="0f0fff">&amp;</font></samp> operator or
infix <samp><font color="0f0fff">-&gt;</font></samp> operator.
<p>
As an example, consider the class declaration (which is the same in
C++ and in Java)
<center>
<pre><font color="0f0fff">
class Point { int x, y; }
</font></pre>
<table frame="box"
    bgcolor="#e0e0ff"
    width="70%"
    border=3
    cellpadding=1
    cellspacing=1>
<tr><th>C++<th>Java
<tr><td><samp><font color="0f0fff">Point origin;</font></samp><td><samp><font color="0f0fff">Point origin = new Point();</font></samp>
<tr><td><samp><font color="0f0fff">Point *p, *q, *r;</font></samp><td><samp><font color="0f0fff">Point p, q, r;</font></samp>
<tr><td><samp><font color="0f0fff">origin.x = 0;</font></samp><td><samp><font color="0f0fff">origin.x = 0;</font></samp>
<tr><td><samp><font color="0f0fff">p = new Point;</font></samp><td><samp><font color="0f0fff">p = new Point();</font></samp>
<tr><td><samp><font color="0f0fff">p -> y = 5;</font></samp><td><samp><font color="0f0fff">p.y = 5;</font></samp>
<tr><td><samp><font color="0f0fff">q = p;</font></samp><td><samp><font color="0f0fff">q = p;</font></samp>
<tr><td><samp><font color="0f0fff">r = &origin;</font></samp><td><i>not possible</i>
</table>
<p>
<!WA17><!WA17><!WA17><!WA17><!WA17><!WA17><IMG ALIGN=TOP SRC="http://www.cs.wisc.edu/~cs537-1/objects.gif">.
</center>

<a name="garbage"><h2> Garbage Collection </h2></a>
<p>
New objects are create by the <samp><font color="0f0fff">new</font></samp> operator in Java just like C++
(except that an argument list is required after the class name, even
if the constructor for the class doesn't take any arguments so the list
is empty).
However, there is no <samp><font color="0f0fff">delete</font></samp> operator.
The Java system automatically deletes objects when no references to them
remain.
This is a much more important convenience than it may at first seem.
<samp><font color="0f0fff">delete</font></samp> operator is extremely error-prone.
Deleting objects too early can lead to <em>dangling</em> reference, as in
<pre><font color="0f0fff">
    p = new Point();
    // ...
    q = p;
    // ... much later
    delete p;
    q -&gt; x  = 5; // oops!
</font></pre>
while deleting them too late (or not at all) can lead to <em>garbage</em>,
also known as a <em>storage leak</em>.

<a name="access"><h2> Static, Final, Public, and Private </h2></a>
<p>
Just as in C++, it is possible to restrict access to members of a class
by declaring them <em>private</em>, but the syntax is different.
<br>
In C++:
<pre><font color="0f0fff">
    class C {
        private:
            int i;
            double d;