Question

I am now working on an android calculator and have some problems on displaying the result…the display is now set using string.format rounding at 9 decimal places…but though this is true for displaying endless decimal results, many other situations are not necessary, like

1+2 should display 3 instead of 3.000000000;

2.03*3 should display 6.09 instead of 6.090000000

1. how could i do this? ask the program to see whether the last digit is 0 and if yes, to replace by “”?
2. how could i display “,’ for each thousand place? ie. 123,456,789 instead of solely 123456789 for both input and answer?

NEW PROBLEM ARISED!!

I newly discovered that after incorporating with the suggestions, for small figures manipulations like under 1000, the displayed answer is ok ( eg 999 * 999 probably displaying 998001). Yet If figures are over, the displayed answer become like this way, eg 9999 * 9999 = 9.998001e7. Is it related to the limitation of double? if then, how could it be solved?

the original coding is as follows:

    case MULTIPLY:                
        inputnum1 = inputnum.get(0); 
        inputnum2 = inputnum.get(1); 

        inputnum.removeAll(inputnum); 

        inputnum.add(inputnum1 * inputnum2); 

        Display.setText(String.format("%.9f", inputnum.get(0)));  
//
            String str1=Display.getText().toString();
            String stripped1 = Double.valueOf(str1).toString(); 
            Display.setText(stripped1);
//              
            break;

the updated code as follows:

    private void calculation (int operator) { 

        inputnum.add(Double.parseDouble(Display.getText().toString())); 

        if (operator != EQUALS) {nextOperation = operator;}
        else if (operator == EQUALS){nextOperation = 0;} 

        switch (currentOperation) { 
    case MULTIPLY: 
        inputnum1 = inputnum.get(0); 
        inputnum2 = inputnum.get(1); 

        inputnum.removeAll(inputnum); 

        inputnum.add(inputnum1 * inputnum2); 

        Display.setText(String.format("%.19f", inputnum.get(0)));  

        DecimalFormat myFormatter3 = new DecimalFormat("###,###,###,###,###,###.#########"); 
        String str3=Display.getText().toString(); 
        String stripped3 = Double.valueOf(str3).toString(); 
        stripped3 = myFormatter3.format(Double.valueOf(stripped3)); 
        if (stripped3.endsWith(".0")) 
            stripped3 = stripped3.substring(0, stripped3.length() - 2); 
        Display.setText(stripped3);

similar for
case SUBTRACT:
case ADD:
case DIVISION:

Many thanks!

Answer 1

The commas are easy to add:

public class DecimalFormatDemo {

static public void customFormat(String pattern, double value ) {
  DecimalFormat myFormatter = new DecimalFormat(pattern);
  String output = myFormatter.format(value);
  System.out.println(value + "  " + pattern + "  " + output);
}

static public void main(String[] args) {

  customFormat("###,###.###", 123456.789);
  customFormat("###.##", 123456.789);
  customFormat("000000.000", 123.78);
  customFormat("$###,###.###", 12345.67);  
}
}

The zeros go like this, I believe:

DecimalFormat myFormatter = new DecimalFormat("###,###,###,###.###");
String str1=Display.getText().toString();
String stripped1 = Double.valueOf(str1).toString();
stripped1 = myFormatter.format(Double.valueOf(stripped1));
if (stripped1.endsWith(".0"))
    stripped1 = stripped1.substring(0, stripped1.length() - 2);
Display.setText(stripped1);