1    /* 
2     * Program featuring an array to store and interactively manipulate a list of numbers. 
3     */
4    
5    package arrayplay;
6    
7    import java.io.File;
8    import java.io.FileNotFoundException;
9    import java.util.Scanner;
10   
11       public class NumberList {
12           // VARIABLES LOCAL TO THE CLASS, AND HENCE GLOBAL TO THE METHODS
13           private static final int LIMIT = 1000;
14           private static int[] numbers = new int[LIMIT];
15           private static int numberOfNumbers = 0;
16           private static Scanner commandReader = new Scanner(System.in);
17   
18           public static void main(String[] args) {
19               try {
20                   // ESTABLISH THE ARRAY OF NUMBERS
21                   readNumbers();
22                   // CHECK THE DATA
23                   // System.out.println("nThe original list of numbers ...");
24                   // displayNumbers();
25                   // ENTER THE INTERPRETER
26                   interpreter();
27               } catch (FileNotFoundException ex) {
28                   System.out.println("The file was not found. Please think again.");
29                   System.exit(-1);
30               }
31           }
32   
33           // Assuming that the data file will be found in the public_html/data
34           // subdirectory of the user’s home directory.
35           private static Scanner establishScanner() throws FileNotFoundException {
36               String separator = File.separator;
37               String homeDirectory = System.getProperty("user.home");
38               String path = homeDirectory + separator + "public_html" + separator + "data" + separator;
39               String fullFileName = path + "NumberSet.txt";
40               return new Scanner(new File(fullFileName));
41           }
42   
43           private static void readNumbers() throws FileNotFoundException {
44               Scanner scanner = establishScanner();
45               while (scanner.hasNext()) {
46                   numbers[numberOfNumbers] = scanner.nextInt();
47                   numberOfNumbers = numberOfNumbers + 1;
48               }
49           }
50   
51           private static void displayNumbers() {
52               for (int x = 0; x < numberOfNumbers; x = x + 1) {
53                   System.out.println(numbers[x]);
54               }
55           }
56   
57           private static void interpreter() {
58               System.out.print(">>> ");
59               String command = commandReader.next();
60               if (command.equalsIgnoreCase("DISPLAY")) {
61                   interpreterDisplayCommand();
62               } else if (command.equalsIgnoreCase("PRINT")) {
63                   interpretPrintCommand();
64               } else if (command.equalsIgnoreCase("SWAP")) {
65                   interpretSwapCommand();
66               } else if (command.equalsIgnoreCase("ADD")) {
67                   interpretAddCommand();
68               } else if (command.equalsIgnoreCase("HELP")) {
69                   interpretHelpCommand();
70               } else if (command.equalsIgnoreCase("EXIT")) {
71                   System.exit(0);
72               } else {
73                   System.out.println("### Unrecognizable command: " + command);
74               }
75               interpreter();
76           }
77   
78           private static void interpreterDisplayCommand() {
79               displayNumbers();
80           }
81   
82           private static void interpretPrintCommand() {
83               String operand = commandReader.next();
84               if (operand.equalsIgnoreCase("FIRST")) {
85                   System.out.println(numbers[0]);
86               } else if (operand.equalsIgnoreCase("LAST")) {
87                   System.out.println(numbers[numberOfNumbers - 1]);
88               } else {
89                   int index = Integer.valueOf(operand);
90                   System.out.println(numbers[index - 1]);
91               }
92           }
93   
94           private static void interpretHelpCommand() {
95               System.out.println("HELP - display a menu of commands");
96               System.out.println("DISPLAY - display the list of numbers");
97               System.out.println("PRINT - print a number (FIRST;LAST;nth)");
98               System.out.println("SWAP - exchange two elements (nth;mth)");
99               System.out.println("ADD - add a number to the list (FIRST;LAST)");
100              System.out.println("EXIT - terminate execution of the program");
101          }
102  
103          private static void interpretSwapCommand() {
104              int position1 = commandReader.nextInt();
105              int position2 = commandReader.nextInt();
106              int temp = numbers[position1 - 1];
107              numbers[position1 - 1] = numbers[position2 - 1];
108              numbers[position2 - 1] = temp;
109          }
110  
111          private static void interpretAddCommand() {
112              String position = commandReader.next();
113              if (position.equalsIgnoreCase("LAST")) {
114                  addLast();
115              } else if (position.equalsIgnoreCase("FIRST")) {
116                  addFirst();
117              } else {
118                  System.out.println("### invalid operand for add command");
119              }
120              numberOfNumbers = numberOfNumbers + 1;
121          }
122  
123          private static void addLast() {
124              numbers[numberOfNumbers] = commandReader.nextInt();
125          }
126  
127          private static void addFirst() {
128              for (int x = numberOfNumbers; x > 0; x = x - 1) {
129                  numbers[x] = numbers[x - 1];
130              }
131              numbers[0] = commandReader.nextInt();
132          }
133    }