# Conversion of Roman numerals to Arabic numerals (Java edition, more comprehensive)

Source: Internet
Author: User

I. Preface

My friend wanted to find a change on the Internet. However, after google and baidu, either the Java version is not found, or the considerations are not comprehensive enough. Therefore, I wrote it myself. If you have not fully considered it, I hope you can point it out. Next, go to the topic.

Ii. Rome digital rules

The number of Roman numerals indicates zero.

The basic method to represent numbers: Except for I, X, and C, after a large number, they are used as the Addons and before a large number as the subtraction. Generally, they write several basic Roman numbers together, it represents the sum of numbers.

1. Rewrite: III (3) XX (20) CC (200)

2. Left subtraction: IX (9) XL (40) CD (400)

3. Add right: VII (7) XI (11) LX (60)

4. Synthesis of the first three methods: XLV (L-X + V, 45) LXII (L + X + I, 62)

If you add a horizontal line above the number, the number is increased by 1000 times. (This rule is not implemented in the program because it is input)

Note:

1. I, X, and C cannot exceed three consecutive values on the right side of a large number (that is, when they are added together). Only one value can be used on the left side of a large number (that is, when the values are subtracted.

2. V, L, and D cannot be used on the left side of a large number (subtraction), but only on the right side of a large number (addition.

3. The left decimal places of V and X are only I; the left decimal places of L and C are only X; the left decimal places of D and m are only C.

Iii. Source Code

There are three classes: Roman, romanconverter, and romanexception.

Roman class: analyzes whether the input conforms to the rules of the Roman numerals, and converts the roman numerals to Arabic numerals. The Code is as follows:

Public class Roman <br/>{</p> <p> private final int num; // Arabic numerals (decimal) after conversion) </p> <p>/* <br/> private static int [] numbers = {1000,900,500,400,100, 90, <br/> 50, 40, 10, 9, 5, 4, 1 }; </p> <p> private static String [] letters = {"M", "CM", "D", "CD", "C ", "XC", <br/> "L", "XL", "X", "IX", "V", "IV", "I "}; <br/> */<br/> public Roman (String roman) throws RomanException <br/> {</p> <p> if (roman. le Ngth () = 0) // The input is null <br/>{< br/> throw new RomanException ("null character cannot be entered "); <br/>}</p> <p> roman = roman. toUpperCase (); // all Roman numerals are converted to uppercase </p> <p> int I = 0; // record the location of each character in the roman numerals <br/> int arabic = 0; // The converted arabic numerals </p> <p> while (I <roman. length () <br/>{< br/> char letter = roman. charAt (I); // character of the current position of the Roman numerals <br/> int number = letterToNumber (letter ); // convert the character to an Arabic number </p> <p> if (number <0) <br/>{< br/> throw new Roma NException ("excluding Roman numerals" + letter); <br/>}</p> <p> I ++; // move to the next position of the string </p> <p> if (I = roman. length () // The roman numerals have been processed <br/>{< br/> arabic + = number; <br/>}< br/> else <br/> {<br/> char nextLetter = roman. charAt (I); <br/> int nextNumber = letterToNumber (nextLetter); </p> <p> if (nextNumber> number) // The character at the backend is greater than that at the front end. <br/>{< br/> int result = nextNumber-number; </p> <p> if (result = 4 | result = 9 | result = 40 | result = 90 | result = 400 | result = 900) <br/>{< br/> arabic + = result; <br/> I ++; </p> <p> if (I = roman. length () // The roman numerals have been processed <br/>{< br/> break; <br/>}< br/> else <br/> {<br/> char afterNextLetter = roman. charAt (I); <br/> int afterNextNumber = letterToNumber (afterNextLetter); </p> <p> if (afterNextNumber> result) <br/>{< br/> throw new RomanException ("invalid roman numerals" + letter + nextLett Er + afterNextLetter ); <br/>}< br/> else <br/>{< br/> throw new RomanException ("invalid roman numerals" + letter + nextLetter ); <br/>}< br/> else <br/> {<br/> if (number = 5 | number = 50 | number = 500) & number = nextNumber) // V, L, and D are used on the right side of a large number (sum up). They are used more than once. <Br/>{< br/> throw new RomanException ("invalid roman numerals" + letter + nextLetter ); <br/>}</p> <p> if (number = nextNumber) <br/>{< br/> I ++; // check the next character again. </p> <p> if (I = roman. length () // The roman numerals have been processed <br/>{< br/> arabic + = number + nextNumber; <br/> break; <br/>}</p> <p> char afterNextLetter = roman. charAt (I); <br/> int afterNextNumber = letterToNumber (afterNextLetter); </p> <p> if (afterNextNumber> nextNumber) // I, X, and C are on the left side of the large number (that is, the subtraction time) use more than 2 <br/>{< br/> throw new RomanException ("invalid roman numerals" + letter + nextLetter + afterNextLetter ); <br/>}< br/> else if (afterNextNumber = nextNumber) // when all three characters are the same, for example, III <br/>{< br/> I ++; // you need to check the next character again. IIII may occur. (if this is not allowed, an exception should be thrown) </p> <p> if (I = roman. length () // The roman numerals have been processed <br/>{< br/> arabic + = number + nextNumber + afterNextNumber; <br/> break; <br/>}</p> <p> char afterNextNextLetter = roman. charAt (I); <br/> int afterNextNextNumber = letterToNumber (afterNextNextLetter); </p> <p> if (afterNextNextNumber = afterNextNumber) // IIII <br/> {<br/> throw new RomanException ("invalid roman numerals" + letter + nextLetter + afterNextLetter ); <br/>}< br/> else <br/> {<br/> arabic + = number; <br/> I = I-2; // roll back 2 characters (because 4 characters are considered) <br/>}< br/> else <br/> {<br/> arabic + = number + nextNumber; <br/>}< br/> else <br/> {<br/> arabic + = number; <br/>}</p> <p> if (arabic> 3999) <br/>{< br/> throw new RomanException ("the number cannot exceed 3999"); <br/>}</p> <p> num = arabic; </p> <p >}</p> <p>/** <br/> * convert Rome to Arabic numerals <br/> * @ param letter <br/> * @ return: normal Roman character, returns an Arabic number. Otherwise,-1 <br/> */<br/> private int letterToNumber (char letter) <br/>{< br/> switch (letter) <br/>{< br/> case 'I': return 1; <br/> case 'V': return 5; <br/> case 'X ': return 10; <br/> case 'l': return 50; <br/> case 'C': return 100; <br/> case 'D': return 500; <br/> case 'M': return 1000; <br/> default: return-1; <br/>}</p> <p> public int getNum () <br/>{< br/> return num; <br/>}</p> <p>

