Constructor trouble shooting

Question

Here is my project:

package myProjects;

import java.awt.GridBagConstraints;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.*;

public class GeometryEquationSolver extends JFrame{

JPanel mainPanel;
JTextField eq1Text, eq2Text;
JButton enterButton, clearTextButton;

public static void main(String[] args) {
    new GeometryEquationSolver();
}
public GeometryEquationSolver(){
    this.setSize(340, 140);
    this.setTitle("Equation Solver");
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    this.setLocationRelativeTo(null);

    mainPanel = new JPanel();
    mainPanel.setLayout(new GridBagLayout());

    addItem(new JLabel("Equation 1"), 0, 0, 1, 1);
    addItem(new JLabel("Equation 2"), 2, 0, 1, 1);

    eq1Text = new JTextField(10);
    addItem(eq1Text, 0, 1, 1, 1);
    eq2Text = new JTextField(10);
    addItem(eq2Text, 2, 1, 1, 1);

    addItem(new JLabel("="), 1, 1, 1, 1); // Just the "=" for looks.

    enterButton = new JButton("Enter");
    enterButton.addActionListener(e->{
        Equation eq1 = new Equation(eq1Text.getText());
    });
    addItem(enterButton, 0, 2, 1, 1);

    clearTextButton = new JButton("Clear");
    clearTextButton.addActionListener(e->{
        eq1Text.setText(null);
        eq2Text.setText(null);
    });
    addItem(clearTextButton, 2, 2, 1, 1);

    this.add(mainPanel);
    this.setVisible(true);
}
private String[] rawData;
private String[] splitEq(String eq){
    rawData = eq.split("");
    return rawData;
}
private void addItem(JComponent c, int x, int y, int width, int height){
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.gridx = x;
    gbc.gridy = y;
    gbc.gridwidth = width;
    gbc.gridheight = height;
    gbc.weightx = 100.0;
    gbc.weighty = 100.0;
    gbc.fill = GridBagConstraints.NONE;

    mainPanel.add(c, gbc);
}
}
class Equation{

public enum opperation {add, sub, mult, div};
public opperation opper;
public String eq;

public Equation(String eq){
    this.eq = eq;
    opper = opperation.add;
    this.Equation(this.eq, opper);
}
 public Equation(String eq, opperation opper){

    }
}

My problem occurs in the class Equation. In the first constructor I have to following line:

this.Equation(this.eq, opper);

And I get this error:

The method Equation(String, Equation.opperation) is undefined for the type Equation

I'm trying to call the constructor after the first one. Does anyone know how to fix this?

Answer 1

The correct syntax would be this(this.eq, opper); . However, as this line must be the first line in your constructor's code, it would become this(eq, opperation.add); .

So your constructor would finally look like this:

public Equation(String eq){
    this(eq, opperation.add);
    this.eq = eq;
    opper = opperation.add;
    //this.Equation(this.eq, opper);
}

If it's absolutely necessary to have some code executed before calling the other constructor, perhaps this answer can help.

Answer 2

If you would like to call a constructor from a constructor, pls refer https://docs.oracle.com/javase/tutorial/java/javaOO/thiskey.html

Here is the code that can work.

public class Equation {

    public static enum opperation {add, sub, mult, div};
    public opperation opper;
    public String eq;

    public Equation(String eq){
        this(eq, opperation.add);
        this.eq = eq;
        opper = opperation.add;
    }
    public Equation(String eq, opperation opper){

    }
}