adding 2 BigDecimal values [duplicate]

Question

class Point {    BigDecimal x;   BigDecimal y;    Point(double px, double py) {     x = new BigDecimal(px);     y = new BigDecimal(py);   }    void addFiveToCoordinate(String what) {     if (what.equals("x")) {       BigDecimal z = new BigDecimal(5);       x.add(z);     }   }    void show() {     System.out.print("\nx: " + getX() + "\ny: " + getY());   }    public BigDecimal getX() {     return x;   }    public BigDecimal getY() {     return y;   }    public static void main(String[] args) {     Point p = new Point(1.0, 1.0);     p.addFiveToCoordinate("x");     p.show();   } } 

Ok, I would like to add 2 BigDecimal values. I'm using constructor with doubles(cause I think that it's possible - there is a option in documentation). If I use it in main class, I get this:

x: 1 y: 1 

When I use System.out.print to show my z variable i get this:

z: 5 

Answer 1

BigDecimal is immutable. Every operation returns a new instance containing the result of the operation:

 BigDecimal sum = x.add(y); 

If you want x to change, you thus have to do

x = x.add(y); 

Reading the javadoc really helps understanding how a class and its methods work.