java数据结构与算法数组模拟队列示例详解

package sparsearray;

import java.util.Scanner;

public class MyArrayQueue {

     public static void main(String[] args) {

         // 创建一个队列

         ArrayQueue arrayQueue = new ArrayQueue( 3 );

         char key = ' ' ; //接受用户输入

         Scanner scanner = new Scanner(System.in);

         boolean loop = true ;

         // 输出一个菜单

         while (loop) {

             System.out.println( "s(show): 显示队列" );

             System.out.println( "e(exit): 退出程序" );

             System.out.println( "a(add): 添加数据到队列" );

             System.out.println( "g(get): 从队列取出数据" );

             System.out.println( "h(head): 显示队首的数据" );

             key = scanner.next().charAt( 0 ); // 接收一个字符

             switch (key) {

                 case 's' :

                     arrayQueue.showQueue();

                     break ;

                 case 'a' :

                     System.out.println( "请要添加的数" );

                     int value = scanner.nextInt();

                     arrayQueue.addQueue(value);

                     break ;

                 case 'g' :

                     try {

                         int res = arrayQueue.getQueue();

                         System.out.printf( "取出的数据是：%d" , res);

                     } catch (Exception e) {

                         System.out.println(e.getMessage());

                     }

                     break ;

                 case 'h' :

                     try {

                         int headValue = arrayQueue.showHeadQueue();

                         System.out.printf( "队首数据是：%d" , headValue);

                     } catch (Exception e) {

                         System.out.println(e.getMessage());

                     }

                     break ;

                 case 'e' :

                     scanner.close();

                     loop = false ;

                     break ;

             }

         }

         System.out.println( "退出程序" );

     }

}

// 把队列抽象成一个类，ArrayQueue

class ArrayQueue {

     //表示数组最大容量

     private int maxSize;

     // 队列头

     private int front;

     // 队列尾

     private int rear;

     // 用于存放数据的数组

     private int [] arr;

     // 构造器

     public ArrayQueue( int arrMaxSize) {

         maxSize = arrMaxSize;

         arr = new int [maxSize];

         front = - 1 ; // 指向队首的前一个位置

         rear = - 1 ; // 指向队列尾部，包括队列最后的这个数据

     }

     // 判断队列是否已经存满

     public boolean isFull() {

         return rear == maxSize - 1 ; // 注意这里的 maxSize-1 为什么要减1

     }

     // 判断队列是否为空

     public boolean isEmpty() {

         return rear == front;

     }

     // 添加数据到队列

     public void addQueue( int num) {

         // 判断队列是否满了

         if (isFull()) {

             System.out.println( "队列已满，不可加入数据" );

             return ;

         }

         rear++; // 让rear后移

         arr[rear] = num;

     }

     // 拿出队列数据

     public int getQueue() {

         // 判断队列是否空

         if (isEmpty()) {

             // 抛出异常

             throw new RuntimeException( "队列为空，不可取数据" );

         }

         front++; // front后移

         return arr[front];

     }

     // 显示队列所有数据

     public void showQueue() {

         // 遍历

         if (isEmpty()) {

             System.out.println( "队列为空" );

             return ;

         }

         for ( int i = 0 ; i < arr.length; i++) {

             System.out.printf( "arr[%d]=%d\n" , i, arr[i]);

         }

     }

     // 显示队里的队首数据

     public int showHeadQueue() {

         if (isEmpty()) {

             // 抛出异常

             throw new RuntimeException( "队列为空，不可取数据" );

         }

         return arr[front + 1 ]; // 注意这里为甚么要+1，因为指向队首的前一个位置

     }

}