待解：Array; Queue

 1 package com.java7;
 2 /*
 3  * Try This 5-2
 4  * A queue class for characters.
 5  */
 6 class Queue {
 7     char q[]; // this array holds the queue
 8     int putloc, getloc; // the put and get indices
 9
10     Queue(int size) {
11         q = new char[size+1]; // allocate memory for queue
12         putloc = getloc = 0;
13     }
14
15     // put a character into the queue
16     void put(char ch) {
17         if(putloc==q.length-1){
18             System.out.println(" - Queue is full.");
19             return;
20         }
21
22         putloc++;
23         q[putloc] = ch;
24     }
25
26     // get a character from the queue
27     char get() {
28         if(getloc == putloc) {
29             System.out.println(" - Queue is empty.");
30             return (char) 0;
31         }
32
33         getloc++;
34         return q[getloc];
35     }
36 }
37
38 //Demonstrate the Queue class.
39 class QDemo {
40     public static void main(String[] args) {
41         Queue bigQ = new Queue(100);
42         Queue smallQ = new Queue(4);
43         char ch;
44         int i;
45
46         System.out.println("Using bigQ to store the alphabet.");
47         // put some numbers into bigQ
48         for(i = 0; i < 26; i++)
49             bigQ.put((char) (‘A‘ + i));
50
51         // retrieve and display elements from bigQ
52         System.out.print("Contents of bigQ: ");
53         for(i = 0; i < 26; i++) {
54             ch = bigQ.get();
55             if(ch != (char) 0) System.out.print(ch);
56         }
57
58         System.out.println("\n");
59
60         System.out.println("Using smallQ to generate errors.");
61         // Now, use smallQ to generate some errors
62         for(i = 0; i < 5; i++) {
63             System.out.print("Attempting to store " + (char) (‘Z‘ - i));
64             smallQ.put((char) (‘Z‘ - i));
65             System.out.println();
66         }
67         System.out.println();
68
69         // more errors on smallQ
70         System.out.print("Contents of smallQ: ");
71         for(i = 0; i < 5; i++) {
72             ch = smallQ.get();
73
74             if (ch != (char) 0) System.out.print(ch);
75         }
76     }
77 }

执行结果：

Using bigQ to store the alphabet.

Contents of bigQ: ABCDEFGHIJKLMNOPQRSTUVWXYZ

Using smallQ to generate errors.

Attempting to store Z

Attempting to store Y

Attempting to store X

Attempting to store W

Attempting to store V - Queue is full.

Contents of smallQ: ZYXW - Queue is empty.

练习2：尝试修改Queue，以使其存储其他类型的对象。