classaverage.java

32个java程序源代码

// Exercise 9.11: ClassAverage.java
// Application enables user to have the average of grades calculated.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ClassAverage extends JFrame
{
   // JLabel and JTextArea for list of grades
   private JLabel gradeListJLabel;
   private JTextArea gradeListJTextArea;

   // JButton initiates retrieving grades
   private JButton getGradesJButton;

   // JButton initiates calculating average
   private JButton averageJButton;

   // JLabel and JTextField used to display average
   private JLabel classAverageJLabel;
   private JTextField classAverageJTextField;
   
   private int total = 0; // holds value of the grade total

   // no-argument constructor
   public ClassAverage()
   {
      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 gradeListJLabel
      gradeListJLabel = new JLabel();
      gradeListJLabel.setBounds( 16, 8, 70, 23 );
      gradeListJLabel.setText( "Grade list:" );
      contentPane.add( gradeListJLabel );

      // set up gradeListJTextArea
      gradeListJTextArea = new JTextArea();
      gradeListJTextArea.setBounds( 16, 32, 88, 180 );
      contentPane.add( gradeListJTextArea );

      // set up getGradesJButton
      getGradesJButton = new JButton();
      getGradesJButton.setBounds( 128, 50, 100, 26 );
      getGradesJButton.setText( "Get Grades" );
      contentPane.add( getGradesJButton );
      getGradesJButton.addActionListener(

         new ActionListener() // anonymous inner class
         {
            // event handler called when getGradesJButton is clicked
            public void actionPerformed( ActionEvent event )
            {
               getGradesJButtonActionPerformed( event );
            }

         } // end anonymous inner class

      ); // end call to addActionListener

      // set up averageJButton
      averageJButton = new JButton();
      averageJButton.setBounds( 128, 90, 100, 26 );
      averageJButton.setText( "Average" );
      averageJButton.setEnabled( false );
      contentPane.add( averageJButton );
      averageJButton.addActionListener(

         new ActionListener() // anonymous inner class
         {
            // event handler called when averageJButton is clicked
            public void actionPerformed( ActionEvent event )
            {
               averageJButtonActionPerformed( event );
            }

         } // end anonymous inner class

      ); // end call to addActionListener

      // set up classAverageJLabel
      classAverageJLabel = new JLabel();
      classAverageJLabel.setBounds( 128, 132, 90, 23 );
      classAverageJLabel.setText( "Class average:" );
      contentPane.add( classAverageJLabel );

      // set up classAverageJTextField
      classAverageJTextField = new JTextField();
      classAverageJTextField.setBounds( 128, 156, 100, 21 );
      classAverageJTextField.setEditable( false );
      classAverageJTextField.setHorizontalAlignment(
         JTextField.CENTER );
      contentPane.add( classAverageJTextField );

      // set properties of application's window
      setTitle( "Class Average" ); // set title bar text
      setSize( 250, 250 );         // set window size
      setVisible( true );          // display window

   } // end method createUserInterface

   // method retrieves, totals and displays grades from user
   private void getGradesJButtonActionPerformed( ActionEvent event )
   {
      total = 0;        // stores total of grades entered
      int counter = 1;  // counter controls do...while statement
      String input;     // stores data entered into input dialog
      int grade;        // stores int value converted from input
      
      // clear previous grades and calculation result
      gradeListJTextArea.setText( "" );
      classAverageJTextField.setText( "" );
      
      do
      {
         // get user input
         input = JOptionPane.showInputDialog( null, "Enter Grade" );
         grade = Integer.parseInt( input );
      
         // add text to output
         gradeListJTextArea.append( grade + "\n" );
         total += grade;                     // add input to total
         counter++;                          // increment counter
      }
      while ( counter <= 10 );               // end do...while
      
      averageJButton.setEnabled( true );     // enable averageJButton
      averageJButton.requestFocusInWindow(); // transfer focus
	  
   } // end method getGradesJButtonActionPerformed
   
   // method calculates average of grades entered
   private void averageJButtonActionPerformed( ActionEvent event )
   {
      double average = ( double ) total / 10;  // calculate average
      classAverageJTextField.setText( String.valueOf( average ) );
      
   } // end method averageJButtonActionPerformed

   // main method
   public static void main( String[] args )
   {
      ClassAverage application = new ClassAverage();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

   } // end method main

} // end class ClassAverage

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