Class is not abstract and does not override abstract method AWT Program

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

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 2

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 3

由于已使用ActionListener，因此必须重写其方法actionPerformed（ActionEvent ae），否则将出现此错误。