DecimalFormat df = new DecimalFormat("#.##");
Double number_total = Double.parseDouble(df.format(total));

ERROR:
java.lang.IllegalArgumentException: Bad class: class java.lang.String
    at java.text.NumberFormat.format(NumberFormat.java:304)
    at java.text.DecimalFormat.format(DecimalFormat.java:702)
    at java.text.Format.format(Format.java:93)
    at
com.example.jc.salesman.MainActivity.Totais(MainActivity.java:338)
    at
com.example.jc.salesman.MainActivity$2.onClick(MainActivity.java:235)


String strSum = ((String.format("%.2f", Double.toString(sum))));

ERROR:
Process: com.example.jc.salesman, PID: 26845
java.util.IllegalFormatConversionException: %f can't format
 java.lang.String arguments
    at java.util.Formatter.badArgumentType(Formatter.java:1489)
    at java.util.Formatter.transformFromFloat(Formatter.java:2038)
    at java.util.Formatter.transform(Formatter.java:1465)
    at java.util.Formatter.doFormat(Formatter.java:1081)
    at java.util.Formatter.format(Formatter.java:1042)
    at java.util.Formatter.format(Formatter.java:1011)
    at java.lang.String.format(String.java:1999)
    at java.lang.String.format(String.java:1973)
    at


   com.example.jc.salesman.MainActivity.Totais(MainActivity.java:368)

public void Total (String total){

        Log.d("log2","total: " + total);// it prints 30.00

Double number_total = Double.parseDouble(total);

        Log.d("log2","number_total: " + total);// it prints 30.0
 losing a decimal place.

array_Total.add (number_total); //Arraylist<Double
sum (double) = sum + number_total;
    String strSum = (Double.toString(sum));
total.setText (strSum)
}