Java课程上机实验1_ConnectionManager

题目要求：

Following the form of the example Lunch.java, create a class called ConnectionManager that manages a fixed array of Connection objects. The client programmer must not be able to explicitly create Connection objects, but can only get them via a static method in ConnectionManager. When the ConnectionManager runs out of objects, it returns a null reference. Test the classes in main( ).

 

设计思路：

　　Connection类的构造方法为私有类型，仅能通过其creatConnection()方法创建Connection对象；在ConnectionManager类中，有一静态Connection对象的引用数组cnns，存储10个Connection对象的引用，topPos 表示当前为null的元素下标，当topPos大于等于10时，说明cnns用于存储Connection对象引用的元素已经耗尽，返回null.

　　main()方法用于测试，当第11次和12次调用makeConnectionManager()方法时，由于元素耗尽，不会得到一个有效的Connection对象引用。

 

运行输出：

Connection 1 done

Connection 2 done

Connection 3 done

Connection 4 done

Connection 5 done

Connection 6 done

Connection 7 done

Connection 8 done

Connection 9 done

Connection 10 done

ConnectionManager runs out of objects

ConnectionManager runs out of objects　

 

实现代码：

public class TestMngr {
    public static void main( String[] args ){
        // test the class ConnectionManager's makeConnectionManager method
        for( int i = 0 ; i < 12 ; i++ ){
                Connection ref = ConnectionManager.makeConnectionManager();
                if( ref != null ){
                    System.out.println( "Connection " + ( i + 1 ) + ref.getStatus() );
                }
                // connectionManager can only hold 10 connections , so when i == 10 and i == 11 , it runs out of objects
                else{
                    System.out.println( "ConnectionManager runs out of objects");
                }
        }

    }
}

class ConnectionManager{
    private static Connection[] cnns = new Connection[ 10 ]; // hold 10 connections
    private static int topPos = 0;
    public ConnectionManager(){ }
    
    public static Connection makeConnectionManager(){
        if( topPos < cnns.length){
            cnns[ topPos ] = Connection.creatConnection();
            return cnns[ topPos++ ];
        }
        else{ // ConnectionManager runs out of objects
            return null;
        }
    }
}

class Connection{
    private String flag = " done";
    private Connection() {}
    public String getStatus(){
        return flag;
    }
    public static Connection creatConnection () {
        return new Connection();
    }
}