Programming and Problem Solving with Java

CASE STUDY

418

staticJButton subtract; // Subtract button

staticJButton clear; // Clear button

// Define event listener for numeric buttons

static classNumericHandler implements ActionListener

{

public voidactionPerformed(ActionEvent event)

// Handle events from the buttons in calcPane

{

double secondOperand; // Holds input value

String whichButton; // Holds the button's name

// Get the operand

secondOperand =

Double.parseDouble(inputField.getText());

whichButton = event.getActionCommand(); // Get the button's name

if(whichButton.equals("+")) // When the name is "add"

result = result + secondOperand; // add the operand

else // Otherwise

result = result – secondOperand; // subtract the operand

register.setText(""+ result); // Display result

inputField.setText(""); // Clear input

}

}

static class ClearHandler implementsActionListener

{

public voidactionPerformed(ActionEvent event)

// Handle events from the Clear button in calcPane

{

result = 0.0; // Set result back to zero

register.setText("0.0"); // Reset result in register

inputField.setText(""); // Clear input

}

}

public static voidmain(String[] args)

{

operation = newNumericHandler(); // Instantiate a NumericHandler

clearOperation = newClearHandler(); // Instantiate a ClearHandler

result = 0.0; // Initialize result

// Instantiate labels and initialize input field

resultLabel = newJLabel("Result:");

register = newJLabel("0.0", JLabel.RIGHT);

entryLabel = newJLabel("Enter #:");

inputField = newJTextField("", 10 );