Code:
// Calc7 - A four-function calculator with error checking
import
java.awt.*;
import
java.applet.*;
public class Addingmachine extends Applet
{
// ---------------------------------------------------------
// Attributes:
// TextArea total displays running total of calculations
// Label output shows current number being entered
// doubles memVal and curVal are used for calculations
// ---------------------------------------------------------
TextArea
total = new TextArea("", 5, 25, TextArea.SCROLLBARS_VERTICAL_ONLY);
Label
output = new Label();
double memVal = 0;
double curVal = 0;
// ---------------------------------------------------------
// The init() method sets the layout and color.
// It then calls the makeButtons() to do the actual layout
// for the calculator
// ---------------------------------------------------------
public void init()
{
setLayout(
new BorderLayout(5, 5));
setBackground(Color.
lightGray);
add(
"Center", makeButtons());
}
// ---------------------------------------------------------
// The action() method handles the button presses. Since
// this is a Java 1.0 applet, all button actions go through
// the action() method.
// ---------------------------------------------------------
public boolean action(Event ev, Object o)
{
// Local variables
String arg = (String) o;
// Key that was pressed
char c = arg.charAt(0); // First char of key caption
String s =
output.getText(); // Current value of output
// "Special" keys operate on current value
if (arg.equals("Backspace"))
backSpace(s);
else if (arg.equals("C"))
clearAll();
else if (arg.equals("CE"))
clearEntry();
else if (arg.equals("sqrt"))
setCurVal(Math.sqrt(
curVal));
else if (arg.equals("1/x"))
setCurVal(1.0 /
curVal);
else if (arg.equals("+/-"))
setCurVal(-
curVal);
// Digit keys are always added to current value
else if (c >= '0' && c <= '9')
setCurVal(s + c);
// Decimal point added only if not already in output
else if (c == '.')
{
if (s.indexOf(c) < 0)
setCurVal(s + c);
}
// Handle all of the operator keys
else
{
switch (c)
{
case '/':
memVal /= curVal;
break;
case '*':
memVal *= curVal;
break;
case '-':
memVal -= curVal;
break;
case '+':
memVal += curVal;
break;
case '%':
memVal %= curVal;
break;
case '=':
memVal = curVal;
total.append(padText("=============\n", 25));
break;
}
// Display results on the TextArea named total
String memstr =
"" + curVal + " " + c + " \n";
total.append(padText(memstr, 25));
memstr =
"" + memVal + " \n";
total.append(padText(memstr, 25));
// Clear the output Label
curVal = 0;
output.setText("");
}
return true;
}
// ----------------------------------------------------------
// These are utility methods
// ----------------------------------------------------------
String padText(String s,
int size)
{
String temp =
" " + s;
return temp.substring(temp.length() - size);
}
// Handles the backspace key
void backSpace(String s)
{
if (output.getText() != null && !output.getText().equals("")) {
s = s.substring(0, s.length() - 1);
setCurVal(s);
}
else {
}
}
// Handles the 'C' [Clear All] key
void clearAll()
{
total.setText("");
output.setText("");
curVal = memVal = 0;
}
// Handles the 'CE' [Clear Entry] key
void clearEntry()
{
output.setText("");
curVal = 0;
}
// Sets the current value, using a String
void setCurVal(String s)
{
output.setText(s);
curVal = (new Double(s)).doubleValue();
}
// Sets the current value, using a number
void setCurVal(double newValue)
{
curVal = newValue;
String dstring = Double.toString(newValue);
output.setText(dstring);
}
// ---------------------------------------------------------
// This lays out the appearance of the applet, using
// BorderLayout and GridLayout
// The colors used for the buttons may, or may not, appear
// on your copy, depending upon your Web browser
// ---------------------------------------------------------
Panel makeButtons()
{
// Create 4 Panels [p1 through p4]
Panel p =
new Panel(new BorderLayout(5, 5));
Panel p1 =
new Panel(new BorderLayout(5, 5));
Panel p2 =
new Panel(new BorderLayout(5, 5));
Panel p3 =
new Panel(new GridLayout(1, 3, 5, 5));
Panel p4 =
new Panel(new GridLayout(4, 5, 5, 5));
Panel p5 =
new Panel(new BorderLayout(5, 5));
// Add Backspace, CE, and C buttons to p3
p3.setForeground(
new Color(232, 0, 0));
p3.setFont(
new Font("Dialog", Font.PLAIN, 12));
p3.add(
new Button("Backspace"));
p3.add(
new Button("CE"));
p3.add(
new Button("C"));
// Add Number buttons to p4
p4.setForeground(
new Color(0, 0, 235));
p4.setFont(
new Font("Dialog", Font.PLAIN, 14));
p4.add(
new Button("7"));
p4.add(
new Button("8"));
p4.add(
new Button("9"));
p4.add(
new Button("/"));
p4.add(
new Button("sqrt"));
p4.add(
new Button("4"));
p4.add(
new Button("5"));
p4.add(
new Button("6"));
p4.add(
new Button("*"));
p4.add(
new Button("%"));
p4.add(
new Button("1"));
p4.add(
new Button("2"));
p4.add(
new Button("3"));
p4.add(
new Button("-"));
p4.add(
new Button("1/x"));
p4.add(
new Button("0"));
p4.add(
new Button("+/-"));
p4.add(
new Button("."));
p4.add(
new Button("+"));
p4.add(
new Button("="));
// Add and initialize output and total
// [Label and TextArea for output]
// output.setBackground(Color.WHITE);
// output.setForeground(Color.BLACK);
// output.setFont(new Font("Courier", Font.BOLD, 18));
total.setBackground(new Color(255, 255, 128));
total.setForeground(Color.black);
total.setFont(new Font("Courier", Font.BOLD, 14));
p5.add(
"Center", total);
p5.add(
"South", output);
// Hook up the panels
p2.add(
"North", p3);
p2.add(
"Center", p4);
// Add some spacing around outside
p1.add(
"North", p5);
p1.add(
"Center", p2);
p.setFont(
new Font("Helvetica", Font.PLAIN, 6));
p.add(
"North", new Label(" "));
p.add(
"East", new Label(" "));
p.add(
"West", new Label(" "));
p.add(
"South", new Label(" "));
p.add(
"Center", p1);
return p;
}
}
It's a calculator that works like an old adding machine. But it keeps throwing an error when trying to use operands. I'm supposed to write a try-catch to catch the error and deal with it. I can't find out where the error is, or how to catch it. Thanks for any help.
12-13-08
Java try-catch help
