Java中的正则表达式以查找字符串是否为带有尾随零的十进制数字格式

Question

I am reading a list of Strings, some of which are in the form of decimals and comapring them against another. Sadly, in the first list, I find that all decimal terms aka all the strings have an extra trailing zero. Thus, my .equals() function or .contains() function does not work.

List 1 : 134.20, 16, abacus, 44.10, 12/2/2013, 4, 45.220
List 2 : 134.2,  16, abacus, 44.2,  12/2/2013, 4, 45.22

How do I add a trailing zero in List 2? Is there way to use regex or so to somehow remove the trailing zero if present?

Conversely, can I remove the trailing zero in List 1?

Answer 1

To remove trailing zeroes from decimals:

String zeroless = str.replaceAll("(\\b\\d+\\.[1-9]*)0+\\b", "$1");

To add trailing a zero where there isn't one:

String zeroless = str.replaceAll("(\\b\\d+\\.\\d*)[1-9]\\b", "$10");

An important part of this regex is the wrapping with \\\\b - a "word boundary".

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I'm not sure how useful either of these will be. If you're try to see if a particular decimal is in a string, remove the trailing zeroes from it, then search for it in your input with optional trailing zeros, like this:

String num;  // eg 123.456
if (input.matches(".*\\b" + num.replace(".", "\\.").replaceAll("0+$", "") + "0*\\b.*")) {
    // input contains the number
}

Answer 2

This will get read of all unneccessary trailing zeroes:

str = str.replaceAll("(\\d+\\.\\d+?)0+", "$1");

Examples:

123.456000 --> 123.456
123.000    --> 123.0

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Update: In the comment you asked how to unconditionally append a zero. This is how you do it:

str = str.replaceAll("(\\d+\\.\\d+)", "$10");

Answer 3

You could use String.format() to get them all to how ever many decimal places.

String yourValue = "4.4";
int range = 3;
String zeros = String.format("%."+range+"f", Float.parseFloat(yourValue)); // 3 decimal places
System.out.println(zeros); // prints 4.400

Change range as needed for different number of decimal places needed.

Alternatively, if you are just using them to check if they are equal/greater/less then why don't you just parse the string as Double (or other suitable object) and then compare the Doubles then "2.2" == "2.20" anyway and you can use the already defined equals() and compareTo() for those objects

Answer 4

You should be using BigDecimal to compare decimal values, not Strings at all. Get rid of the regular expression, use new BigDecimal(String), set the scale you want, and then use compareTo().