Valid Number Problem in Java

The "Valid Number" problem involves determining whether a given string represents a valid numerical value. This is a common problem in software development, particularly when parsing input data that should represent numbers.

Problem Statement

Given a string s, determine if it represents a valid number. Valid numbers include integers, floating-point numbers, and scientific notation. Examples of valid numbers are:

• "0"
• "0.1"
• "-3.14"
• "2e10"
• "-2.3E-10"
• "+6.78"

Examples of Invalid Numbers

• "abc"
• "1a"
• "1e"
• "e3"
• "99e2.5"

Approach

To solve this problem, we need to check if the given string adheres to the rules for valid numbers. The rules are as follows:

1. The string may start with a sign (+ or -).
2. The string may contain digits.
3. The string may contain a decimal point.
4. The string may contain an exponent part, denoted by e or E, followed by an optional sign and digits.

We can use a finite state machine (FSM) or a regular expression to validate the string. In this section, we will use a regular expression for simplicity.

File Name: ValidNumber.java

Explanation

The regular expression ^[+-]?((\d+(\.\d*)?)|(\.\d+))(e[+-]?\d+)?$ is used to match valid numbers by following specific rules: ^[+-]? matches an optional sign at the beginning, (\d+(\.\d*)?)|(\.\d+) matches digits with an optional decimal point or a decimal point followed by digits, and (e[+-]?\d+)?$ matches an optional exponent part consisting of e or E, an optional sign, and digits.

The isValidNumber() method first checks if the input string is null or empty, then trims it and uses the regular expression to validate the trimmed string, returning true if it matches and false otherwise. The main() method demonstrates the usage of isValidNumber() with various test cases, printing out whether each string represents a valid number.