Java及Javascript中的浮点运算

package number;

import java.math.BigDecimal;

public class NumberTest {
 
  public static void main(String[] args){
 
    double a =  2.05d;
    BigDecimal c = new BigDecimal(a);
    System.out.println("using double--");
    System.out.println("a * 100 = " + a + " * 100 = " + a*100);
    System.out.println("using BigDecimal--");
    BigDecimal m = new BigDecimal("2.05").multiply(new BigDecimal(100)); //<-- please use this.
    System.out.println("a * 100 = " + a + " * 100 = " + m);
    
    BigDecimal n = new BigDecimal(2.05d).multiply(new BigDecimal(100));
    System.out.println("a * 100 = " + a + " * 100 = " + n);

  }

}

using double--
a * 100 = 2.05 * 100 = 204.99999999999997
using BigDecimal--
a * 100 = 2.05 * 100 = 205.00  
a * 100 = 2.05 * 100 = 204.99999999999998223643160599749535322189331054687500

var c=3.4-3;

alert(c);

alert(parseFloat(c).toPrecision(12)));