calculator.java

计算器的源代码,比较简单!

// Calculator.java
//<applet code = Calculator.class,width = 200,height = 50></applet>
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class Calculator extends JApplet implements ActionListener , KeyListener
{
	boolean flag = false, first = true;
	int opTag = 0, numTag = 0;
	int[] op = new int[ 2 ];
	double[] num = new double[ 2 ];
	public String[] s = {"7", "8", "9", "+", "4", "5", "6", "-", "1", "2", "3", "*", "0", ".", "=", "/", "Back", "CE", "C"};

	JTextField textfield = new JTextField( 10 );
	JPanel p4 = new JPanel();	

  	public void init()
  	{
    	Container container = getContentPane();
    	container.setLayout( new BorderLayout( 10, 10) );

    	// Create panel p1 for the buttons and set GridLayout
    	textfield.setHorizontalAlignment( JTextField.RIGHT );
    	textfield.setText( "0.0" );

    	p4.setLayout( new BorderLayout());
		p4.add( textfield, BorderLayout.CENTER);
    	    	
    	JPanel p1 = new JPanel();
    	p1.setLayout( new GridLayout( 4, 3, 5, 5 ) );
    	JPanel p2 = new JPanel();
    	p2.setLayout(new GridLayout( 1, 3, 10, 20 ) );
    	
    	// Add buttons to the panel
    	for( int i = 0; i < 19; i ++ )
    	{
    		JButton button = new JButton();
    		button.setText( s[i] );
    		button.addKeyListener( this );
    		button.addActionListener( this );
    		if( i < 16 )
    			p1.add( button );
    		else
    			p2.add( button );
    	}
    
    	//Add p2 and a textfield to the panel
     	JPanel p3 = new JPanel();
     	p3.setLayout( new BorderLayout( 10, 10) );
    	p3.add( p4, BorderLayout.NORTH );
    	p3.add( p2, BorderLayout.CENTER );  

    	//Add p3 and p1 to the containter
    	container.add( p3, BorderLayout.NORTH );
    	container.add( p1, BorderLayout.CENTER ); 
		p4.addKeyListener( this ); 
   	}
   	
   	public void focus()
	{
		p4.requestFocus();
	}

  	// Main method
  	public static void main( String[] args )
  	{
    	Calculator applet = new Calculator();
    	JFrame frame = new JFrame();
    	frame.setTitle( "Calculator" );
    	frame.getContentPane().add(applet, BorderLayout.CENTER);
    	
    	applet.init();
    	applet.start();
	   	frame.pack();
    	frame.setVisible( true );
    	frame.setLocation( 350, 250 );
    	applet.focus();
  	}
  	
  	public void actionPerformed( ActionEvent e ) 
	{  	 
  		String actionCommand = e.getActionCommand();		 
  		if ( e.getSource() instanceof JButton )
			input( actionCommand );
	}
	
	public void keyReleased(KeyEvent e)
  	{
  	}

  	public void keyTyped(KeyEvent e)
  	{
  	}

  	public void keyPressed(KeyEvent e)
  	{
  		String actionCommand =  String.valueOf( e.getKeyChar() );
  		
  		/** deal the exception -- the input is not a number */
		try
		{
			int j = 0;
			for( int i = 0; i < 16; i ++ )
				if( actionCommand.equals( s[ i ] ) || e.getKeyChar() == '\b' || e.getKeyChar() == '\n' )
					j ++;
			if( j == 0 )
				throw new NotNumberException( actionCommand );
		}
		catch( NotNumberException ex )
  		{
  			textfield.setText( "0.0" );
  			System.out.println( ex );
  		}
  		
  		input( actionCommand );
  	}
	
	/** input the arithmetic and get its result */
	public void input( String actionCommand )
	{
		for( int i = 0; i < 10; i ++ )
   			if ( Integer.toString( i ).equals( actionCommand ) )
   			{
      	 		if( flag == false )
      	 		{
      	 			textfield.setText( String.valueOf( i ) );
      	 			flag = true;
      	 		}
      	 		else
      	 			textfield.setText( textfield.getText().trim() + i );
      	 		num[ numTag ] = Double.parseDouble( textfield.getText().trim() );
      	 		if( numTag == 1)
      	 			first = false;
      	 	}
      			
      	if( ".".equals( actionCommand ) )
      		textfield.setText( textfield.getText().trim() + "." );
      		
      	if( flag == true && ( "Back".equals( actionCommand ) || String.valueOf( '\b' ).equals( actionCommand ) ) )
      		if( Integer.parseInt( textfield.getText().trim() + 1 ) != 1 )
      			textfield.setText( textfield.getText().substring( 0, textfield.getText().trim().length() - 1 ) );
      	
      	if( "CE".equals( actionCommand ) )
      	{
      		textfield.setText( "0.0" );
     		flag = false;
      	}
      	
      	if( "C".equals( actionCommand ) )
      	{
      		textfield.setText( "0.0" );
      		for( int i = 0; i < 2; i ++ )
      			num[ i ] = 0;
      		op[ 0 ] = 1;
      		numTag = 0;
      		flag = false;
      		first = true;
      	}
      			
      	/** deal the exception -- Denominator is zero */
      	try
      	{
      		if( "+".equals( actionCommand ) )
       			opOperate( 1 );
      			
      		if( "-".equals( actionCommand ) )
      			opOperate( 2 );
      			
	      	if( "*".equals( actionCommand ) )
    	  		opOperate( 3 );
		 
      		if( "/".equals( actionCommand ) )
      			opOperate( 4 );
      	
	      	if( "=".equals( actionCommand ) || String.valueOf( '\n' ).equals( actionCommand ) )
    	  	{
      			if( flag == false && numTag == 1 )
					num[ 1 ] = num [ 0 ];
	      		num[ 0 ] = operate( num[ 0 ], num[ 1 ], op[ 0 ] );
    	  		textfield.setText( Double.toString( num[ 0 ] ) );
      			first = true;
      			numTag = 0;
	      		flag = false;
    	  	}
    	}
    	catch( Exception ex )
    	{
    		textfield.setText( "0.0" );
    		System.out.println( ex );
    	}
    }
    
    /** the method of calculation and display */
    public void opOperate( int n ) 
    {
    	if( first == true )
    		opTag = 0;
    	else
    		opTag = 1;
    	op[ opTag ] = n;
    	
    	if( first == false )
 		{
 			num[ 0 ] = operate( num[ 0 ], num[ 1 ], op[ 0 ] );
 			op[ 0 ] = op[ 1 ];
 			textfield.setText( String.valueOf( num[ 0 ] ) );
 		}
    	flag = false;
 		numTag = 1;      		
 	}
 		
	/** the method of calculator */
	public double operate( double x, double y, int op ) throws RuntimeException
	{
		switch( op )
		{
			case 1 : 
				return x + y;
			case 2 : 
				return x - y;
			case 3 : 
				return x * y;
			case 4 : 
				if( y == 0 )
					throw new RuntimeException( "Denominator cannot be zero" );
				else 
					return x / y;		
		}
		return 0;
	}
	
	/** the notnumberexception */
	private class NotNumberException extends Exception
	{
		private String letter;
  
  		public NotNumberException( String letter )
 		{
    		super( "It can't be a letter!" );
   		 	this.letter = letter;
  		}
  		
  		public String getLetter()
  		{
  			return letter;
  		}
	}
}