1    /* 
2     * Program featuring an array to store and interactively manipulate a list of numbers. 
3    */
4    package arrayplay;
5    
6    import java.io.File;
7    import java.io.FileNotFoundException;
8    import java.util.Scanner;
9    
10   public class NumberList {
11       // VARIABLES LOCAL TO THE CLASS, AND HENCE GLOBAL TO THE METHODS
12       private static final int LIMIT = 1000;
13       private static int[] numbers = new int[LIMIT];
14       private static int numberOfNumbers = 0;
15       private static Scanner commandReader = new Scanner(System.in);
16   
17       public static void main(String[] args) {
18           try {
19               // ESTABLISH THE ARRAY OF NUMBERS
20               readNumbers();
21               // CHECK THE DATA
22               System.out.println("nThe original list of numbers ...");
23               displayNumbers();
24               // ENTER THE INTERPRETER
25               interpreter();
26           } catch (FileNotFoundException ex) {
27               System.out.println("The file was not found. Please think again.");
28               System.exit(-1);
29           }
30       }
31   
32       // Assuming that the data file will be found in the public_html/data
33       // subdirectory of the user’s home directory.
34       private static Scanner establishScanner(String fn) throws FileNotFoundException {
35           String separator = File.separator;
36           String homeDirectory = System.getProperty("user.home");
37           String path = homeDirectory + separator + "CS1Files" + separator + "data" + separator;
38           String fullFileName = path + fn;
39           return new Scanner(new File(fullFileName));
40       }
41   
42       private static void readNumbers() throws FileNotFoundException {
43           Scanner scanner = establishScanner("NumberSet.txt");
44           while (scanner.hasNext()) {
45               numbers[numberOfNumbers] = scanner.nextInt();
46               numberOfNumbers = numberOfNumbers + 1;
47           }
48       }
49   
50       private static void displayNumbers() {
51           for (int x = 0; x < numberOfNumbers; x = x + 1) {
52               System.out.println(numbers[x]);
53           }
54       }
55   
56       private static void interpreter() {
57           System.out.print(">>> ");
58           String command = commandReader.next();
59           if (command.equalsIgnoreCase("DISPLAY")) {
60               interpreterDisplayCommand();
61           } else if (command.equalsIgnoreCase("PRINT")) {
62               interpretPrintCommand();
63           } else if (command.equalsIgnoreCase("SWAP")) {
64               interpretSwapCommand();
65           } else if (command.equalsIgnoreCase("ADD")) {
66               interpretAddCommand();
67           } else if (command.equalsIgnoreCase("HELP")) {
68               interpretHelpCommand();
69           } else if (command.equalsIgnoreCase("EXIT")) {
70               System.exit(0);
71           } else {
72               System.out.println("### Unrecognizable command: " + command);
73           }
74           interpreter();
75       }
76   
77       private static void interpreterDisplayCommand() {
78           displayNumbers();
79       }
80   
81       private static void interpretPrintCommand() {
82           String operand = commandReader.next();
83           if (operand.equalsIgnoreCase("FIRST")) {
84               System.out.println(numbers[0]);
85           } else if (operand.equalsIgnoreCase("LAST")) {
86               System.out.println(numbers[numberOfNumbers - 1]);
87           } else {
88               int index = Integer.valueOf(operand);
89               System.out.println(numbers[index - 1]);
90           }
91       }
92   
93       private static void interpretHelpCommand() {
94           System.out.println("HELP - display a menu of commands");
95           System.out.println("DISPLAY - display the list of numbers");
96           System.out.println("PRINT - print a number (FIRST;LAST;nth)");
97           System.out.println("SWAP - exchange two elements (nth;mth)");
98           System.out.println("ADD - add a number to the list (FIRST;LAST)");
99           System.out.println("EXIT - terminate execution of the program");
100      }
101  
102      private static void interpretSwapCommand() {
103          int position1 = commandReader.nextInt();
104          int position2 = commandReader.nextInt();
105          int temp = numbers[position1 - 1];
106          numbers[position1 - 1] = numbers[position2 - 1];
107          numbers[position2 - 1] = temp;
108      }
109  
110      private static void interpretAddCommand() {
111          String position = commandReader.next();
112          if (position.equalsIgnoreCase("LAST")) {
113              addLast();
114          } else if (position.equalsIgnoreCase("FIRST")) {
115              addFirst();
116          } else {
117              System.out.println("### invalid operand for add command");
118          }
119          numberOfNumbers = numberOfNumbers + 1;
120      }
121  
122      private static void addLast() {
123          numbers[numberOfNumbers] = commandReader.nextInt();
124      }
125  
126      private static void addFirst() {
127          for (int x = numberOfNumbers; x > 0; x = x - 1) {
128              numbers[x] = numbers[x - 1];
129          }
130          numbers[0] = commandReader.nextInt();
131      }
132  }