groovy string contains

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11-03-2025

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The contains() method in Groovy is a powerful tool for string manipulation. This guide will explore its various uses, demonstrating how to efficiently check for substrings within strings, along with handling different scenarios and potential pitfalls. Understanding contains() is crucial for any Groovy developer working with text processing or data manipulation.

Understanding Groovy's contains() Method

At its core, Groovy's contains() method checks if a string contains a specific substring. It returns true if the substring is found, and false otherwise. This seemingly simple function offers flexibility and integrates well with Groovy's dynamic typing.

Basic Usage: Checking for Substrings

The most straightforward use of contains() involves directly comparing a string against a potential substring.

def myString = "This is a sample string"
boolean result = myString.contains("sample") // result will be true
println result

This code snippet demonstrates a basic contains() operation. The method seamlessly integrates into Groovy's syntax, providing a concise way to perform substring checks.

Case Sensitivity and its Implications

By default, contains() is case-sensitive. This means "Sample" will not be found in "This is a sample string". To perform a case-insensitive search, you can utilize Groovy's built-in string manipulation features, such as converting both the string and the substring to lowercase before comparison:

def myString = "This is a Sample string"
boolean result = myString.toLowerCase().contains("sample".toLowerCase()) // result will be true
println result

Converting to lowercase ensures that the comparison is not affected by differences in capitalization.

Handling Regular Expressions with contains()

Groovy's contains() method also supports regular expressions. This enables more sophisticated pattern matching beyond simple substring searches. However, note that it doesn't directly use regular expression objects; instead, it treats the argument as a regular expression string.

def myString = "This string contains multiple numbers: 123, 456, 789"
boolean result = myString.contains(/\d{3}/) // true because it contains at least one 3-digit number.
println result

This example uses a regular expression /\d{3}/ to check for the presence of at least one three-digit number within the string. Remember to escape special characters within regular expressions as needed (e.g., \., \*).

Finding the Index with indexOf()

While contains() tells you if a substring exists, it doesn't tell you where. For that, you'll need indexOf(). This method returns the starting index of the first occurrence of the substring, or -1 if it's not found.

def myString = "This is a test string"
int index = myString.indexOf("test") // index will be 10
println index

This is useful when you need to perform operations based on the substring's position within the larger string.

Dealing with Null or Empty Strings

Robust code should handle potential null or empty inputs. Always check for nulls before calling contains() to avoid NullPointerExceptions.

def myString = null
def substring = "test"

boolean result = myString == null ? false : myString.contains(substring) // Safe check for null
println result // Prints false

myString = ""
result = myString == null ? false : myString.contains(substring) //Handles empty string
println result // Prints false

This example uses a ternary operator for a concise null check. This prevents runtime errors and ensures the code's reliability.

Advanced Usage Scenarios and Best Practices

Let's explore scenarios where the power of contains() becomes particularly apparent.

Data Validation and Input Sanitization

contains() is frequently used to validate user input or data from external sources. You might check if a string contains invalid characters, specific keywords, or patterns that would indicate potential security issues.

def userInput = "This is; an invalid; string"
if (userInput.contains(";")) {
    println "Invalid characters found!"
}

This code snippet uses contains() to check for semicolons, which might be problematic in certain contexts.

String Manipulation and Transformation

You can combine contains() with other string manipulation methods to build more complex logic. For instance, you could extract substrings based on whether they contain a particular word or pattern.

def myString = "apple, banana, orange"
if (myString.contains("banana")) {
    def extracted = myString.substring(myString.indexOf("banana"), myString.indexOf("banana") + "banana".length())
    println extracted //Prints "banana"
}

This leverages indexOf() alongside contains() and substring() to extract a specific part of the string.

Working with Collections of Strings

The contains() method can be used effectively when dealing with lists or other collections of strings.

def stringList = ["apple", "banana", "orange"]
boolean containsBanana = stringList.any { it.contains("ana") } // true
println containsBanana

This demonstrates how to check if any string within a list contains a specific substring. Groovy's collection methods seamlessly integrate with contains().

Conclusion

Groovy's contains() method is a versatile and efficient tool for string manipulation. By understanding its usage, incorporating error handling, and combining it with other Groovy features, you can significantly enhance your ability to process and analyze text data. This method offers a balance of simplicity and power, making it a core component for any Groovy developer's toolkit. Remember to consider case sensitivity and the potential for regular expressions to fully leverage its capabilities.