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   
34       // ASSUMING THAT THE DATA FILE WILL BE FOUND IN THE PUBLIC_HTML/DATA
35       // subdirectory of the user's home directory.
36       private static Scanner establishScanner(String fn) throws FileNotFoundException {
37           String separator = File.separator;
38           String homeDirectory = System.getProperty("user.home");
39           String path = homeDirectory + separator + "public_html" + separator + "data" + separator;
40           String fullFileName = path + fn;
41           return new Scanner(new File(fullFileName));
42       }
43   
44       private static void readNumbers() throws FileNotFoundException {
45           Scanner scanner = establishScanner("NumberSet.txt");
46           while (scanner.hasNext()) {
47               numbers[numberOfNumbers] = scanner.nextInt();
48               numberOfNumbers = numberOfNumbers + 1;
49   
50           }
51       }
52        private static void displayNumbers() {
53           for (int x = 0; x < numberOfNumbers; x = x + 1) {
54               System.out.println(numbers[x]);
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("### Unrecognisable 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  }
134