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问题:
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()); } }
回答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
回答2:
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.
回答3:
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()
回答4:
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)
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