Re: Partly off-topic: Q on inner classes/ActionListener

[Ramakanth Padmanabhan Sengamedu]

The method in the class implementing ActionListener should be
actionPerformed and not ActionPerformed. ( Note the case of the method name)

-----Original Message-----
From: RVASUDEV [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, October 26, 1999 6:50 PM
To: [EMAIL PROTECTED]
Subject: Partly off-topic: Q on inner classes/ActionListener


Hi

[Platform: Win NT 4.0 SP3, Sun JDK 1.2.2]

While compiling a java application, I get some
errors. App and err details below. Any suggestions
appreciated. [The program is a simple one to
encode/decode a file, the encode/decode logic
hasn't been added yet]

TIA
Vasudev

The application :

-------------------------------------------------
// Codec1.java

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

public class Codec1 extends Frame {

        /** initialize fields */
        Label inFileLabel = new Label("Input file name");
        TextField inFileName = new TextField(64);
        Label outFileLabel = new Label("Output file name");
        TextField outFileName = new TextField(64);
        Button encodeBtn = new Button("Encode");
        Button decodeBtn = new Button("Decode");
        Button exitBtn = new Button("Exit");
        TextField status = new TextField(64);
        FileInputStream fis;
        BufferedInputStream bis;
        DataInputStream dis;
        FileOutputStream fos;
        BufferedOutputStream bos;
        DataOutputStream dos;

        /** main - just creates a new Codec1 object */
        public static void main(String[] args) {
                new Codec1();
        }

        /* no-arg constructor */
        public Codec1() {

                super("Codec1");

                // setup GUI
                setLayout(new FlowLayout());
                add(inFileLabel);
                add(inFileName);
                add(outFileLabel);
                add(outFileName);
                add(encodeBtn);
                add(decodeBtn);
                add(exitBtn);
                add(status);

                // add listeners
                encodeBtn.addActionListener(new EncBtnAL());
                decodeBtn.addActionListener(new DecBtnAL());
                exitBtn.addActionListener(new ExiBtnAL());

                enableButtons();
                this.setSize(400, 500);
                this.setVisible(true);
                this.show();

        }

        /** listener for Encode Button */
        public class EncBtnAL implements ActionListener {
                public void ActionPerformed(ActionEvent ae) {
                        disableButtons();
                        status.setText("Encoding...please wait");
                        encode( inFileName.getText().trim(),
                                outFileName.getText().trim() );
                        enableButtons();
                }
        }

        /** listener for Decode Button */
        public class DecBtnAL implements ActionListener {
        public void ActionPerformed(ActionEvent ae) {
                //disableButtons();
                status.setText("Not implemented yet");
                // decode(inFileName.getText(),
                        //outFileName.getText());
                        //enableButtons();
        }
    }

        /** listener for Encode Button */
        public class ExiBtnAL implements ActionListener {
                public void actionPerformed(ActionEvent ae) {
                System.out.println("Exiting...");
                sleep(1);
                System.exit(0);
        }
        }

        public void encode(String inFileName, String outFileName) {
                try {
                        fis = new FileInputStream(inFileName);
                        bis = new BufferedInputStream(fis);
                        dis = new DataInputStream(bis);
                        fos = new FileOutputStream(outFileName);
                        bos = new BufferedOutputStream(fos);
                        dos = new DataOutputStream(bos);
                        char c;
                        while ((c = dis.readChar()) != -1) {
                                //c = c ^ c;
                                dos.writeChar((int) c);
                        }
                        status.setText("Encoding complete");
                        sleep(1);
                }
                catch(IOException ioe) {
                        System.out.println("IO error: " + ioe);
                        status.setText("Encode failed");
                        sleep(1);
                }
                finally {
                        try {
                                dis.close(); bis.close(); fis.close();
                                dos.close(); bos.close(); fos.close();
                        }
                        catch(IOException ioe) {
                                System.out.println("IO error: " + ioe);
                                status.setText("Close(s) failed");
                                sleep(1);
                        }
                }
        }

        public void disableButtons() {
                encodeBtn.setEnabled(false);
                decodeBtn.setEnabled(false);
                exitBtn.setEnabled(false);
        }

        public void enableButtons() {
                encodeBtn.setEnabled(true);
                decodeBtn.setEnabled(true);
                exitBtn.setEnabled(true);
        }

        public void sleep(int seconds) {
                try {
                        Thread.sleep(seconds * 1000);
                }
                catch(InterruptedException ie)
                {
                }
        }
}
-------------------------------------------------


The errors :

C:> javac Codec1.java 2>e
C:> type e

Codec1.java:47: inner class Codec1. EncBtnAL is an abstract class. It can't
be instantiated.
                encodeBtn.addActionListener(new EncBtnAL());
                                            ^
Codec1.java:48: inner class Codec1. DecBtnAL is an abstract class. It can't
be instantiated.
                decodeBtn.addActionListener(new DecBtnAL());
                                            ^
Codec1.java:59: inner class Codec1. EncBtnAL must be declared abstract. It
does not define void actionPerformed(java.awt.event.ActionEvent) from
interface java.awt.event.ActionListener.
        public class EncBtnAL implements ActionListener {
                     ^
Codec1.java:70: inner class Codec1. DecBtnAL must be declared abstract. It
does not define void actionPerformed(java.awt.event.ActionEvent) from
interface java.awt.event.ActionListener.
        public class DecBtnAL implements ActionListener {
                     ^
4 errors

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