display data java from arraylist in column

I would like to know how am I supposed to get the elements from a arraylist in a column(under each other) like this:

BMI:   Length:   gewicht:
1.69       30     24.25
2.58       55     28.25

This is my code:

 @Override
    public String toString() {
        return String.format("%-17.1f%-15.2f%.2f",lengte, gewicht,bmi);        
        
    }


    public static void main(String[]args){
        ArrayList<BMICalculator> bmilist = new ArrayList<>();
JOptionPane.showMessageDialog(null, String.format("length:%-9sgewicht:%-8sbmi:","","") );

        do {
            double lengte = getLength("Geef de lengte in Meters:");
            double gewicht = getGewicht("Geef het gewicht in Kg:");
            BMICalculator bmi = new BMICalculator(lengte, gewicht);
            bmi.setBmi(bmi.calculateBMI());
            bmilist.add(bmi);           
            
            JOptionPane.showMessageDialog(null, String.format("%s", bmi.toString()));
        } while(getUserAnswer() == 'J');

        JOptionPane.showMessageDialog(null,  String.format("%s", bmilist.toString()));
        System.out.println(bmilist);

    }

This code gives me this:
length: gewicht: Bmi:
1,7 80,00 28,01, length: gewicht: bmi:
1,6 55,00 22,03

I dont want that length, gewicht and bmi keeps repeating...
help!!!

Your header and data are merged together in that String.format mask. That's why the header keeps repeating.
You'll need to separate them. So use String.format("length:%-9sgewicht:%-8sbmi:","","") to print the header once, before the loop. And for each line of data use String.format("%-17.1f%-15.2f%.2f",lengte, gewicht,bmi). That way I think you will be fine.

But, if what you want is the whole text into the same pane, it would be something like this:

public static void main(String[] args) {
    StringBuilder sb = new StringBuilder();
    ArrayList<BMICalculator> bmilist = new ArrayList<>();
    
    sb.append(String.format("length:%-9sgewicht:%-8sbmi:\n", "", ""));

    do {
        double lengte = getLength("Geef de lengte in Meters:");
        double gewicht = getGewicht("Geef het gewicht in Kg:");
        BMICalculator bmi = new BMICalculator(lengte, gewicht);
        bmi.setBmi(bmi.calculateBMI());
        bmilist.add(bmi);

    } while (getUserAnswer() == 'J');
    
    for (BMICalculator item : bmilist) {
        sb.append( item.toString() );
    }
    
    JOptionPane.showMessageDialog(null, sb.toString());
    
    System.out.println(bmilist);
}

import java.util.*;
public class Main {
static class Friend {
String name;
int age;
String phone;
public Friend(String name, int age, String phone) {
this.name = name;
this.age = age;
this.phone = phone;
}
@Override
public String toString() {
return String.format("%-15s %-4s %10s", name, "" + age, phone);
}
}
public static void main(String[] args) {
ArrayList<Friend> friends = new ArrayList();
friends.add(new Friend("F11", 12, "phone11"));
friends.add(new Friend("F21", 21, "phone21"));
friends.add(new Friend("F321", 123, "phone321"));
printFriends(friends);
}
private static void printFriends(ArrayList<Friend> friends) {
printHeader() ;
friends.forEach(friend -> System.out.println(friend.toString()));
}
private static void printHeader() {
System.out.println(String.format("%-15s %-4s %10s","Name","Age", "Phone"));
}
}

Output:
Name            Age       Phone
F11             12      phone11
F21             21      phone21
F321            123    phone321

Play with String format and spacing to get desired column spacing.