温度转换在JFrame中无法正常工作

Question

I can not seem to figure out what I am doing wrong in my Event Handler; and I am not a good programmer. I can convert from Celsius to Fahrenheit but not the other way around. It usually shows 0.0 for Fahrenheit to Celsius conversions. I think it might have something to do with cfList which is my JComboBox to choose Celsius or Fahrenheit.

Also I want to be able to click the convert button without putting in a value, and the JTextField will automatically be set to zero and show a message that says "Value set to zero."

So how can I get this whole thing to work:

• Convert Celsius to Fahrenheit
• Convert Fahrenheit to Celsius
• Convert Celsius to Fahrenheit without a value(set to zero)

• Convert Fahrenheit to Celsius without a value(set to zero)

   class TCalcButtonHandler implements ActionListener { public void actionPerformed(ActionEvent e) { double far, cel; String ff, cc; String inString; inString = tempField.getText(); if(inString==null && cfList.getSelectedIndex() == 0) { degree.setText("F"); cel=0; far = cel*(9/5)+32; ff = far+""; resultField.setText(ff); tempSysField.setText("Value set to zero"); } if(inString==null && cfList.getSelectedIndex() == 1) { degree.setText("C"); far=0; cel = (5/9)*(far-32); cc = cel+""; resultField.setText(cc); tempSysField.setText("Value set to zero"); } if(cfList.getSelectedIndex()==0 && inString!=null) { degree.setText("F"); cel = Double.parseDouble(inString); far = cel*(9/5)+32; ff = far+""; resultField.setText(ff); tempSysField.setText(""); } if(cfList.getSelectedIndex()==1 && inString!=null) { degree.setText("C"); far = Double.parseDouble(inString); cel = (far-32)*(5/9); cc = cel+""; resultField.setText(cc); tempSysField.setText(""); } } } 

Answer 1

Your question title states:

Temperature Conversion not working properly ...

Almost always this is due to your doing int division unknowingly, and in fact, that's exactly what is going on:

far = cel*(9/5)+32;

Change 9/5 to 9.0/5.0

far = cel * (9.0 / 5.0) + 32;

Why is this important? int division (dividing one int by another) always returns an int, with the fractional part truncated away. So 9/5 returns 1 and 5/9 returns 0. If you want the calculation to retain the fractional portion, then at least one double has to be part of the division equation, so in fact 9.0 / 5 would work just fine as would ((double)9/5)