将对象值传递给方法

Question

I am trying to make a void method that calculates average, but I would like to pass values to the method from the main method. Here is an example of what I am trying to do:

 public class Plant {

    int leaves;
    int age;
    int sumLeaves;
    double average;

    void averageLeaves() {

        sumLeaves = leaves + leaves; //here is where I need help
        average = (double) sumLeaves / 2;
        System.out.println("The average number of leaves is: " + average);

    }

    public static void main(String[] args) {

        Plant plantA = new Plant();
        plantA.leaves = 5;

        Plant plantB = new Plant();
        plantB.leaves = 3;

        averageLeaves();

    }

The problem I'm having is getting the values of multiple plants into the method. I've tried using .get , loops, static , and many other things and haven't figured it out yet. What I want is to the value of plantA.leaves and plantB.leaves to the method in order to find their sum.

Answer 1

Since you have the averageLeaves() defined in the Plant class, You have to actually invoke the methode from one of the plant instance. Here is how you should do it.

plantA.averageLeaves();

One big mistake you are doing here is,

sumLeaves = leaves + leaves;         

This actually adds the leaves of a specific (one) instance of plants, It is wrong. you have to actually pass the number of leaves from difference instances.

Here is a nicer way to do it using getters & setters. Also it would make much sense to make the averageLeaves() method static. That way you do not need an instance to invoke the method.

    public class Plant {

    int leaves;
    int age;
    //int sumLeaves;  you do not need them now, as the averageLeaves method is static
    //double average;

    static void averageLeaves (int leaves1, int leaves2) {

        int sumLeaves = leaves2 + leaves1;               //here is where I need help
        double average = (double) sumLeaves / 2;
        System.out.println("The average number of leaves is: " + average);
    }

    void setLeaves(int leaves){
        this.leaves = leaves;
    }

    int getLeaves(){
        return this.leaves;
    }
}

    public class Main {

    public static void main(String[] args) {

        Plant plantA = new Plant();
        plantA.setLeaves(5);

        Plant plantB = new Plant();
        plantB.setLeaves(3);

        Plant.averageLeaves(plantA.getLeaves(), plantB.getLeaves());
    }
}

Answer 2

You will have to do it like this:

public class Plant 
{
    int age;
    int sumLeaves;
    double average;

    void averageLeaves (int leaves) 
    {
        sumLeaves = leaves + leaves;               //here is where I need help
        average = (double) sumLeaves / 2;
        System.out.println("The average number of leaves is: " + average);
    }
}

public class Example
{ 
        public static void main(String[] args) 
        {
            Plant plantA = new Plant();
            plantA.leaves = 5;

            Plant plantB = new Plant();
            plantB.leaves = 3;

            plantA.averageLeaves(plantA.leaves);
            plantB.averageLeaves(plantB.leaves);
        }
}

Look that you only have to declare the variables that you want to input into the method (inside the parenthesis) and when you use your method you have to pass the values that the method will use ( in order of declaration in the method ).

I expect it will be helpful for you!

Answer 3

It's a little unclear what you mean. Is the average of the plant itself? The average of the two plants. I'm assuming the latter. Then one way of doing it is to invoke the method as a static member and pass in the leaves as arguments.

public class Plant {

    int leaves;

    static void averageLeaves (int leaves1, int leaves2) {
        int sumLeaves = leaves1 + leaves2;    //here is where I need help
        double average = (double) sumLeaves / 2;
        System.out.println("The average number of leaves is: " + average);
    }

    public static void main(String[] args) {

        Plant plantA = new Plant();
        plantA.leaves = 5;

        Plant plantB = new Plant();
        plantB.leaves = 3;

        Plant.averageLeaves(plantA.leaves, plantB.leaves);

}

Answer 4

Here is a simple version that allows you to pass in a variable number of plants and calculate their average.

public class Plant {
    private int leaves;

    public Plant(int leaves) {
        this.leaves = leaves;
    }

    public int getLeaves() {
        return this.leaves;
    }

    public static void main(String[] args) {
        PrintLeavesAverage(
            new Plant(5),
            new Plant(10),
            new Plant(15),
            new Plant(12)
        );
    }

    private static void PrintLeavesAverage(Plant... plants) {
        int totalLeaves = 0;
        for (Plant p : plants) {
            totalLeaves += p.getLeaves();
        }
        double average = (double)totalLeaves/plants.length;
        System.out.println("The average number of leaves is: " + average);
    }
}

... or if you want to get a bit fancier, and want to try out some of the newer Java 8 features, you can use streams to calculate the average like this:

private static void PrintLeavesAverage(Plant... plants) {
    OptionalDouble average = Arrays.stream(plants).mapToInt(p -> p.leaves).average();

    if (average.isPresent()) {
        System.out.println("The average number of leaves is: " + average.getAsDouble());
    } else {
        System.out.println("No plants, no average");
    }
}