Question

/*
 * Notes here
 */
package billboardsign;

/**
 *
 * @author John Parada
 */
import java.util.ArrayList;
public class Billboard 
{
    private String text;
    private ArrayList<String> messages = new ArrayList<String>();

    public Billboard()

    {
        messages.add("Happy New Year");
        messages.add("Happy Holidays");
        messages.add("Team Pizza");
        messages.add("Game On");
        messages.add("Let's Go Team");
    }

public ArrayList<String> getMessages()
{
    return messages;
}
public void setMessages(String msg)
{
    messages.add(msg);
}
public boolean isEmpty()
{
    return text == null || text.isEmpty();
}
public String substring(int begin, int end)
{
    if (begin >= 0 && end < text.length())
    {
        return text.substring(begin, end);
    }
    else
        return null;
}



//add the method Reverse here    
// THIS CODE IS NO GOOD!for (int count = text.length() - 1; count >= 0; count-- )
        //FOLLOW UP LINE System.out.printf( "%s ", text.charAt( count ) );
public String reverse()
{
    if (isEmpty())
        return null;
    else
    {
        char[] chars = text.toCharArray();

        //create antoher arrayList
        char[] reverse = new char[chars.length];

        for (int i = chars.length - 1, j = 0; i < 0; i--, j++)
        {
        reverse[j] = chars[i];
        }
    return new String(reverse);

    }
}

//add the method Replace string here
public String replace(char oldChar, char newChar)
{
return text.replace(oldChar, newChar);
}

//add the method displayInfo here
public void displayInfo()
{
    System.out.printf("\n%s\nMessage", messages);

}


}







/*
 * Notes on the Billboard Project
 */
package billboardsign;

/**
 *
 * @author John Parada
 */
import java.util.Scanner;

public class BillboardSign 
{

/**
 * @param args the command line arguments
 */
public static void main(String[] args) 
{

    Billboard newBillboard = new Billboard(); //default constructor


    //Menu 
    int choose_again = 1;
    int choiceNumber;
    Scanner newInput = new Scanner(System.in);
    while (choose_again > 0 )
    {
        //list options to user
        System.out.println ("\nPlease choose a number between 1 and 6 to choose an\n"
            + "option for the Messages Board to display: "
            + "\n1) Display Default Message 1"
            + "\n2) Display Default Message 2"
            + "\n3) Display Default Message 3"
            + "\n4) Display Default Message 4"
            + "\n5) Display Default Message 5"
            + "\n6) Enter a New Message"
            + "\n7) Reverse a Message"
            + "\n8) Replace a Message - Substring"
            + "\n9)  Exit Program");

        //get the user to input a selection 
        System.out.print ("\nPlease Enter Your Selection: ");
        choiceNumber = newInput.nextInt();

        //use switch statement to help with thieir choice input
        switch (choiceNumber)
            {   
                case 1:
                    //execute get() and displayInfo() method for default Message 1
                    //newBillboard = Billboard();
                    messages.get(0);
                    displayInfo();
                    break;
                case 2:
                    //execute get() and displayInfo() method for default Message 2
                    newBillboard = Billboard();
                    Billboard = displayInfo();
                    break;
                case 3:
                    //execute get() and displayInfo() method for default Message 3
                    newBillboard = Billboard();
                    Billboard = displayInfo();
                    break;
                case 4:
                    //execute get() and displayInfo() method for default Message 4
                    newBillboard = Billboard();
                    Billboard = displayInfo();
                    break;
                case 5:

                    displayInfo();
                    break;
                case 6:
                    //execute set() and displayInfo() methods to create a new message
                    break;
                case 7:
                    //execute reverse message method 
                    break;
                case 8:
                    //execute Replace message - Substring method
                case 9:
                    //Dispaly to the user that they have chose to exit 
                    System.out.print ("\nYou have chosen to cancel and exit. \n");
                    System.exit(0);
            }




        //prompt user for antother selection? (Contiune=1 and Exit= -1)
        System.out.println();
        System.out.print ("\nIf you would like to select another animal enter 1 or if your are done enter -1: ");
        choose_again = newInput.nextInt();
    }

}

private static void displayInfo() {
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
}

简而言之，当用户选择1时，他或她应该获得ArrayList（0）的第一个元素。当他或她选择2时，他们将获得ArrayList（1）中的第二个元素。我需要调用get方法，并使用Billboard的displayInfo。

提前感谢您提供任何帮助。

此致

John Parada

Answer 1

同样做点什么，

case 1:
   newBillboard.getMessages().get(0);
   ...
case 1:
   newBillboard.getMessages().get(1);
....
And so on.

Answer 2

你的getMessages（）方法返回一个arraylist，所以你应该在你的主类中有一个arraylist变量，如下所示

ArrayList<String> messages = newBillboard.getMessages();

然后像这样调用它

case 1:
                    //execute get() and displayInfo() method for default Message 1
                    //newBillboard = Billboard();
                    System.out.println (messages.get(0));
                    //displayInfo();
                    break;

或者你可以简单地称它为

newBillboard.getMessages.get(0);//here 0 is for first element

并且无需在每种情况下获得班级的对象 displayInfo的需要是什么还不清楚所以，如果你说为什么你补充说我可能会看到它。

从另一个类中的ArrayList获取和设置方法

2 个答案: