Java check if string is number or string

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Java check if string is number or string

A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi. Andrzej Lach wrote: I also got here from google. Good pattern but needs an update. Jesper's Blog - Pluralsight Author Page. Your easiest solution would be to use Integer. Dennis Deems wrote: Your easiest solution would be to use Integer.

Mike Simmons wrote: The religiously absolutist idea that exceptions can only be used to indicate errors in the application as opposed to input data can be pointlessly counterproductive, as not all libraries are actually designed this way. Winston Gutkowski wrote: If this was a file as opposed specifically to user input, I doubt you would be advocating this style, so at best it works in situations where you know that it's the only way you're going to receive numbers.

Winston Gutkowski wrote: The advantage of a regex or indeed Scanner is that it can be applied to any InputStream, so if you're testing, you can change your mode of input; and if you wrap it in a decent utility method, who cares how complicated the actual code is?

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For testing I'd just write a method that takes a String as input, and I can easily call it with any String input I want. Also, how do you apply a regex to an InputStream? The two ways I can think of are to use a Scanner, or read the InputStream into a String, neither of which sounds like what you're talking about. Maybe I'm overlooking a method here?

Winston Gutkowski wrote: You may have seen my rant a while back about methods that return booleans when in fact one that returns an index might make a better building block. Or indeed, provide both. I lost BTW; at least in terms of votes. Mike Simmons wrote: Sure, I was one of the main people arguing with you. Dennis was there too. I really enjoy our little 'contretemps'; and I've learnt quite a lot from you. Not least, how not to be quite such an old fart. Mike Simmons wrote: My preference for Scala's Option type is coloring my thinking here Mike Simmons wrote: Scala's approach is to create a data wrapper representing a nullable type like a container with 0 or 1 element The syntax is weird at first, but very useful Mike Simmons wrote: Cool.

However I was just looking over some Scala APIs; I suspect you won't be as thrilled with the plethora of arcanely-named methods available on all the collection-type classes.

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Winston Gutkowski wrote:. Mike Simmons wrote: And my dislike of returning null is strong enough that if someone wants to do it, I'd rather force them to do it explicitly with parseInt s, null rather than someone picking up that behavior accidentally and forget to check the return value.

Forum: Beginning Java. How to check if String value is numeric. Bob Robertson.So it will show the output as. Check if string contains valid number example. This example shows how to check if string contains valid number. Double and Integer wrapper classes.

Output would be. Want to learn quickly? Try one of the many quizzes. More than Java questions with detailed answers. Yes, I want to learn Java quickly. You may also like. Java String Examples Java String to java. Date Example December 1, Java String Array Length Example.

Check if a given string is a valid number (Integer or Floating Point) in Java

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This example shows how to check if string contains valid number or not using parseDouble and parseInteger methods of Double and Integer wrapper classes.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I'm hoping there's something in the same conceptual space as the old VB6 IsNumeric function? Of course, you can negate this if you need to. For example, to implement the IsNumeric example you gave:. Only works if the string only contains numeric characters, else it returns NaN. Empty strings may be a little counter-intuitive.

java check if string is number or string

If you're just trying to check if a string is a whole number no decimal placesregex is a good way to go. Other methods such as isNaN are too complicated for something so simple. Note that! The problem with parseFloat is that it will return a number if the string contains any number, even if the string doesn't contain only and exactly a number:. The problem with Number is that it will return a number in cases where the passed value is not a number at all!

The problem with rolling your own regex is that unless you create the exact regex for matching a floating point number as Javascript recognizes it you are going to miss cases or recognize cases where you shouldn't. And even if you can roll your own regex, why? There are simpler built-in ways to do it. However, it turns out that Number and isNaN does the right thing for every case where parseFloat returns a number when it shouldn't, and vice versa. So to find out if a string is really exactly and only a number, call both functions and see if they both return true:.

The accepted answer for this question has quite a few flaws as highlighted by couple of other users. Try the isNan function :. This function is different from the Number specific Number. However, even this one is far from complete. Leading zeros are not handled here, but they do screw the length test. I have tested and Michael's solution is best. Vote for his answer above search this page for "If you really want to make sure that a string" to find it. In essence, his answer is this:.

Many of the other solutions fail for these edge cases: ' ', null, "", true, and [].Introduction — This tutorial first defines a palindrome. It then provides a short algorithm to determine whether a sequence of characters or numbers is a palindrome.

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Lastly, it provides the Java code for determining whether the given number or string is a palindrome or not, without using inbuilt String functions in Java, along with explanation of the code. What is a Palindrome A palindrome is a word, phrase, number or a sequence of characters which reads the same when read from either directions. Examples of palindromes — Noon, radar, madam, redder. Algorithmic steps to determine whether the given number or a string is a palindrome Palindrome determination algorithm consists of 3 simple steps — STEP 1: Reverse the given number or string.

STEP 2: Compare the original number or string with the reversed one. STEP 3: If the original and reversed match then it is a palindrome, else it is not a palindrome. Java code to check if the given number or string is a palindrome Java code to check if the given number or string is a palindrome package com. Java code to check if the given number or string is a palindrome.

Sign-Up for JavaBrahmanWeekly! Get weekly summary of new articles in your inbox!In Set 1we have discussed general approach to check whether a string is a valid number or not. In this post, we will discuss regular expression approach to check for a number.

java check if string is number or string

For floating point number : Below is the regular definition for a floating point number. This article is contributed by Gaurav Miglani.

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java check if string is number or string

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Writing code in comment? Please use ide. Check if a given string is a valid number Integer or Floating Point SET 1 Basic approach Check if a given string is a valid number Integer or Floating Point in Java SET 2 Regular Expression approach Get the first letter of each word in a string using regex in Java Reverse words in a given String in Java Program to implement FLAMES game Split the given string into Primes : Digit DP Find lexicographically smallest string in at most one swaps Remove odd frequency characters from the string Longest palindrome formed by concatenating and reordering strings of equal length Longest Palindrome in a String formed by concatenating its prefix and suffix Minimum letters to be removed to make all occurrences of a given letter continuous Count maximum occurrence of subsequence in string such that indices in subsequence is in A.

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Matcher; import java.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here.

Java Replacing & Removing Characters in Strings

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With Apache Commons Lang 3. You can also use StringUtils. Another way is to use NumberUtils. The linked javadocs contain detailed examples for each method. This is generally done with a simple user-defined function i. Roll-your-own "isNumeric" function. However, if you're calling this function a lot, and you expect many of the checks to fail due to not being a number then performance of this mechanism will not be great, since you're relying upon exceptions being thrown for each failure, which is a fairly expensive operation.

An alternative approach may be to use a regular expression to check for validity of being a number:.

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Be careful with the above RegEx mechanism, though, as it will fail if you're using non-Arabic digits i. Thanks to OregonGhost for pointing this out! Or even another alternative is to use Java's built-in java. NumberFormat object to see if, after parsing the string the parser position is at the end of the string. If it is, we can assume the entire string is numeric:. As CraigTP had mentioned in his excellent answer, I also have similar performance concerns on using Exceptions to test whether the string is numerical or not.

So I end up splitting the string and use java. According to the JavadocCharacter. Performance-wise, I think a simple N number of comparisons where N is the number of characters in the string would be more computationally efficient than doing a regex matching. Below is the updated code that correctly validates decimal numbers according to the default locale used in your system, with the assumption that decimal separator only occur once in the string.

Google's Guava library provides a nice helper method to do this: Ints. You use it like Integer. I haven't benchmarked it. Looking at the source code there is some overhead from a lot of sanity checking but in the end they use Character.

There is no exception handling overhead under the covers in their implementation. Do not use Exceptions to validate your values. Use Util libs instead like apache NumberUtils:. Please notice that, if your string starts with an 0, NumberUtils will interpret your value as hexadecimal.Learn Java by Examples. Everything you want to know about Java. Pin It.

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