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