将字符串表示转换为最小数字对象

Question

Having a String representation of a number(no decimals), what's the best way to convert it to either one of java.lang.Integer or java.lang.Long or java.math.BigInteger ? The only condition is that the converted type should be of minimal datatype required to hold the number.

I've this current implementation that works fine, but I would like to know if there's a better code without exception handling.

package com.stackoverflow.programmer;

import java.math.BigInteger;

public class Test {
    public static void main(String[] args) {

        String number = "-12121111111111111";
        Number numberObject = null;
        try {
            numberObject = Integer.valueOf(number);
        } catch (NumberFormatException nfe) {
            System.out.println("Number will not fit into Integer type. Trying Long...");
            try {
                numberObject = Long.valueOf(number);
            } catch (NumberFormatException nfeb) {
                System.out.println("Number will not fit into Long type. Trying BigInteger...");
                numberObject = new BigInteger(number);
            }
        }
        System.out.println(numberObject.getClass() + " : "
                + numberObject.toString());
    }
}

Answer 1

From what you said, here is what I would have done:

import java.math.BigInteger;
import java.util.Arrays;
import java.util.List;

public class TestSO09_39463168_StringToMinimalNumber {

    public static void main(String[] args) {
        List<String> strNumbers = Arrays.asList("0", //int
                "123", //int
                "-456", //int
                "2147483700", // Long
                "-2147483700", // Long
                "9223372036854775900", //BigInt
                "-9223372036854775900" //BigInt
                );

        for(String strNumber : strNumbers){
            Number number = stringToMinimalNumber(strNumber);
            System.out.println("The string '"+strNumber+"' is a "+number.getClass());
        }

    }

    public static Number stringToMinimalNumber(String s){
        BigInteger tempNumber = new BigInteger(s);

        if(tempNumber.compareTo(BigInteger.valueOf(Long.MAX_VALUE)) > 0 || tempNumber.compareTo(BigInteger.valueOf(Long.MIN_VALUE)) < 0){
            return tempNumber;
        } else if(tempNumber.compareTo(BigInteger.valueOf(Integer.MAX_VALUE)) > 0 || tempNumber.compareTo(BigInteger.valueOf(Integer.MIN_VALUE)) < 0){
            return tempNumber.longValue(); //Autobox to Long
        } else {
            return tempNumber.intValue(); //Autobox to Integer
        }

    }

}

You must use a temporary BigInteger, or else you'll end up with lazarov's solution, which is correct, but you can't really do something like that for reason mentionned in the comments.

Anyway, every BigInteger (the ones that are not returned) will be garbage collected. As for autoboxing, I don't think it's that of a bad thing. You could also make " BigInteger.valueOf(Long.MAX_VALUE)) " as a constant. Maybe the compiler or the JVM will do this on its own.

I'm not really sure of how efficient it is, and using only BigInteger might be a good idea (as Spotted did), because I serioulsy doubt it would really improve the rest of your code to use the right size, and it might even be error prone if you try to use these Numbers with each other ... But again, it all depend on what you need. (and yes, using Exception as flow control is a really bad idea, but you can add a try catch on the BigInteger tempNumber = new BigInteger(s); to throw your own exception if s is not a number at all)

For recreational purpose, I have made the solution without using a BigInteger, and only with String parsing (this is still not what I recommand to do, but it was fun :)

public static final String INT_MAX_VALUE = "2147483647";
public static final String LONG_MAX_VALUE = "9223372036854775807";

public static Number stringToMinimalNumberWithoutBigInteger(String numberStr){
    //Removing the minus sign to test the value
    String s = (numberStr.startsWith("-") ? numberStr.substring(1,numberStr.length()) : numberStr);

    if(compareStringNumber(s, LONG_MAX_VALUE) > 0){
        return new BigInteger(numberStr);
    } else if(compareStringNumber(s, INT_MAX_VALUE) > 0){
        return new Long(numberStr);
    } else {
        return new Integer(numberStr);
    }
}

//return postive if a > b, negative if a < b, 0 if equals;
private static int compareStringNumber(String a, String b){
    if(a.length() != b.length()){
        return a.length() - b.length();
    }
    for(int i = 0; i < a.length(); i++){
        if( a.codePointAt(i) != b.codePointAt(i) ){ //Or charAt()
            return a.codePointAt(i) - b.codePointAt(i);
        }
    }
    return 0;
}

Answer 2

Please don't use exceptions for handling flow control, this is a serious anti-pattern (also here ).

As you mentionned in the comments, the real thing you've been asked is to convert a List<String> into a List<Number> . Also, if I understand correctly, you know that:

• You should encounter only numbers without decimals
• The biggest value you can encounter is possibly unbound

Based on that, the following method will do the job in a more clever way:

private static List<Number> toNumbers(List<String> strings) {
    return strings.stream()
                  .map(BigInteger::new)
                  .collect(Collectors.toList());
}

Eidt: if you're not very familiar with the stream concept, here's the equivalent code without streams:

private static List<Number> toNumbers(List<String> strings) {
    List<Number> numbers = new ArrayList<>();
    for (String s : strings) {
        numbers.add(new BigInteger(s));
    }
    return numbers;
}

Answer 3

Well if you want to do it "by hand" try something like this:

We define the max values as strings :

String intMax = "2147483647";
String longMax = "9223372036854775807";

and our number:

String ourNumber = "1234567890"

Now our logic will be simple : We will check lenghts of strings firstly

1. If our numbers length < int max length : IT IS INT

2. If our numbers length == int max length : Check is it INT or LONG

3. If our numbers length > int max length :

   3.1 If our numbers length < long max length : IT IS LONG

   3.2 If our numbers length == long max length : Check is it LONG or BIG INTEGER

   3.3 If our numbers length > long max length : IT IS BIG INTEGER

The code should look something like this (I have not tried to compile it may have syntax or other errors) :

if(ourNumber.lenght() < intMax.length ){
    System.out.println("It is an Integer");
} else if(ourNumber.lenght() == intMax.length){
    // it can be int if the number is between 2000000000 and 2147483647
            char[] ourNumberToCharArray = ourNumber.toCharArray();
            char[] intMaxToCharArray = intMax.toCharArray();
            int diff = 0;
            for(int i = 0; i < ourNumberToCharArray.length; i++) {  
                diff  = Character.getNumericValue(intMaxToCharArray[i]) - Character.getNumericValue(ourNumberToCharArray[i]);
                if(diff > 0) { 
                    System.out.println("It is a Long");
                    break;                  
                } else if(diff < 0) {
                    System.out.println("It is an Integer");
                        break;
                }
            }
            if(diff == 0){
              System.out.println("It is an Integer");  
            }   
} else { 
    if(ourNumber.lenght() < longMax.length()) {
        System.out.println("It is a Long");
    } else if(ourNumber.lenght() == longMax.length()){
            char[] ourNumberToCharArray = ourNumber.toCharArray();
            char[] longMaxToCharArray = longMax.toCharArray();
            int diff = 0;
            for(int i = 0; i < ourNumberToCharArray.length; i++) {  
                diff  = Character.getNumericValue(longMaxToCharArray[i]) - Character.getNumericValue(ourNumberToCharArray[i]);
                if(diff > 0) { 
                    System.out.println("It is a BigInteger");
                    break;                  
                } else if(diff < 0) {
                    System.out.println("It is a Long");
                        break;
                }
            }   
            if(diff == 0){
              System.out.println("It is a Long");  
            }   
    } else { 
        System.out.println("It is a BigInteger");
    }
}

Then logic that checks if the numbers match or not is the same in both cases you can but it in a function for example.