我想创建一个具有3个文本字段和2个按钮的JAVA窗口

Question

I want to create a simple Java window with 3 text fields and 2 buttons. I want the buttons to perform subtraction and division operations taking input from the user. I need help in the actionPerformed method with the if-else conditions. I can't figure out what condition to write in the if-else parentheses.

I wrote the following code:

import java.util.Scanner;
import java.awt.*;
import java.awt.event.*;
class Event extends Frame implements ActionListener
{
 TextField tf, tf1, tf2;
 Event()
 {
  tf=new TextField();
  tf.setBounds(60,50,170,20);
  tf1=new TextField();
  tf1.setBounds(60,70,170,20);
  tf2=new TextField();
  tf2.setBounds(60,90,170,20);
  Button b=new Button("Subtraction");
  b.setBounds(100,120,80,30);
  b.addActionListener(this);
  Button b1=new Button("Division");
  b1.setBounds(100,160,80,30);
  b1.addActionListener(this);
  add(b);
  add(b1);
  add(tf);
  add(tf1);
  add(tf2);
  setSize(300,300);
  setLayout(null);
  setVisible(true);
 }
 public void actionPerformed(ActionEvent e)
 {
  if(ActionListener(Subtraction))
  {
   int a,b,c;
   Scanner sc=new Scanner(System.in);
   a=sc.nextInt();
   tf.setText("Enter first value: "+a);
   b=sc.nextInt();
   tf1.setText("Enter second value: "+b);
   c=b-a;
   tf2.setText("Result is: "+ c);
  }
  else
  {
   int d,f,g;
   Scanner sc= new Scanner(System.in);
   d=sc.nextInt();
   tf.setText("Enter first value: "+d);
   f=sc.nextInt();
   tf1.setText("Enter second value: "+f);
   g=d/f;
   tf2.setText("Result is: "+g);
  }
 }
 public static void main(String args[])
 {
  new Event();
 }
}

Answer 1

You should be checking on ActionEvent which is being passed into your actionPerformed method. The ActionEvent contains information about the source of the action. A possible way to use this would be with an 'action command':

final String subtractionCommand = "Subtraction";

...

Button b=new Button("Subtraction");
b.setActionCommand(subtractionCommand);
b.setBounds(100,120,80,30);
b.addActionListener(this);

...

public void actionPerformed(ActionEvent e)
{
  if(e.getActionCommand().equals(subtractionCommand))
  {
    ...
  }
}

Or by using the getSource() method, this is a bit uglier, but as you'll see it returns you the actual object on which the listener is invoked:

public void actionPerformed(ActionEvent e)
{
  if(((JButton) e.getSource()).getText().equals("Subtraction")) {
  {
    ...
  }
}

As a final suggestion I would say to drop the implementation of ActionListener on your main class and create 2 different listeners for both buttons.This way you can separate the code for each action which is a bit cleaner certainly if you would plan to add additional buttons, or invoke the same action from within other places in your application.

Answer 2

Here is a solution using two different action listeners:

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

public class Event extends Frame {
 TextField tf, tf1, tf2;
 Event()
 {
  tf=new TextField();
  tf.setBounds(60,50,170,20);
  tf1=new TextField();
  tf1.setBounds(60,70,170,20);
  tf2=new TextField();
  tf2.setBounds(60,90,170,20);
  Button b=new Button("Subtraction");
  b.setBounds(100,120,80,30);
  b.addActionListener(new ActionListener()
  { 
  public void actionPerformed(ActionEvent e)
  {
  int num1 = Integer.parseInt(tf.getText());
  int num2 = Integer.parseInt(tf1.getText());

   tf2.setText(Integer.toString(num1 - num2));
  }
   });
  Button b1=new Button("Division");
  b1.setBounds(100,160,80,30);
  b1.addActionListener(new ActionListener()
  {
  public void actionPerformed(ActionEvent e)
  {
  int num1 = Integer.parseInt(tf.getText());
  int num2 = Integer.parseInt(tf1.getText());

   tf2.setText(Integer.toString(num1 / num2));
  }
   });

  add(b);
  add(b1);
  add(tf);
  add(tf1);
  add(tf2);
  setSize(300,300);
  setLayout(null);
  setVisible(true);
 }

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

When you click on subtract it subtracts the numbers in text box 1 and text box 2 and displays the result in text box 3.

When click on divide it divides the numbers.