Java String.contains() Method: How to Check for Substrings – Practical Examples

Java String.contains() Method: How to Check for Substrings

The String.contains() method in Java determines whether a specified sequence of characters appears within a string. It returns true if the substring exists, otherwise false. Because the result is a boolean, it is commonly used directly in if statements.

Method Signature

public boolean contains(CharSequence s)

Parameters
s – The character sequence to search for.

Return Value
Returns true if this string contains the specified sequence; otherwise false.

Exceptions
Throws NullPointerException if s is null.

Practical Example

Below is a complete example that demonstrates common usage patterns and highlights case sensitivity.

public class SampleString {
    public static void main(String[] args) {
        String strSample = "This is a String contains Example";

        // Check for various substrings
        System.out.println("Contains 'ing': " + strSample.contains("ing"));
        System.out.println("Contains 'Example': " + strSample.contains("Example"));
        System.out.println("Contains 'example': " + strSample.contains("example")); // case-sensitive
        System.out.println("Contains 'is String': " + strSample.contains("is String"));
    }
}

Output:

Contains 'ing': true
Contains 'Example': true
Contains 'example': false
Contains 'is String': false

When to Use contains()

Use contains() whenever you need to verify the presence of a substring within a larger string. Common scenarios include:

• Validating user input (e.g., checking for prohibited words)
• Parsing log entries or configuration strings
• Implementing simple search features

Using contains() in Conditional Statements

The method integrates seamlessly with if/else logic. Here’s a concise example:

public class IfExample {
    public static void main(String[] args) {
        String text = "Java string contains If else Example";

        if (text.contains("example")) {
            System.out.println("The keyword :example: is found in the given string");
        } else {
            System.out.println("The keyword :example: is not found in the string");
        }
    }
}

Output:

The keyword :example: is not found in the string