four kinds of design for adding operation of two rationals

有理數加法的幾種設計: 結果回傳或覆蓋 vs 類別或物件方法
  (1) public static Rational add(Ratinoal r1, Rational r2)
      // 用法:  Rational r3 = Rational.add(r1,r2);  // r3=r1+r2

  (2) public static void add(Ratinoal r1, Rational r2)
      // 用法:  Rational.add(r1,r2);  // r1=r1+r2

  (3) public Rational add(Rational r2)
      // 用法:  Rational r3 = r1.add(r2);  // r3=r1+r2

  (4) public void add(Rational r2)
      // 用法:  r1.add(r2);  // r1=r1+r2