Class is not abstract and does not override abstra

Question

import java.awt.*;
import java.awt.event.*;

public class QuadraticSolver extends Frame implements ActionListener, WindowListener
{
private TextField tfX2;
private TextField tfX;
private TextField tfNum;
private TextField tfVal1;
private TextField tfVal2;
private TextField tfRoots;

private Label lblX2;
private Label lblX;
private Label lblNum;
private Label lblVal1;
private Label lblVal2;
private Label lblRoots;

private Button btnCheckRoots;
private Button btnCalc;
private Button btnClear;

double a = 0, b = 0, c = 0;
double Val1 = 0, Val2 = 0, Discriminant = 0;
String StrVal1, StrVal2;

public QuadraticSolver()
{
    Panel panelX2Comp = new Panel(new FlowLayout());
    {
        lblX2 = new Label("Enter Co-Efficient Of X^2:");
        panelX2Comp.add (lblX2);

        tfX2 = new TextField("", 20);
        tfX2.setEditable(true);
        panelX2Comp.add(tfX2);
    }

    Panel panelXComp = new Panel(new FlowLayout());
    {
        lblX = new Label("Enter Co-Efficient Of X:");
        panelXComp.add(lblX);

        tfX = new TextField("", 20);
        tfX.setEditable(true);
        panelXComp.add(tfX);
    }

    Panel panelNumComp = new Panel(new FlowLayout());
    {
        lblNum = new Label("Enter Number:");
        panelNumComp.add(lblNum);

        tfNum = new TextField("", 20);
        tfNum.setEditable(true);
        panelNumComp.add(tfNum);
    }

    Panel panelButtons = new Panel(new FlowLayout());
    {
        btnCalc = new Button("Calculate");
        btnCalc.setEnabled(false);
        panelButtons.add(btnCalc);
        {
            btnCalc.addActionListener(new ActionListener()
            {
                 @Override
                public void actionPerformed(ActionEvent e)
                {
                    a = Double.parseDouble(tfX2.getText());
                    b = Double.parseDouble(tfX.getText());
                    c = Double.parseDouble(tfNum.getText());

                    Val1 = (-b + Math.sqrt(Discriminant)) / (2 * a);
                    Val2 = (-b - Math.sqrt(Discriminant)) / (2 * a);

                    StrVal1 = String.valueOf(Val1);
                    StrVal2 = String.valueOf(Val2);

                    tfVal1.setText(StrVal1);
                    tfVal2.setText(StrVal2);

                    tfX2.setText("");
                    tfX.setText("");
                    tfNum.setText("");

                    btnCalc.setEnabled(false);
                }
            }
            );
        }

        btnCheckRoots = new Button("Nature Of Roots");
        panelButtons.add(btnCheckRoots);
        {
            btnCheckRoots.addActionListener(new ActionListener()
            {
                 @Override
                public void actionPerformed(ActionEvent e)
                {
                    a = Double.parseDouble(tfX2.getText());
                    b = Double.parseDouble(tfX.getText());
                    c = Double.parseDouble(tfNum.getText());

                    Discriminant = (b*b) - (4*(a*c));

                    if (Discriminant == 0)
                    {
                        tfRoots.setText("Equal");
                        btnCalc.setEnabled(true);
                    }
                    else if (Discriminant < 0)
                    {
                        tfRoots.setText("Imaginary");
                    }
                    else
                    {
                        tfRoots.setText("Real, Distinct");
                        btnCalc.setEnabled(true);
                    }


                }

            }
            );
        }

        btnClear = new Button("Clear");
        panelButtons.add(btnClear);
        {
            btnClear.addActionListener(new ActionListener() 
            {

                 @Override
                public void actionPerformed(ActionEvent e)
                {
                    a = 0; b = 0; c = 0;
                    Val1 = 0; Val2 = 0; Discriminant = 0;


                    tfX2.setText("");
                    tfX.setText("");
                    tfNum.setText("");
                    tfVal1.setText("");
                    tfVal2.setText("");
                    tfRoots.setText("");
                }
            }
            );
        }


    }   

    Panel panelRoots = new Panel(new FlowLayout());
    {
        lblRoots = new Label ("Nature Of Roots:");
        panelRoots.add(lblRoots);

        tfRoots = new TextField("", 20);
        tfRoots.setEditable(false);
        panelRoots.add(tfRoots);
    }

    Panel panelValues = new Panel(new FlowLayout());
    {
        lblVal1 = new Label("First Value:");
        panelValues.add(lblVal1);

        tfVal1 = new TextField("", 10);
        tfVal1.setEditable(false);
        panelValues.add(tfVal1);

        lblVal2 = new Label("Second Value:");
        panelValues.add(lblVal2);

        tfVal2 = new TextField("", 10);
        tfVal2.setEditable(false);
        panelValues.add(tfVal2);

    }

    setLayout(new FlowLayout());  // "this" Frame sets to BorderLayout
    add(panelX2Comp);
    add(panelXComp);
    add(panelNumComp);
    add(panelButtons);
    add(panelRoots);
    add(panelValues);

    setTitle("Matrix Multiplier"); // "this" Frame sets title
    setSize(400, 200);        // "this" Frame sets initial size
    setVisible(true);    


    addWindowListener(this);
}

 @Override
public void windowClosing(WindowEvent e) 
{
    System.exit(0);  // Terminate the program
}
 @Override
 public void windowOpened(WindowEvent e) { }
 @Override
 public void windowClosed(WindowEvent e) { }
 @Override
 public void windowIconified(WindowEvent e) { }
 @Override
 public void windowDeiconified(WindowEvent e) { }
 @Override
 public void windowActivated(WindowEvent e) { }
 @Override
 public void windowDeactivated(WindowEvent e) { }


public static void main(String args[])
{
    new QuadraticSolver();
}
}

So this is my code. it give me an error saying "QuadraticSolver.java:4: error: QuadraticSolver is not abstract and does not override abstract method actionPerformed(ActionEvent) in ActionListener public class QuadraticSolver extends Frame implements ActionListener, WindowListener"

I have no idea what to do. I tried adding @Override before all ActionListener events, Still doesn't work.

Answer 1

I Noticed that you implement actionperformed for your actionlistener of your button.When you declare that you are going to implement an interface, you need a separate actionperformed method in your class. like

public class QuadraticSolver implements ActionListener{
@Override 
public void  actionPerformed(ActionEvent){}
}

Answer 2

Since QuadraticSolver implements ActionListener, it should implement actionPerformed.

You implemented that method in an anonymous class.

To solve it, either add an implementation of actionPerformed to QuadraticSolver or don't require QuadraticSolver to implement that interface.

Answer 3

As you have used ActionListener so you are bound to override its method which is actionPerformed(ActionEvent ae) otherwise it will give this error.