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Jose Caban
207
CS1322/p6/Extra Credit/EventHandler.java
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207
CS1322/p6/Extra Credit/EventHandler.java
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/**
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* <PRE>
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* EventHandler.java
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*
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* Revisions: 1.1 Mar. 14, 2001
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* Added minor modifications to event handling behavior. Added
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* some documentation.
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* 1.0 Jan. 13, 2001
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* Created the EventHandler class
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*
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* </PRE>
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*
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* @author <A HREF="mailto:demox@cc.gatech.edu">Luke A. Olbrish</A>
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* @version Version 1.0, Jan. 13, 2001
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*/
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import java.awt.event.*;
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public class EventHandler implements ActionListener
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{
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// Data Block
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/**
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* The actual gui that will be the view for this program.
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*/
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private CalculatorGUI gui = null;
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/**
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* This is the model that will actually perform calculations.
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*/
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private Calculator calc = null;
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/**
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* This state variable will be used to keep track of whether the number
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* on the display needs to be replaced by new digits.
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*/
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private boolean isNumberStarted = false;
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// Constructors
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/**
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* Creates a new event handler that is bound by the gui view thats passed
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* as a parameter.
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*
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* @param gui the view that this control connects to.
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*/
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public EventHandler( CalculatorGUI gui )
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{
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// If the gui is null, then this class is being used improperly and should
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// exit.
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if( gui == null )
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System.exit( 0 );
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// Add the model and view to the control.
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this.gui = gui;
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this.calc = new Calculator();
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}// end of constructor( CalculatorGUI )
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// Action Listener
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/**
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* This function recieves an action event and interprets the event to take
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* the proper action. It receives all the button actions from
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* CalculatorGUI.
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*
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* @param ae the action event that needs to be processed.
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*/
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public void actionPerformed( ActionEvent ae )
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{
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// No action to process.
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if(( ae == null ) ||
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( ae.getActionCommand() == null ))
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return;
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// Clear the calculator screen and model.
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if( ae.getActionCommand().equals( "Clr" ) )
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doClearCalculator();
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// Find out if an operation was selected and handle it.
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switch( ae.getActionCommand().charAt(0) )
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{
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case '=':
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doCalculation();
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break;
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case '+':
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doSetOp( Calculator.ADD_OP );
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break;
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case '-':
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doSetOp( Calculator.SUB_OP );
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break;
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case '*':
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doSetOp( Calculator.MUL_OP );
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break;
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case '/':
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doSetOp( Calculator.DIV_OP );
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break;
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default:
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break;
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}// end of switch
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// Find out if a digit was pressed
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if( Character.isDigit( ae.getActionCommand().charAt(0) ) )
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doAddDigit( ae.getActionCommand() );
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}// end of actionPerformed( ActionEvent )
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// Operational Functions
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/**
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* This function assists the EventHandler by doing the actions needed to
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* add a digit to the display.
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*
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* @see #actionPerformed
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* @param digit a string that should have a single digit contents.
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*/
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private void doAddDigit( String digit )
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{
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// If diplay needs to be cleared before the digit is added.
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if( !isNumberStarted )
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{
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gui.setDisplay( digit );
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isNumberStarted = true;
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}
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else
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gui.setDisplay( gui.getDisplay() + digit );
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}// end of doAddDigit( String )
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/**
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* Clears the gui display and resets the calculator model.
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*
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* @see #actionPerformed
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*/
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private void doClearCalculator()
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{
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isNumberStarted = false;
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gui.setDisplay( " " );
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calc.clearCalulator();
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return;
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}// end of doClearCalculator()
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/**
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* Attempts to do a calculation. GUI is updated based on whether a
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* calculation occurs and returns the calculation to the gui.
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*
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* @see #actionPerformed
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*/
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public void doCalculation()
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{
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// holds the parsed operator #2.
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int val = 0;
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try
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{
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// Attempt to parse an int from the gui.
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val = Integer.parseInt( gui.getDisplay() );
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// If preconditions are met, then attempt a calculation.
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if(( calc.isOperator1Set() ) &&
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( calc.isOperationSet() ))
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{
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// Calculate and update gui.
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calc.setOperator2( val );
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gui.setDisplay( "" + calc.getCalculation() );
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// Reset display to take in numbers.
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isNumberStarted = false;
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}// end of if
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}// end of try
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catch( NumberFormatException nfe )
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{
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calc.clearCalulator();
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gui.setDisplay( "Error!" );
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return;
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}// end of catch( NumberFormatException )
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catch( ArithmeticException ae )
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{
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calc.clearCalulator();
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gui.setDisplay( "Calc. Error!" );
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return;
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}// end of catch( ArithmeticException )
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}// end of doCalculation()
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/**
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* Set the operation for the calculation. If the operation is already set,
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* then do a calculation then set the operation.
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*
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* @see #actionPerformed
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*/
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public void doSetOp( int operation )
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{
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try
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{
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// Do calculation if operation is already set.
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if( calc.isOperationSet() )
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doCalculation();
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// Set the first operator and set the operation.
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calc.setOperator1( Integer.parseInt( gui.getDisplay() ));
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calc.setOperation( operation );
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isNumberStarted = false;
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}// end of try.
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catch( NumberFormatException nfe )
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{
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calc.clearCalulator();
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gui.setDisplay( "Error!" );
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}// catch( NumberFormatException )
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}// end of doSetOp( int )
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}// end of class EventHandler
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