hypotenusecalculator.java

来自「32个java程序源代码」· Java 代码 · 共 149 行

// Tutorial 12: HypotenuseCalculator.java
// This program finds and displays hypotenuse of a triangle
// whose sides are entered by the user.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;

public class HypotenuseCalculator extends JFrame
{
   // JLabel and JTextField for length of side A
   private JLabel lengthSideAJLabel;
   private JTextField lengthSideAJTextField;

   // JLabel and JTextField for length of side B
   private JLabel lengthSideBJLabel;
   private JTextField lengthSideBJTextField;

   // JLabel and JTextField for hypotenuse
   private JLabel lengthHypotenuseJLabel;
   private JTextField lengthHypotenuseJTextField;

   // JButton to initiate calculation of hypotenuse
   private JButton calculateJButton;
   
   // no-argument constructor
   public HypotenuseCalculator()
   {
      createUserInterface();
   }
   
   // create and position GUI components; register event handlers
   private void createUserInterface()
   {
      // get content pane for attaching GUI components
      Container contentPane = getContentPane();

      // enable explicit positioning of GUI components
      contentPane.setLayout( null );
      
      // set up lengthSideAJLabel
      lengthSideAJLabel = new JLabel();
      lengthSideAJLabel.setBounds( 16, 13, 96, 21 );
      lengthSideAJLabel.setText( "Length of side A:" );
      contentPane.add( lengthSideAJLabel );
      
      // set up lengthSideAJTextField
      lengthSideAJTextField = new JTextField();
      lengthSideAJTextField.setBounds( 150, 13, 90, 21 ); 
      lengthSideAJTextField.setHorizontalAlignment(
         JTextField.RIGHT );
      contentPane.add( lengthSideAJTextField );
      
      // set up lengthSideBJLabel
      lengthSideBJLabel = new JLabel();
      lengthSideBJLabel.setBounds( 16, 45, 96, 21 );
      lengthSideBJLabel.setText( "Length of side B:" );
      contentPane.add( lengthSideBJLabel );
      
      // set up lengthSideBJTextField
      lengthSideBJTextField = new JTextField();
      lengthSideBJTextField.setBounds( 150, 45, 90, 21 );
      lengthSideBJTextField.setHorizontalAlignment(
         JTextField.RIGHT );
      contentPane.add( lengthSideBJTextField );
      
      // set up lengthHypotenuseJLabel
      lengthHypotenuseJLabel = new JLabel();
      lengthHypotenuseJLabel.setBounds( 16, 89, 130, 21 );
      lengthHypotenuseJLabel.setText( "Length of hypotenuse:" );
      contentPane.add( lengthHypotenuseJLabel );
      
      // set up lengthHypotenuseJTextField
      lengthHypotenuseJTextField = new JTextField();
      lengthHypotenuseJTextField.setBounds( 150, 89, 90, 21 );
      lengthHypotenuseJTextField.setHorizontalAlignment(
         JTextField.CENTER );
      lengthHypotenuseJTextField.setEditable( false );
      contentPane.add( lengthHypotenuseJTextField );
      
      // set up calculateJButton
      calculateJButton = new JButton();
      calculateJButton.setBounds( 150, 121, 90, 23 );
      calculateJButton.setText( "Calculate" );
      contentPane.add( calculateJButton );
      calculateJButton.addActionListener( 
      
         new ActionListener() // anonymous inner class
         {
            // event handler called when calculateJButton is pressed
            public void actionPerformed( ActionEvent event )
            {
               calculateJButtonActionPerformed( event );
            }
            
         } // end anonymous inner class
         
      ); // end call to addActionListener
      
      // set properties of application's window
      setTitle( "Hypotenuse Calculator" ); // set title bar string
      setSize( 262, 182 );                 // set window size
      setVisible( true );                  // display window
      
   } // end method createUserInterface
   
   // calculate and display hypotenuse length
   private void calculateJButtonActionPerformed( ActionEvent event )
   {
      // get input from JTextFields
	  double sideA = Double.parseDouble(
         lengthSideAJTextField.getText() );
	  double sideB = Double.parseDouble(
         lengthSideBJTextField.getText() );
      
      // display error message if user enters invalid input
      if ( sideA <= 0 || sideB <= 0 )
      {
         JOptionPane.showMessageDialog( this,
            "You must enter a non-negative number",
            "Invalid Input Entered", JOptionPane.ERROR_MESSAGE );
      }
      
   } // end method calculateJButtonActionPerformed
   
   // main method
   public static void main( String[] args )
   {
      HypotenuseCalculator application = new HypotenuseCalculator();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

   } // end method main
   
} // end class HypotenuseCalculator

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