It is a question from a book that I cannot understand but somehow I wanted to know if I have coded it right

Use a single-subscripted array to solve the following problem. A company pays its salesperson on a commission basis. The salespeople receive $200 per week plus 9% of their gross sales for that week. For example, a person grosses $5000 in sales in a week receives $200 plus 9% of $5000 or a total of $650. Write an applet (using an array of counters) that determines how many of the salespeople earned salaries in each of the following ranges ( assume that each salesperson's salary is truncated to an integer amount):

• $200-$299
• $300-$399
• $400-$499
• $500-$599
• $600-$699
• $700-$799
• $800-$899
• $900-$999
• $1000 and over

The applet should use the GUI techniques introduced in Chapter 6. Display the results in JTextArea. Use JTextArea method setText to update the results each value input by the user.

This is the problem, now I wanted to know if I did it right since no one would correct me from the book.

public class ArrayExercise {

    static final int salaryPerWeek = 200;
    static final double commission = 0.09;
    static int[] grossIncome= { 200, 300, 400, 500, 600, 700, 800, 900, 1000 };

    public static void main(String[] args) {
        JFrame frame = new JFrame();

        JTextArea outputArea = new JTextArea();
        outputArea.setText("Salesperson income for the past week :\n");
        frame.add(outputArea);

        for ( int counter = 0; counter < grossIncome.length; counter++) {
            outputArea.append("\nSalesperson[" + counter + "] = " + calculate( grossIncome[ counter ]));
        }

        frame.setLayout(new FlowLayout());
        frame.setVisible(true);
        frame.setSize(300, 300);
    }

    public static double calculate( int salary ) {
        double total = 0;
        total = salary * commission + salaryPerWeek;
        return  total;
    }
}

The output goes like this :

Salesperson[0] = 218.0
Salesperson[1] = 227.0
Salesperson[2] = 236.0
Salesperson[3] = 245.0
Salesperson[4] = 254.0
Salesperson[5] = 263.0
Salesperson[6] = 272.0
Salesperson[7] = 281.0
Salesperson[8] = 290.0

Sorry I am new here and I really wanted to learn Java. Please bear with me.

The problem description gives you a hint:

> (using an array of counters)

Your array is the right size, but it shouldn’t contain money amounts, it should contain counts of people in each salary range.

private int[] countsForEachSalaryRange = new int[9];

• The first element of that array is the number of salespeople who received $200–$299.
• The second element of that array is the number of salespeople who received $300–$399.
• The third element of that array is the number of salespeople who received $400–$499.
• And so on.

A new int[] is automatically filled with zero values when no explicit initialization is done, which is what you want in this case.

Your program should provide a means for the user to enter multiple money amounts. Each amount will be the amount of gross sales made by a salesperson. In the example described by the problem, 5000 would be one such gross sales amount.

One way to do this is to add a JTextField to your JFrame, into which the user can type a gross sales amount. Add an ActionListener to that JTextField which parses the field’s text as an integer.

If the parsing succeeds, you’ll want to analyze the integer value, that is, the gross sales amount.

An easy way to analyze a gross sales amount is simply to calculate the salary from the gross sales, then write a series of if/else statements that check whether the salary is in each of the possible ranges. Each if-statement’s body should increment a different element of countsForEachSalaryRange.

Each time that analysis is done, clear your outputArea and set its text using the current array of counts.

I think you have not correctly understood the question. You are missing an extra input: the list of the sales figures per salesperson. You need an extra input list with salespersons sales and for each revenue calculate the salary and add 1 to the corresponding element in the Salesperson list.

input : 5000
salary: 650
Salesperson[4]= +1

Salesperson[4] represents salaries between 600 and 699. SO you have to add up the number of salaries in each range, not the salary itself.

By the way: there is no problem in learning the java basics with an older version. Nowadays a lot of developers try to write everything with lambda's and streams but it doesn't always help a lot to the readability or maintainability of the code. You will understand the language better if you start with for-loops and if-blocks. Good luck.