有理数类的设计

1.有理数类的代码

package cn.edu.jmu;

public class Rational {
	private int numerator;		//分子
	private int denominator;	//分母
	
	public int getNumerator() {
		return numerator;
	}
	public int getDenominator() {
		return denominator;
	}

	//无参构造函数
	public Rational () {
		this.numerator = 0;
		this.denominator = 1;
	}
	//有参构造函数
	public Rational (int numerator, int denominator) {
		if (numerator < 0 && denominator < 0) {
			this.numerator = -numerator;
			this.denominator = -denominator;
		}else if (numerator > 0 && denominator < 0) {
			this.numerator = -numerator;
			this.denominator = -denominator;
		}else {
			this.numerator = numerator;
			this.denominator = denominator;
		}
	}
	
	//求最大公约数，化简用
	private int gcd(int numerator, int denominator) {
        int x = Math.abs(numerator);
        int y = Math.abs(denominator);
        int tmp;
        while (y != 0) {
            tmp = x % y;
            x = y;
            y = tmp;
        }
        return x;
    }
	
	//相加
	public Rational add (Rational x) {
		int numerator2 = numerator * x.denominator + x.numerator * denominator;
		int denominator2 = denominator * x.denominator;
		return new Rational(numerator2, denominator2);
	}
	//相减
	public Rational subtract (Rational x) {
		int numerator2 = numerator * x.denominator - x.numerator * denominator;
		int denominator2 = denominator * x.denominator;
		return new Rational(numerator2, denominator2);
	}
	//相乘
	public Rational multiply (Rational x) {
		int numerator2 = numerator * x.numerator;
		int denominator2 = denominator * x.denominator;
		return new Rational(numerator2, denominator2);
	}
	//相除
	public Rational divide (Rational x) {
		int numerator2 = numerator * x.denominator;
		int denominator2 = denominator * x.numerator;
		return new Rational(numerator2, denominator2);
	}
	//求绝对值
	public Rational abs () {
		int numerator2 = numerator;
		int denominator2 = denominator;
		if (numerator2 < 0) {
			numerator2 = -numerator2;
		}
		if (denominator2 < 0) {
			denominator2 = -denominator2;
		}
		
		return new Rational(numerator2, denominator2);
	}
	//判断是否相等
	public boolean equals (Rational x) {
		if (this.subtract(x).getNumerator() == 0) {
			return true;
		}else {
			return false;
		}
	}
	//比较大小，大于所比较的数返回1，小于返回-1，等于返回0
	public int compareTo (Rational x) {
		if (this.subtract(x).getNumerator() > 0) {
			return 1;
		}else if (this.subtract(x).getNumerator() < 0) {
			return -1;
		}else {
			return 0;
		}
	}
	//以字符串形式输出
	public String toString () {
		int t = gcd(numerator, denominator);
		numerator /= t;
		denominator /= t;
		
		if(denominator == 1) {
			return numerator+"";
		}else if (numerator == 0) {
			return 0+"";
		}else {
			return numerator + "/" + denominator ;
		}
	}
}

2.测试代码

package demo;

import cn.edu.jmu.Rational;

public class Main {

	public static void main(String[] args) {
		Rational s1 = new Rational(1, 2);
		Rational s2 = new Rational(3, 4);
		Rational s3 = new Rational(8, -7);
		Rational s4 = new Rational(3, 4);
		Rational s5 = new Rational();
		
		System.out.println("s1+s2 = " + s1.add(s2).toString());
		System.out.println("s1-s2 = " + s1.subtract(s2).toString());
		System.out.println("s1*s2 = " + s1.multiply(s2).toString());
		System.out.println("s1/s2 = " + s1.divide(s2).toString());	
		System.out.println("|s3| = " + s3.abs().toString());
		System.out.println("判断s1与s2是否相等：" + s1.equals(s2));
		System.out.println("判断s2与s4是否相等：" + s2.equals(s4));
		System.out.println("s1与s2比大小：" + s1.compareTo(s2));
		System.out.println("无参构造：" + s5.toString());
}

3.运行结果

4.尝试描述怎么与c语言的有理数代码相比较,为什么你设计的类更加面向对象?

c语言是以函数的形式编写，java是以类的形式编写，使用者在使用时只需导入即可，更加的方便，而且定义方法时可以进行重载，可为类似功能的方法提供统一名称，根据参数类型或个数的不同调用相对应的方法。而c语言一个函数只能有一种参数定义。

5.尝试从代码复用的角度来描述你设计的有理数类。从几个方面讨论。

a.别人如何复用你的代码?

导入对应包中的有理数类。例：import cn.edu.jmu.Rational;

b.别人的代码是否依赖你的有理数类的属性?当你的有理数类的属性修改时,是否会影响他人调用你有理数类的代码?

别人的代码依赖我的有理数类的属性。
当我的有理数类的属性修改时，因为属性设置为private，所以不影响他人调用有理数类的代码。

c.有理数类的public方法是否设置合适?为什么有的方法设置为private?

合适。
防止使用者对数据进行错误修改造成程序崩溃；辅助编写public方法的方法，不应被使用者调用。