How to Check if String Contains Substring in Java

In Java, you can check if a string contains a substring using the contains() method of the String class. It returns true if the substring is found and false otherwise.

Syntax

The contains() method is called on a string object and takes one argument: the substring to search for. It returns a boolean value.

• string.contains(substring): Returns true if substring is inside string.

java

boolean result = string.contains(substring);

Example

This example shows how to use contains() to check if a string has a certain substring and prints the result.

java

public class Main {
    public static void main(String[] args) {
        String text = "Hello, welcome to Java programming!";
        String word1 = "Java";
        String word2 = "Python";

        System.out.println("Does the text contain '" + word1 + "'? " + text.contains(word1));
        System.out.println("Does the text contain '" + word2 + "'? " + text.contains(word2));
    }
}

Output

Does the text contain 'Java'? true
Does the text contain 'Python'? false

Common Pitfalls

One common mistake is confusing contains() with case-insensitive search. The contains() method is case-sensitive, so "java" and "Java" are different.

To check ignoring case, convert both strings to the same case first.

java

public class Main {
    public static void main(String[] args) {
        String text = "Hello, welcome to Java programming!";
        String search = "java";

        // Wrong: case-sensitive check
        System.out.println(text.contains(search)); // false

        // Right: convert both to lower case
        System.out.println(text.toLowerCase().contains(search.toLowerCase())); // true
    }
}

Output

false
true

Quick Reference

Method	Description	Returns
contains(CharSequence s)	Checks if string contains the sequence s	boolean (true/false)
toLowerCase()	Converts string to lower case	String
toUpperCase()	Converts string to upper case	String

Key Takeaways

Use string.contains(substring) to check if a substring exists in a string.

contains() is case-sensitive; convert strings to lower or upper case for case-insensitive checks.

The method returns a boolean: true if found, false if not.

Always handle null strings carefully to avoid errors when calling contains().