Romanconverter class -- main function entry class, used to test the conversion of Roman numerals. The Code is as follows:

Import java. util. topology; </p> <p> public class RomanConverter <br/> {<br/> public static void main (String [] args) <br/>{< br/> while (true) <br/>{< br/> System. out. println (); <br/> System. out. print ("Enter the roman numerals (Press Q to exit):"); </p> <p> export cin = new partition (System. in); <br/> String romanStr = cin. nextLine (); </p> <p> if (romanStr. equals ("q") | romanStr. equals ("Q") // exit the loop <br/>{< br/> break; <br/>}< br/> Roman roman = null; <br/> try <br/>{< br/> roman = new Roman (romanStr); <br/> System. out. println ("the converted Arabic numerals are:" + roman. getNum (); <br/>}< br/> catch (RomanException e) <br/>{< br/> System. out. println (e); <br/>}< br/> System. out. println ("welcome to use ^-^" again); <br/>}</p> <p>

Romanexception class-exception handling class. The Code is as follows:

Import java. util. topology; </p> <p> public class RomanConverter <br/> {<br/> public static void main (String [] args) <br/>{< br/> while (true) <br/>{< br/> System. out. println (); <br/> System. out. print ("Enter the roman numerals (Press Q to exit):"); </p> <p> export cin = new partition (System. in); <br/> String romanStr = cin. nextLine (); </p> <p> if (romanStr. equals ("q") | romanStr. equals ("Q") // exit the loop <br/>{< br/> break; <br/>}< br/> Roman roman = null; <br/> try <br/>{< br/> roman = new Roman (romanStr); <br/> System. out. println ("the converted Arabic numerals are:" + roman. getNum (); <br/>}< br/> catch (RomanException e) <br/>{< br/> System. out. println (e); <br/>}< br/> System. out. println ("welcome to use ^-^" again); <br/>}</p> <p>

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