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Converting Numbers to Strings

Sometimes, you need to convert a number to a string because you need to operate on the value in its string form. All classes inherit a method called toString from the Object class. The type-wrapper classes override this method to provide a reasonable string representation of the value held by the number object. The following program, ToStringDemo, uses the toString method to convert a number to a string. Next, the program uses some string methods to compute the number of digits before and after the decimal point:

public class ToStringDemo {
    public static void main(String[] args) {
        double d = 858.48;
        String s = Double.toString(d);

        int dot = s.indexOf('.');
        System.out.println(s.substring(0, dot).length()
                           + " digits before decimal point.");
        System.out.println(s.substring(dot+1).length()
                           + " digits after decimal point.");
    }
}

The output of this program is:

3 digits before decimal point.
2 digits after decimal point.

The toString method called by this program is the class method. Each of the number classes has an instance method called toString, which you call on an instance of that type.

You don't have to explicitly call the toString method to display numbers with the System.out.println method or when concatenating numeric values to a string. The Java platform handles the conversion by calling toString implicitly.

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