无法从 static 上下文中引用非静态方法 toString()

Question

Don't want any code, just want some sort of guidance. Would like to keep my academic integrity in tact;)

I keep getting that annoying error. I need to call the toString method for each Room instance. Any suggestions? I would prefer an answer within 2 hours if at all possible.

public class Hotel
{
    //constant
    public static final int NUM_ROOMS = 20;

    //variables
    public Room[] theRoom;
    public String name;
    public int totalDays;
    public double totalRate;
    public int singleCount;
    public int doubleCount;
    public int roomsRented;
    public int NOT_FOUND;

    public Hotel(String newName) {
        name = newName;
        Room[] Rooms = new Room[NUM_ROOMS];
    }

    public double getTotalRentalSales() {
        return totalRate + roomsRented;
    }

    public double getAvgDays() {
        return roomsRented/totalDays;
    }

    public double getAvgRate() {
        return totalRate/roomsRented;
    }

    public int getSingleCount() {
        return singleCount;
    }

    public int getDoubleCount() {
        return doubleCount;
    }

    public String printRentalList() {
        System.out.println("Room Information: " + Room.toString());
    }
}

Answer 1

You shouldn't try to call toString() on a Room class but rather on a Room object . In that method, loop through the array of rooms with a for loop and print the String returned by calling toString() for each Room object held in the array since this is what it looks like your method should do.

For example

System.out.println("All Foos held here include: ");

// using a "for-each" loop, assuming an array called fooArray that holds Foo objects
for (Foo foo: fooArray) {
   System.out.println(foo);
}

You will obviously have to change the types and variable names for your code.

Edit 2: although you will have to use a standard for loop, not a for-each loop, since you won't be looping through the entire array, but rather will quit when roomsRented count is reached.

System.out.println("All Foos held here include: ");

// using standard for loop, assuming an array called fooArray that holds Foo objects
for (int i = 0; i < someMaxNumber; i++) {
   System.out.println(fooArray[i]);
}

Answer 2

System.out.println(Arrays.toString(arr));

In this line when you are writing arrays a dropdown menu will appear, there you will see the default package or the java.util package. You need to select the java.util package and the problem will be solved.

Answer 3

As error is already states, do not call instance method in static context.

Room is a class, not an object. toString is a instance method. So Room.toString() in this case compiler looks for a static method toString. But toString is an instance method so it is causing an issue.

Always remember instance methods are called with the object of the class, not with class itself.

Answer 4

What you're probably doing is calling toString() on the class Room, not an instance of it. For example, instead of writing:

Room.toString()

write:

Room r = new Room()
r.toString()

Answer 5

Look at the following code, you can compile toString with a static variable without a new object, it just throw exception at run time

demo>cat Test.java 
class Water {
  public String toString() {return "whatever";}
}

public class Test { 
  static Water water;
  public static void main(String...args) {
    System.out.println(water.toString());
  }
}

demo>javac Test.java 
demo>java Test
Exception in thread "main" java.lang.NullPointerException
    at Test.main(Test.java:8)