How can I get the first 5 numbers of a double-CodePudding

how can i only have the first 5 numbers in a double?

12345.6789 --> 12345
1.23456789 --> 1.2345
0.123456789 --> 0.1234

I have tried different things such as multiplying the number by the power of 10 and x but x seems to only affect the decimal places, setting it to x decimal places

CodePudding user response：

Using BigDecimal:

move the decimal point to the right/left until only the desired number of (significant) digits are in front of the decimal point;
set the scale to zero, that is, removed all digits after the decimal point or extend the precision up to the point (if missing digits);
move the decimal point back to where it was, undoing first step.

static BigDecimal convert(BigDecimal number, int significant) {
    var beforeDecimal = number.precision() - number.scale();
    var movePoint = significant - beforeDecimal;
    return number
           .movePointRight(movePoint)
           .setScale(0, RoundingMode.DOWN)
           .movePointLeft(movePoint);
}

called like
convert(BigDecimal.valueOf(1.23456789), 5)
or
convert(new BigDecimal("1.23456789"), 5)

to return the BigDecimal:
1.2345

CodePudding user response：

Here is one way.

convert to a string.
check for a decimal.
if not present (= -1) or >= 5, set i to 5. Else set to 6
then get the substring from 0 to i.

double[] v = {12345.6789,
1.23456789,
0.123456789};

for (double d : v) {
    String s = Double.toString(d);
    int i = s.indexOf('.');
    i = i < 0 || i >= 5 ? 5 : 6;
    System.out.println(s.substring(0,i));
}

prints

12345
1.2345
0.1234

CodePudding user response：

As others commented, one way to do this is with string manipulation. May not seem elegant, but it gets the job done.

Define some inputs.

double[] doubles = { 12345.6789 , 1.23456789 , 0.123456789 } ;

Loop those inputs. For each one, generate a string. If a FULL STOP is found, take first six characters. If not, five. If the FULL STOP lands in the last place, such as in our first example input, delete.

for( double d : doubles )
{
    String s = String.valueOf( d ) ; 
    String s5 = s.substring( 0 , s.contains( "." ) ? 6 : 5 ) ;
    if( s5.endsWith( "." ) ) { s5 = s5.substring( 0 , s5.length() - 1 ) ; }  // Drop FULL STOP in last place.
    System.out.println( s5 ) ;
}

See this code run live at IdeOne.com.

12345
1.2345
0.1234

Caveat: You may need to internationalize by accounting for a COMMA (,) as the decimal separator rather than a FULL STOP (.) character.

String s5 = s.substring( 0 , ( s.contains( "." ) || s.contains( "," ) ) ? 6 : 5 ) ;