如何在 Java 中以双精度形式返回数组的元素？

Question

I keep receiving an error in the below codetelling me that the type must be an array but its returning a double for "total[agentnumber]" in the print statement. Can anyone explain this and how I might solve it in this context?

My goal: Write code where I input the number of periods, interest rates, and number of agents (where each agent's is assigned a principal equal to its agent number ie agent 1 receive 100, agent 2 receives 200, etc.) and print the balances of each agent. I want to do this in a loop rather than use the compound interest formula because I am trying to learn how to use Java.

Other issue: This is a bit crazily set up because I do not know how to return the results of the for loops. Where should I place "return" and what should I be returning, supposing that I am interested in ultimately printing the equivalent of agent[agentnumber].money for each of the agents.

public class Person{

    public double money; // initialize

    Person(double cash){
        money = cash;
    }
}

public class Bank {

    public static double bank(double rate, double periods, int agents){
        Person[] agent = new Person[agents];
        double total;

        for( int agentnumber = 0; agentnumber < agents; agentnumber++) {
           agent[agentnumber] = new Person((agentnumber+1)*100); // assign starting incomes and instantiate players

            for(int months = 0; months < periods; months++){
                agent[agentnumber].money = agent[agentnumber].money*(1.0 + rate);
                total = agent[agentnumber].money;
                System.out.println("The total balance of player " + agentnumber + " is " + total[agentnumber]);
            }
        }
    }

    public static void main(String[] args) {
        bank(0.05,120,3);
    }
}

Answer 1

total是一个双total[agentnumber] ，所以只需打印total而不是total[agentnumber]

Answer 2

I keep receiving an error in the below code telling me that the type must be an array but its returning a double for "total[agentnumber]" in the print statement. Can anyone explain this and how I might solve it in this context?

You get this error message because total is a double, not an array. In order to use [] the type must be an array. The solution is to print total instead of total[agentnumber] .

Where should I place "return" and what should I be returning, supposing that I am interested in ultimately printing the equivalent of agent[agentnumber].money for each of the agents.

As your program is written right now, you'll get an error because you have declared that bank() will return a double, but you have no return statement in bank() . It's unclear why you'd want to return anything from bank() . You probably want to change

public static double bank(double rate, double periods, int agents)

to

public static void bank(double rate, double periods, int agents)

and then you don't need to return anything.

Answer 3

What and where should I be returning?

You seem to just want to print out the values of an array, so nothing needs returned. In that case, you could make the method have a void return type. It also isn't really clear why you needed the array because the local agents variable isn't needed by the main method, so if you did want the array, you should return Person[] instead of double ...

You could also clean up the code like so.

public class Bank {

    public static Person[] bank(double rate, double periods, int agents){
        Person[] agent = new Person[agents];

        for( int agentnumber = 0; agentnumber < agents; agentnumber++) {
           Person p = new Person((agentnumber+1)*100); // assign starting incomes and instantiate players

            for(int months = 0; months < periods; months++){
                p.money = p.money*(1.0 + rate);
                System.out.printf("The total balance of player %d at month %d is %.2f\n", agentnumber, months, p.money);
            }

            agent[agentnumber] = p;
        }

        return agent;
    }

    public static void main(String[] args) {
        Person[] agents = bank(0.05,120,3);
    }
}

Answer 4

I've had a go at rewriting your code above and ensured it compiles. There are a few best practice things I would change if this wasn't just a demonstration which I've added in comments

public class Bank {

    public static void main(String[] args) {
        Bank bank = new Bank(0.05,120,3);
    }

    // For readability and simplification I would make this public and
    // move it into it's own file called Person.java 
    private class Person {
        public double money;

        Person(double cash){
            money = cash;
        }
    }

    public Bank(double rate, double periods, int numberOfAgents) {
        Person[] agent = new Person[numberOfAgents];

        // Typical java convention is to use camel case so
        // agentnumber would become agentNumber
        for( int agentnumber = 0; agentnumber < numberOfAgents; agentnumber++) {
            agent[agentnumber] = new Person((agentnumber+1)*100);

            for(int months = 0; months < periods; months++){
                agent[agentnumber].money = agent[agentnumber].money*(1.0 + rate);
            }
            System.out.println("The total balance of player " + agentnumber + " is " + agent [agentnumber].money);
        }
    }
}