[問題] 繼承與多型的新手問題(已修改問題)

看板java作者wtchen (沒有存在感的人)時間11年前 (2014/01/22 18:18)推噓6(6推 0噓 6→)

留言12則, 3人參與討論串1/1

最近在自學data structure的分數運算(真的是自學，非作業) 我c++已有很久經驗，可是到了java(剛開始碰)很多轉不過來， (應版主要求把程式貼全，並重新發問) class Rational { protected long numerator; protected long denominator; public Rational() { // assume the rational number is 0 numerator = 0; denominator = 1; } public Rational(long i) { numerator = i; denominator = 1; } public Rational(long num,long denom) { numerator = num; denominator = denom; } public void setRational(long i,long j) { numerator = i; denominator = j; } public void print() { System.out.println("Rational is :" + numerator + "/" + denominator); } public void error(String message) { System.out.println(message); } public void reduce() { long a, b, rem, sign; sign = 1; if ( numerator == 0 ) { denominator = 1; }else if ( numerator == denominator ) { denominator = 1; numerator = 1; }else if ( numerator < 0 && denominator < 0 ) { numerator = -numerator; denominator = -denominator; }else if ( numerator < 0 ) { numerator = -numerator; sign = -1; }else if ( denominator < 0) { denominator = -denominator; sign = -1; } if (numerator>denominator) { a = numerator; b = denominator; }else { a = denominator; b = numerator; } while (b != 0) { rem = a%b ; a = b ; b = rem ; } numerator = sign * numerator / a ; denominator = denominator / a ; } public Rational add(Rational r) { long k, denom, num; Rational rnl = new Rational() ; reduce(); r.reduce(); rnl.setRational(denominator, r.denominator); rnl.reduce(); k = rnl.denominator; denom = denominator * k; num = numerator * k + r.numerator*denom/k; rnl.setRational(num, denom); rnl.reduce(); return rnl; } public Rational add(long i) { Rational r = new Rational() ; r.setRational(i,1); return add(r); } public Rational sub(Rational r) { long k, denom, num; Rational rnl = new Rational() ; reduce(); r.reduce(); rnl.setRational(denominator, r.denominator); rnl.reduce(); k = rnl.denominator; denom = denominator * k; num = numerator * k - r.numerator*denom/k; rnl.setRational(num, denom); rnl.reduce(); return rnl; } public Rational mult(Rational r) { reduce(); r.reduce(); Rational rnl1 = new Rational(numerator, r.denominator); Rational rnl2 = new Rational(r.numerator, denominator); Rational rnl3 = new Rational(); rnl1.reduce(); rnl2.reduce(); rnl3.setRational(rnl1.numerator*rnl2.numerator, rnl1.denominator*rnl2.denominator); return rnl3; } public Rational divide(Rational r) { reduce(); r.reduce(); Rational rnl = new Rational(r.denominator, r.numerator); return mult(rnl); } public int equal(Rational r) { reduce(); r.reduce(); if (numerator == r.numerator && denominator == r.denominator) { return 1; }else { return 0; } } } class Rational2 extends Rational //這邊是想用Rational2繼承Rational後增加一個setRational { public void setRational(long num) { numerator = num; denominator = 1; } public Rational2() //純粹繼承 { super(); } public Rational2(long i) { super(i); } public Rational2(long num,long denom) { super(num, denom); } public Rational2 divide(Rational2 r) //這邊會出問題，不寫一樣不能編譯 { super(r); } } public class Integer { public static void main(String []args) { Rational2 a = new Rational2() ; a.setRational(18,69); Rational2 b = new Rational2(22,8); // Rational2 c = a.divide(b) ; b.print( ); System.out.println(a.equal(b)); System.out.println(System.getProperty("os.arch")); // c.error("test"); } } 編譯錯誤訊息： Integer.java:211: error: incompatible types Rational2 c = a.divide(b) ; ^ required: Rational2 found: Rational 1 error 請問這種情況下要怎麼改才對？我只是在練習c++/java之間的對換，謝謝當 Rational2 繼承 Rational以後原來的Rational divide(Rational)要怎麼讓Rational2也能使用？ (就是Rational2 divide(Rational2) 跟 Rational2 divide(Rational)都能用？) -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 86.200.55.194