将项目添加到ArrayList

Question

I have an array list of Fleets (Each fleet will hold its own list of Trucks).

I have a fleet class with the constructor

public Fleet(String businessName){
    this.businessName = businessName;
    this.fleetList = new ArrayList<Truck>();
}

So:

In my TUI, I have a helper method called createFleet. When the user presses 1 on the menu, it asks for a name of his business, and then makes a fleet named that. That method is:

public static void createFleet(){
    System.out.println("");
    System.out.println("Please enter the name of the fleet.");
    inputText = scan.nextLine();

    fleetCollection.add(new Fleet(inputText));
    printFleets();
    System.out.println("");
    System.out.println("--- Fleet: " + inputText + " added ---");
    System.out.println("");
}

And my problem is that when I add one Fleet, and print the results I get:

Fleet 0: Fleet Number One

But when I add Fleet Number One, then press 1 on the menu again to add ANOTHER fleet (named Fleet Number Two) and print the fleet list, the results are:

Fleet 0: Fleet Number Two
Fleet 1: Fleet Number Two

It seems to be confusing the two...and this further breaks the program when I try to add trucks to the fleet, because It cannot pick the "right" fleet.

Please let me know if you need any other of my code. I just need this to correctly add and print the fleets in the fleet list:

private static ArrayList<Fleet> fleetCollection;

Thank you :) for all the help!

Answer 1

您可能已在Fleet类中将businessName声明为static ，如果是，则将其删除

Answer 2

You need to be clear about use of static

static variable

• It is a variable which belongs to the class and not to object(instance)
• Static variables are initialized only once , at the start of the execution . These variables will be initialized first, before the initialization of any instance variables
• A single copy to be shared by all instances of the class
• A static variable can be accessed directly by the class name and doesn't need any object
• Syntax : <class-name>.<variable-name>

static method

• It is a method which belongs to the class and not to the object(instance)
• A static method can access only static data. It can not access non-static data (instance variables)
• A static method can call only other static methods and can not call a non-static method from it.
• A static method can be accessed directly by the class name and doesn't need any object
• Syntax : <class-name>.<method-name>
• A static method cannot refer to " this " or " super " keywords in anyway

src : http://www.javatutorialhub.com/java-static-variable-methods.html

Answer 3

have you overridden the equals method in Fleet ? if so and it's not correct, it could be the cause of your weird result

Answer 4

I made small modifications to your program to make it simple.

class Fleet{
String businessName;
public Fleet(String businessName)
{ this.businessName = businessName;}
public String getBusinessName()
{
    return businessName;
}
}

public class T {
private static ArrayList<Fleet> fleetCollection = new ArrayList<Fleet>();

    public static void main(String[] args) 
    {
        createFleet("A");
         printFleets();
         createFleet("B");
        printFleets();
    }
     public static void createFleet(String name){
    System.out.println("");
    fleetCollection.add(new Fleet(name));
}
public static void printFleets(){
    Iterator i = fleetCollection.iterator();
    Fleet f;
    while(i.hasNext())
    {
        f = (Fleet)i.next();
        System.out.println(f.getBusinessName());
    }
}

}

It prints as expected.

A

A
B

Check your access modifiers on "businessName" field. It shouldn't be static. Also check printFleets() method.