I'm a newbie in Java and I have a file where every first line is the title of every second. For example the text file looks like this:

John Holm

blue

Anna Karina

orange

etc...

where every first line is the name of a person and every second is their favourite colour. Now I would like to use the information to for example find what is for example John Holm's favourite colour or change his favourite colour to green instead. How do I best access the data?

I tried with scanner to see all the lines where blue reoccurs, but I cannot get the code to write the previous line.

Should I split the text file into a table with name and favColour as columns or is there a way to assign the previous line to the next line as a name in Java? I also thought of splitting the file every second line. However, I am unsure which solution would be most efficient. Would be very thankful for some insights!

CodePudding user response：

I think a solution would be to create an object containing the properties of your characters (their name and their favourite colour). So, you can create a class named like how you want to name your object (let's call it Person), and set the name and the favourite colour as attribute of your Person object:

public class Person {

private String name;
private String favColour;

    public Person(String name, String favColour) { // Constructor of your object
        this.name = name; // Setting name
        this.favColour = favColour; // Setting favourite colour
    }

}

Now, create a main method to read your file, store the values into two lists, one containing the names, the other the colours, and then creating as many Person objects as you need:

public class Main {

public static void main(String[] args) throws IOException {
    
        File file = new File("src/wherever you stored it"); // Enter the file path as a String here
        Scanner scanner = new Scanner(file); // Create a scanner that will read your file
        List<String> names = new ArrayList<>(); // List that will contain the names read from the scanner 
        List<String> colours = new ArrayList<>(); // By the way don't forget to import *java.util.List* and *java.util.ArrayList* if your IDE doesn't do it automatically
        int index = 0; // The index that'll know whether you store a name or a colour
        try {
            while(scanner.hasNext()) { // While the scanner still reads something from the file
                if(index%2==0) { // If the index is even
                    names.add(scanner.next()); // Add the line to the names list
                    index  ;
                } else {
                    colours.add(scanner.next()); // Else add it to the colours list
                    index  ;
                }
            }
        } catch (Exception e) { // Don't forget to import *java.io.IOException*
            System.err.println("Error: "   e.getMessage()); // You can write a custom message that will appear in your console if there's an error, e.g. if the program can't find your file
        }
        scanner.close(); // Close your scanner
        // Now you can create a new Person object
        Person p1 = new Person(names.get(0), colours.get(0)); // Create a Person object called p1, with the first element (index 0) of names and colours lists as attributes
        System.out.println(p1); // Print your Person
    }

}

Almost done, the last line must print some weird string. If you want to print your Person properly, you have to override the toString() method of your object:

// In the Person class:
@Override
public String toString() {
    return "Name: "   this.name   "\nFavourite colour: "   this.favColour;
}

Now try again and you'll see the console prints properly what you want to see. In the case of the example you gave, your console should print:

Name: John Holm

Favourite colour: blue

You can create as many Person objects as you want, and maybe store them into a list as well. Feel free to ask anything you didn't understand or think is wrong :)

CodePudding user response：

1. Split into lines (how to)
2. Run a for-loop over the lines advancing 2 each iteration.
3. For each iteration of the loop, read the current line (name) and the next (color), and insert into a hashmap as key-value.
4. Look up a person from the map as needed.

Alternatively, read the files two lines at a time and create the map incrementally.

I’m not going to provide code because:

1. Each of these steps can be found on Google/Stackoverflow.
2. The best way to learn is by writing code yourself.