javafx label doesnt show loop result

Question

i created a program to show the result of gcd(greatest common divider) between 2 integer numbers step by step not just the final result in java fx

here is the controller class for it

package sample;

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Alert;
import javafx.scene.control.Label;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.scene.text.Text;
import javafx.scene.text.TextFlow;
import javafx.stage.Stage;

import javafx.event.ActionEvent;

import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;

public class Controller implements Initializable {
    int q, r1, r2, r3, r4, r;


    private Main main;
    private Stage primaryStage;


    public void setMain(Main main, Stage primaryStage) {
        this.main = main;
        this.primaryStage = primaryStage;
    }

    @FXML
    private Label label;
    @FXML
    private TextFlow tf;
    @FXML
    private TextArea ta;
    @FXML
    private Text t;
    @FXML
    private TextField field;
    @FXML
    private TextField field1;

    @FXML
    private void handleButtonAction(ActionEvent event) {
        String t1 = field.getText();
        String t2 = field1.getText();
        if (t1.isEmpty() || t2.isEmpty()) {
            Alert alert = new Alert(Alert.AlertType.WARNING);
            alert.setTitle("Warning");
            alert.setHeaderText("Enter Values");
            alert.setContentText("you have to enter Integer Numbers");
            alert.showAndWait();

        } else {
            try {
                r1 = Integer.parseInt(t1);
                r2 = Integer.parseInt(t2);
                if (r1 < r2) {

                    r3 = r2;
                    r4 = r1;
                    r = r3 % r4;
                    q = r3 / r4;
                    String t = ("r1=" + r3 + "     " + "r2=" + r4 + "       " + "q=" + q + "      " + "r=" + r);
                    String t6 = new String();
                    while (r != 0) {


                        r3 = r4;
                        r4 = r;
                        r = r3 % r4;
                        q = r3 / r4;
                        t6 = "r1=" + r3 + "     " + "r2=" + r4 + "       " + "q=" + q + "      " + "r=" + r;
                        System.out.println(t6);

                    }
                    String t7 = ("gcd=" + r4);
                    label.setText(t + "\n" + t6 + "\n" + t7 + "\n");
                    label.setWrapText(true);
                } else {
                    r = r1 % r2;
                    q = r1 / r2;
                    String t3 = ("r1=" + r1 + "     " + "r2=" + r2 + "       " + "q=" + q + "      " + "r=" + r);
                    String t4 = new String();
                    //this part of code
                    while (r != 0) {


                        r1 = r2;
                        r2 = r;
                        r = r1 % r2;
                        q = r1 / r2;
                        t4 = ("r1=" + r1 + "     " + "r2=" + r2 + "       " + "q=" + q + "      " + "r=" + r);

                    }
                    String t5 = ("gcd=" + r2);
                    label.setText(t3 + "\n" + t4 + "\n" + t5 + "\n");



                }
            } catch (Exception e) {
                Alert alert = new Alert(Alert.AlertType.WARNING);
                alert.setTitle("Warning");
                alert.setHeaderText("Values Error");
                alert.setContentText("you can only enter Integer Numbers");
                alert.showAndWait();

            }
            field.clear();
            field1.clear();
        }

    }



    public void close(){
        primaryStage.close();
    }
    @Override
    public void initialize(URL url, ResourceBundle rb){}
    public void changeWindow(){
         main.secondWindow();
    }

}

now here is the result when i enter for example 26 15 here is the result

r1=26     r2=15       q=1      r=11
r1=3     r2=1       q=3      r=0
gcd=1

but the result should be like this as is it apear in the terminal

r1=26     r2=15       q=1      r=11
r1=15     r2=11       q=1      r=4
r1=11     r2=4       q=2      r=3
r1=4     r2=3       q=1      r=1
r1=3     r2=1       q=3      r=0
1

so as i said why the label only show the final result of loop not the whole loop like the terminal show it

Answer 1

If you want to include every step in the Label, you need to add something to the final result for every loop iteration. You do not do something like this. I recommend using a StringBuilder for this purpose:

if (r1 > r2) {
     int t = r1;
     r1 = r2;
     r2 = t;
}
StringBuilder sb = new StringBuilder();
while (r1 > 0) {
    int temp = r2 % r1;
    sb.append("r1=").append(r2).append("     r2=").append(r1).append("       q=").append(r2/r1).append("      r=").append(temp).append('\n');
    r2 = r1;
    r1 = temp;
}
sb.append("gcd=").append(r2);
label.setText(sb.toString());

Answer 2

The problem is that your logic runs withing the Event Dispatch Thread (EDT). Asl long as your logic runs the EDT cannot update the screen.

You need to move your logic into a separate Threat that calls the setText() method within Platform.runLater()