如何在分数计算器中获得混合分数，负分数和减少的分数？

Question

我正在尝试用Java创建一个分数计算器，它包含整数，混合分数，不正确分数和负分数。我现在唯一可以使用的是乘法，加法，减法和除以简单分数。我需要能够减少它们。到目前为止，这是我的代码。

import java.util.Scanner;
import java.lang.*;
public class Project2 {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner input = new Scanner(System.in);
    System.out.println("Enter an expression or quit"); //asks user
    String num1 = input.next();
    String operation = input.next();
    String num2 = input.next();

    String nume1 = num1.substring(0,1); //first numerator
    int newNume1 = Integer.parseInt(nume1);  //convert to int
    String deno1 = num1.substring(2,3);  //first denominator
    int newDeno1 = Integer.parseInt(deno1);  //convert to int

    String nume2 = num2.substring(0,1);  //second numerator
    int newNume2 = Integer.parseInt(nume2);  //convert to int
    String deno2 = num2.substring(2,3);  //second denominator
    int newDeno2 = Integer.parseInt(deno2);  //convert to int


    if(num1.equals("quit")){
        System.out.println("Goodbye!");
    }
    else{
        //prints fraction
        System.out.println("Fraction 1: " + num1);
        System.out.println("Operation: " + operation);
        System.out.println("Fraction 2: " + num2);
        System.out.println("Numerator 1: " + newNume1);
        System.out.println("Denominator 1: " + newDeno1);
        System.out.println("Numerator 2: " + newNume2);
        System.out.println("Denominator 2: " + newDeno2);
    }

    if(operation.equals("+")){
        //adds numerators if denominators are the same
        if(newDeno1 == newDeno2){
            System.out.println("Answer is " + (newNume1 + newNume2) + "/" + + newDeno2);
        }
        else{
            int newDenom = newDeno1 * newDeno2;
            int multiplyNume = newNume1 * newDeno2;
            int multiplyNume2 = newNume2 * newDeno1;
            int finalNume = multiplyNume + multiplyNume2;
            System.out.println("Answer is " + finalNume + "/" + newDenom);
        }

    }

    if(operation.equals("-")){
        //subtracts numerators if denominators are the same
        if(newDeno1 == newDeno2){
            System.out.println("Answer is " + (newNume1 - newNume2) + "/" + + newDeno2);
        }
        else{
            int newDenom = newDeno1 * newDeno2;
            int multiplyNume = newNume1 * newDeno2;
            int multiplyNume2 = newNume2 * newDeno1;
            int finalNume = multiplyNume - multiplyNume2;
            System.out.println("Answer is " + finalNume + "/" + newDenom);
        }
    }

    if(operation.equals("*")){
        //multiplies numerators and denominators
        System.out.println("Answer is: " + newNume1 *  newNume2 + "/" + newDeno1 * newDeno2);

    }

    if(operation.equals("/")){
        System.out.println("Answer is: " + newNume1 *  newDeno2 + "/" + newDeno1 * newNume2);

        }

    }

}