Question

Explain this java code, please.

import java.util.Scanner;

public class Program11
{
public static void main(String[] args)
{
Scanner stdIn = new Scanner(System.in);

final int maxSize = 128;
String[] titles = new String[maxSize];
int[] lengths = new int[maxSize];
int numDVDs = 0;
String op;

op = menu(stdIn);
System.out.println();
while (!op.equalsIgnoreCase("q"))
{
if (op.equalsIgnoreCase("a"))
{
if (numDVDs < maxSize)
numDVDs = addDVD(titles, lengths, numDVDs, stdIn);
}
else if (op.equalsIgnoreCase("t"))
searchByTitle(titles, lengths, numDVDs, stdIn);   
else if (op.equalsIgnoreCase("l"))
searchByLength(titles, lengths, numDVDs, stdIn);

System.out.println('\n');
op = menu(stdIn);
System.out.println();
}
}

public static String menu(Scanner stdIn)
{
String op;

System.out.println("***************************");
System.out.println("A Add a DVD *");
System.out.println("T Search by Title *");
System.out.println("L Search by Length *");
System.out.println("Q Quit *");
System.out.println("***************************");
do
{
System.out.print("Please enter an option : ");
op = stdIn.next();
} while (!(op.equalsIgnoreCase("a") || op.equalsIgnoreCase("t") || op.equalsIgnoreCase("l")
|| op.equalsIgnoreCase("q")));
System.out.println("***************************");

return op;
}

public static int addDVD(String[] titles, int[] lengths, int numDVDs, Scanner stdIn)
{
String title;
int length;

System.out.print("Please enter DVD title : ");
// last input used .next()
title = stdIn.nextLine();
title = stdIn.nextLine();
System.out.print("Please enter DVD length : ");
length = stdIn.nextInt();

// add in-order this time

// find index to add new item
int addLoc = numDVDs;
for (int i = 0; i < numDVDs; ++i)
if (titles[i].compareTo(title) >= 0)
{
addLoc = i;
i = numDVDs;
}

// make room for new item
for (int i = numDVDs; i > addLoc; --i)
{
titles[i] = titles[i-1];
lengths[i] = lengths[i-1];
}

// add new item
titles[addLoc] = title;
lengths[addLoc] = length;

return numDVDs + 1;
}

public static int bSearch(String[] titles, int numDVDs, String title, boolean trim)
{
int start = 0;
int end = numDVDs - 1;
while ( start <= end )
{
int mid = (start + end) / 2;

// exact match or trimmed match
String thisTitle = titles[mid];
if (trim && thisTitle.length() >= title.length())
thisTitle = thisTitle.substring(0, title.length());
//
  
if (thisTitle.compareTo(title) < 0)
start = mid + 1;
else if (thisTitle.compareTo(title) > 0)
end = mid - 1;
else
return mid;
}

return -1;
}
  
public static boolean startsWith(String str, String prefix)
{
if (str.length() < prefix.length())
return false;
else
return prefix.equals(str.substring(0, prefix.length()));
}

public static void searchByTitle(String[] titles, int[] lengths, int numDVDs, Scanner stdIn)
{
String title;

System.out.print("Please enter DVD title (post * allowed) : ");
// last input used .next()
title = stdIn.nextLine();
title = stdIn.nextLine();

System.out.println();
System.out.println("Title\t\tLength");
System.out.println("-----------------------------");
  
// wild card search
int tl = title.length();
if (tl > 0 && title.charAt(tl-1) == '*')
{
String tss = title.substring(0, tl-1);
// try to find an index where there is a match
int aLoc = bSearch(titles, numDVDs, tss, true);
// if at least one
if (aLoc != -1)
{
// probe at and left
int d = aLoc;
while (d >= 0 && startsWith(titles[d], tss))
{
System.out.println(titles[d] + "\t" + lengths[d] + "min");
--d;
}
// probe right
d = aLoc + 1;
while (d < numDVDs && startsWith(titles[d], tss))
{
System.out.println(titles[d] + "\t" + lengths[d] + "min");
++d;
}
}
}
// standard search
else
{
int loc = bSearch(titles, numDVDs, title, false);
if (loc != -1)
System.out.println(titles[loc] + "\t" + lengths[loc] + "min");
}
System.out.println();
}

public static void searchByLength(String[] titles, int[] lengths, int numDVDs, Scanner stdIn)
{
String sLength;
char lengthMod;
int length;

System.out.print("Please enter DVD length (pre < = > manditory) : ");
sLength = stdIn.next();
lengthMod = sLength.charAt(0);

System.out.println();
System.out.println("Title\t\tLength");
System.out.println("---------------------------------------");
if (lengthMod == '<')
{
length = Integer.parseInt(sLength.substring(1, sLength.length()));
for (int d = 0; d < numDVDs; ++d)
if (lengths[d] < length)
System.out.println(titles[d] + "\t" + lengths[d] + "min");
}
else if (lengthMod == '=')
{
length = Integer.parseInt(sLength.substring(1, sLength.length()));
for (int d = 0; d < numDVDs; ++d)
if (lengths[d] == length)
System.out.println(titles[d] + "\t" + lengths[d] + "min");
}
else if (lengthMod == '>')
{
length = Integer.parseInt(sLength.substring(1, sLength.length()));
for (int d = 0; d < numDVDs; ++d)
if (lengths[d] > length)
System.out.println(titles[d] + "\t" + lengths[d] + "min");
}
else
System.out.println("Format Error!");

System.out.println();
}
}