使用对象数组/对象数组查找平均值

Question

this is such a simple problem but for some reason, I cant wrap my head around Array of Objects or Object Arrays. All I have to do is take in 5 user inputs, and create a class called Height, create object array and store user inputs into obj array and print the average. I'm kinda stuck.

class Height{
    int total=0;
    int count=0;
    public Height(int y) {
        total=total+y;
        count++;
    }
    public void print() {
        System.out.print("The average is: "+total/count);
    }
}

public class ObjectArray {
    public static void main(String[] args){
        Scanner s=new Scanner(System.in);
        System.out.println("Enter 5 heights in inches: ");
        int[] x=new int[5];
        int total=0;
        for(int i=0;i<x.length;i++) {
            x[i]=s.nextInt();
        }
        Height[] h=new Height[x.length];
        for(int y=0;y<x.length;y++) {
            h[y]=new Height(x[y]);
        }
        h.print();
    }
}

Maybe I'm over complicating it. The problem right now is that I cannot invoke h.print();. I've tried different iterations, ex: taking out the print method and doing all the printing after every iteration.

Answer 1

Your approach is wrong. Your Height class appears to be responsible for the evaluation of the mean value. Hence, you should put all values inside a single Height instance, instead of generating a new instance for each user value.

However, h is an array of Height s object, while print() method is defined on a single Height instance. In order to call such method, you have to access one of the objects contained in h , that is h[0].print() .

Answer 2

I'm assuming that your goal is simply to print the average of all the heights recieved via user input.

Your code in your main method is a tad confusing, so correct me if I'm wrong in any of the examples I give here. You should, instead of creating the x[] array, simply add the user input for the five values to Height.total in a for loop, and increase the Height.count variable by one each loop through. This should look something like this:

for (int i = 1; i <= 5; i++) {
    // System.out.println("Please enter the next height: ");
    Height.total += s.nextDouble();
    Height.count++;
}

Then, you can run Height.print(); .

I would also recommend adding a System.out.print(""); command to let the user know that they should enter the next value. That's the comment I left in the example code I gave above.

Answer 3

You have to design your Height in a way that match your requirement :

• you need different Height with for each one a value
• you need to know how many instances there is

For that, you need a private value, and a static counter :

class Height {

    private int value = 0;

    private static int count = 0;    // static => nb of instances

    public Height(int y) {
        value = y;
        count++;
    }

    public static int averageOf(Height... heights) {
        return Arrays.stream(heights).mapToInt(h -> h.value).sum() / count;
    }
}

To get the average, because it doesn't depend on a particular instance, you can have a static method, that sums all the value of the Height given and divide by the nb of instance

And use like :

public static void main(String[] args) {
    Scanner s = new Scanner(System.in);
    int nb = 5;
    System.out.println("Enter " + nb + " heights in inches: ");

    Height[] heights = new Height[nb];
    for (int i = 0; i < heights.length; i++) {
        heights[i] = new Height(Integer.parseInt(s.nextLine()));
    }

    System.out.println("Average is " + Height.averageOf(heights));
}

Answer 4

class Height{ int total=0; int count=0; public Height(int y) { total=total+y; count++; } public void print() { System.out.print("The average is: "+total/count); } }

you see the constructor ?

Every time you invoke that it will create a new object. and print() can be called on only one Height object.

Rethink about how to create Height object. You don't need an array.

You could do something like below , create a method called update that updates your variables in the class Height . ( Note : think about renaming this class also may be AverageHeight .)

class Height{ int total=0; int count=0; public void update(int y) { total=total+y; count++; } public void print() { System.out.print("The average is: "+total/count); } }

Then in your main() :

Instead of : Height[] h=new Height[x.length]; for(int y=0;y<x.length;y++) { h[y]=new Height(x[y]); } Height[] h=new Height[x.length]; for(int y=0;y<x.length;y++) { h[y]=new Height(x[y]); }

Do this :

Height h=new Height(); for(int y=0;y<x.length;y++) { h.update( x[y] ); } h.print();