例如一個數字 -123456.1234 轉換成 -1.2346*10^5

public class FormatNumber {
	
	public static String format(double num){
		String neg = "";
		if(num<0){
			num *= -1;
			neg = "-";
		}
		int n = (int)Math.log10(num);
		
		num = num / Math.pow(10, n);
		num *= Math.pow(10, 4);
		num = Math.round(num);
		num /= Math.pow(10, 4);
		return neg+num+"*10^"+n;
	}
	
	public static void main(String [] args){
		int n = (int) Math.log10(0.00100);
		System.out.println(format(-12345.689));
	}

}