Java toString() method

Question

public String toString()
        {
        String str;
        str = "The test scores in descending order are \n";

        for(int i = 0; i < data.length; i++)
        {
            str = str + data[i] + " ";
        }
        str = str + "\nThe average is " + mean;
        return str;
        }

This code for java returns scores in descending order for my code. But what throws me off is the way the 'str' is being returned. How I understand this is the return value of 'str' is (str + "\nThe average is " + mean). Because this is my last updated value of 'str', it will update the 'str' to "The test scores in descending order are" First, Second the loop, then last "str + "\nThe average is " + mean". So in the end even though we updated str a few times the actually printed 'str' will only be "str + "\nThe average is " + mean". Please explain why the program actually ends up printing

The test scores in descending order are 70 80.......... (element values)

(And then returns the average mean value info)

Answer 1

Because the command was

str = str + "\nThe average is " + mean;

Which means, append to everything already in str and store the results in str. If it was

str = "\nThe average is " + mean;

it would instead replace everything already in str.