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