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/* 
* File:  		ButtonHandler.java 
* Description:  Handle's what happen's when the button is pressed. 
*/ 
 
import java.awt.event.*; 
import java.awt.*; 
 
class ButtonHandler implements ActionListener { 
 
 
private CalcDisplay display;	//holds instance of calculator's display 
private String lastOp;			//holds the last operator that was pressed 
private String strVal;			//holds the string value of the number  
private double total;			//accumulator 
private double number;			//used to store new number's 
 
//flag used to determine if op is pressed for the first time 
private boolean firsttime;		 
 
//flag used to determine if an operator has been pressed 
private boolean operatorPressed;  
 
ButtonHandler( CalcDisplay d ) 
{ 
   display = d;	 
   firsttime = true; 
   strVal = ""; 
} 
 
// this method is called automatically when a button is pressed 
public void actionPerformed( ActionEvent e ) 
{ 
	//store the instance of the button that was pressed 
	ButtonComponent button = (ButtonComponent) e.getSource(); 
	 
	//get the button's label 
	String s = button.getLabel().trim(); 
	 
	//determine if the button was a number or operator button 
	if ( Character.isDigit( s.charAt(0) ) )		 
		handleNumber( s );					 
	else 
	    calculate( s );	    	   		 
} 
 
//determine's whether the operator is unary or binary 
//and does calculation's according to operator type 
void calculate( String op ) 
{ 
  operatorPressed = true; 
	 
  //if it's the firsttime the button has been pressed after: 
  // 
  //		- the program first starts 
  //		- the equal has been pressed 
  //		- or the calculator has been cleared 
  // 
  // set the first number displayed on the display to total 
   
  if ( firsttime && !Operator.isUnary( op ) ){ 
   total = getNumberOnDisplay();  	 
   firsttime = false; 
   }  
     
     
    if ( Operator.isUnary( op ) ) {   	 
    	handleUnaryOp( op );         
    } 
	else if ( lastOp != null ) {		 
		handleBinaryOp( lastOp );		 
	} 
 
   //store the calculator's last op -- important for binary operators 
   if ( !Operator.isUnary( op ) ) 
         lastOp = op; 
            
} 
 
//this method handles unary operators 
void handleUnaryOp( String op ) 
{ 
	 if ( op.equals( Operator.NEGATE ) ) 
       {   
         //negate the number on the display screen 	  
         number = negate( getNumberOnDisplay()+"");    	    	     
         display.append(  number + "" ); 
         return;        	 
       } 
       else if ( op.equals( Operator.DOT ) ) 
       { 
       	 handleDecPoint(); 
       	 return; 
       } 
       else if ( op.equals( Operator.SQRT ) ) 
       {   
         //calculate the square root of the number on the display    	 			      
	     number = Math.sqrt( getNumberOnDisplay() ); 
	     display.append( number+"" ); 
	     return;	     	    
       }       
       else if ( op.equals( Operator.EQUALS ) ) 
       { 
       	 //if a binary operator was pressed before the equals 
       	 //complete the operation first 
       	 if ( lastOp != null && !Operator.isUnary( lastOp ) )  
       	      handleBinaryOp( lastOp ); 
       	  
       	 lastOp = null; 
         firsttime = true; 
         return; 
       } 
       else  
       clear();    
} 
 
// handles operators that require two operands 
void handleBinaryOp( String op ) 
{ 
	if ( op.equals( Operator.ADD ) )  
		 total += number;	 
	else if ( op.equals( Operator.SUBTRACT ) ) 
		 total -= number; 
	else if ( op.equals( Operator.MULTIPLY ) ) 
		 total *= number; 
	else if ( op.equals( Operator.DIVIDE ) ) 
		 total /= number; 
	else if ( op.equals( Operator.POW ) ) 
	     total = Math.pow( total, number ); 
					    
    display.append( total+"" );		    	 
} 
 
//This method is called each time a number is pressed. 
//A string object is used to concatenate each number pressed in succession 
//which then is converted into a double data type. 
 
void handleNumber( String s ) 
{ 
	//concatenate to strVal if an operator was pressed before the current 
	//button 
	if ( !operatorPressed ) 
	strVal+=s; 
	 
	//if an operator was pressed, clear strVal and store the first number 
	//pressed 
	else { 
		operatorPressed = false; 
		strVal = s;		 
	} 
	 
	//convert strVal to double  
	number = new Double( strVal ).doubleValue();	 
	display.append( strVal ); 
	 
} 
 
//this method is called when the decimal point button has been pressed 
void handleDecPoint() 
{ 
	operatorPressed = false; 
	 
	//put a decimal point at the end of strVal only if there is no 
	//decimal point already 
	if ( strVal.indexOf( "." ) < 0 ) { 
	     strVal+=Operator.DOT;	 
	}        
	display.append( strVal ); 
} 
 
//Method used to negate a value 
double negate( String s ) 
{ 
	operatorPressed = false; 
	 
	//if number is a whole number, get rid of the '0' at the end of the 
	//number to allow more number's to be added to the right of the 
	//decimal point. 
	 
	if ( number == ( int ) number ) 
	     s = s.substring( 0, s.indexOf( "." ) ); 
	 
	//add negative sign to the number if it doesn't exist	 
	if ( s.indexOf( "-" ) < 0 ) 
	     strVal = "-"+s; 
	 
	//If a negative sign exist's, remove it 
	else 
	     strVal = s.substring( 1 );	   
	      
return new Double( strVal ).doubleValue();   
} 
 
//get's the number that is currently on the display screen and 
//convert it to double 
double getNumberOnDisplay() { 
   return new Double( display.getText() ).doubleValue();	 
} 
 
//clear's screen and reset's all variables 
void clear() 
{ 
	firsttime = true; 
	lastOp = null; 
	strVal = ""; 
	total = 0; 
	number = 0; 
	display.clear(); 
	display.append( "0" ); 
} 
 
}