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       public static Scanner establishScanner(String fn) throws FileNotFoundException {
32           String separator = File.separator;
33   //        String homeDirectory = System.getProperty("user.home");
34           String path = "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           }
59           else if (command.equalsIgnoreCase("PRINT")) {
60               interpreterPrintCommand();
61           }
62           else if (command.equalsIgnoreCase("SWAP")) {
63               interpreterSwapCommand();
64           }
65           else if (command.equalsIgnoreCase("ADD")) {
66               interpreterAddCommand();
67           }
68           else if (command.equalsIgnoreCase("HELP")) {
69               interpreterHelpCommand();
70           }
71           else if (command.equalsIgnoreCase("EXIT")) {
72               System.exit(0);
73           }
74           else {
75               System.out.println("### Unrecognizable command: " + command);
76           }
77           interpreter();
78       }
79   
80       private static void interpreterDisplayCommand() {
81           displayNumbers();
82       }
83   
84       private static void interpreterPrintCommand() {
85           String operand = commandReader.next();
86           if (operand.equalsIgnoreCase("FIRST")) {
87               System.out.println(numbers[0]);
88           }
89           else if (operand.equalsIgnoreCase("LAST")) {
90               System.out.println(numbers[numberOfNumbers - 1]);
91           }
92           else {
93               int index = Integer.valueOf(operand);
94               System.out.println(numbers[index - 1]);
95           }
96       }
97   
98   
99       private static void interpreterHelpCommand() {
100          System.out.println("HELP - display the menu of commands");
101          System.out.println("DISPLAY - display the list of numbers");
102          System.out.println("PRINT - print the number (FIRST, LAST; nth");
103          System.out.println("SWAP - exchange two elements (nth;mth)");
104          System.out.println("ADD - add a number to the list (FIRST;LAST)");
105          System.out.println("EXIT - terminate the program");
106      }
107  
108      private static void interpreterSwapCommand() {
109          int position1 = commandReader.nextInt();
110          int position2 = commandReader.nextInt();
111          int temp = numbers[position1 - 1];
112          numbers[position1 - 1] = numbers[position2 - 1];
113          numbers[position2 -1] = temp;
114      }
115  
116      private static void interpreterAddCommand() {
117          String position = commandReader.next();
118          if (position.equalsIgnoreCase("LAST")) {
119              addLast();
120          }
121          else if (position.equalsIgnoreCase("FIRST")) {
122              addFirst();
123          }
124          else {
125              System.out.println("### invalid operand for add command");
126          }
127          numberOfNumbers = numberOfNumbers + 1;
128      }
129  
130      private static void addLast() {
131          numbers[numberOfNumbers] = commandReader.nextInt();
132      }
133  
134      private static void addFirst() {
135          for (int x = numberOfNumbers; x > 0; x = x - 1) {
136              numbers[x] = numbers[x - 1];
137          }
138          numbers[0] = commandReader.nextInt();
139      }
140  }