将方法作为参数从一个类传递给Java中另一个类的构造函数

Question

The question I have is as follows:

I have a particular assignment for a java course, where the instructions for the constructor of the second class are as follows:

Define a constructor, with parameters that pass in the user entered initial position and initial velocity, and use them to:

• Initialize both the initial position constant and the current position data field to the value of the parameter for the initial position.
• Initialize both the initial velocity constant and the current velocity data field to the value of the parameter for the initial velocity.

Now the first class's main method:

Define a main method to:

• Display a description of what the program will do to the user (use the height threshold constant in your description).

• Use the static methods ( which are also required to prompt for and validate input ) to read the initial position and initial velocity values from the user.

• Display a couple of blank lines after reading all of the user input. o Create a new object of the FallingItem class, using the initial position and initial velocity read from the user as arguments for the constructor.

This is how I have this set up so far:

projector class:

      public static void main(String[] args) {

    System.out.println("This program will calculate the position and " 
            + "velocity \n of a falling object until it reaches " 
            + HEIGHT_THRESHOLD + " feet above the ground.");

    initialPosition();

    initialVelocity();

    System.out.println();
    System.out.println();

    FallingItem I = new FallingItem(initialPosition(), initialVelocity());

.... Methods below:

'public static double initialPosition(){
      Scanner input = new Scanner(System.in);
      boolean validated; //validator for while statements
     double startPosition; //variable for initialPosition
     System.out.println("Please enter the intial position from which" +
            " you intend to drop the object." + "this cannot be lower "+
            "than 600 feet.");
    do{


    startPosition = input.nextDouble();
    if (startPosition > HEIGHT_THRESHOLD){
        validated = true;
    }
    else{
        System.out.print("error, value is too low. Try again");
        validated = false;
    }


    }while (validated = false);
   return startPosition;
   }


   public static double initialVelocity(){
   Scanner userInput = new Scanner(System.in);
   double startVelocity;

   System.out.println("\n please enter the initial velocity, in feet per" + 
           " second. \n This value cannot be less than -500");
   startVelocity = userInput.nextDouble();

   if(startVelocity <= FallingItem.TERMINAL_VELOCITY){
       System.out.print("error, this value cannot be less than -500 feet" +
               " per second. Please re-enter the value");
       startVelocity = userInput.nextDouble();


   }

   return startVelocity;'

Before you ask: yes , there needs to be a do-while loop, and yes , the methods need to prompt like that

constructor for item class:

public FallingItem(double initialPosition, double    initialVelocity){

    INITIAL_POSITION = initialPosition; //constant to be filled by user input

    INITIAL_VELOCITY = initialVelocity; //constant to be filled by user input

    currentPosition = initialPosition;

    currentVelocity = initialVelocity;

}

So, in short, I would greatly appreciate any help the community has to offer in finding a way to fulfill the requirements without having the user input prompts duplicate themselves, which is what happens currently, as I am frankly out of ideas.

regards, firemagnet.

Answer 1

I'll hit you up on a few of your convention breaks...

FallingItem I = new FallingItem(initialPosition(), initialVelocity());

Variables in Java are to follow Camel casing while classes follow Pascal casing.

• Camel casing: fallingItem , itemThatIsFalling
• Pascal casing: MyFallingItem , FallingItem , BurgerKingHotdog

Also, your Scanner object keeps being defined locally, or within each method in which you want to only use it once. Instead, try defining it globally (above the main method outside of the main method's brackets). You can then reference it anywhere in your program without having to initialize a new instance of it just to use it once. If you're having difficulty understanding global variables, check this out.

Make sure that you're properly formatting your code as well. The easier you make it to read, the easier it is to detect errors. Clean code just makes everyone's life easier.