一个简单的java程序

public class datatest {double x,y,z;datatest(double xx, double yy, double zz){x = xx;y = yy;z = zz;}private void setX(double xx){x = xx;}private void setY(double yy){y = yy;}private void setZ(double zz){z = zz;}private double distance(){return (x*x+y*y+z*z);}public static void main(String[] args) {datatest test = new datatest(1, -2, 3);System.out.println(test.distance());test.setX(0);System.out.println(test.distance());test.setY(0);System.out.println(test.distance());test.setZ(0);System.out.println(test.distance());}}