String contains() Method in Java — Check Substring with Example

String contains() Method in Java — Check Substring with Example

1. Introduction 

The contains() method is a useful utility provided by the String class in Java. It allows you to check if a particular substring is present within a given string. This method returns a boolean value, true if the substring is found, and false otherwise. The contains() method is case-sensitive, meaning it considers the exact case of the characters in the substring.

2. Syntax 

The syntax for the contains() method is as follows:

java
public boolean contains(CharSequence sequence)

3. Parameters

• sequence: The sequence of characters to be checked for existence in the string.

4. Return Value

• true if the specified substring is present in the string.
• false if the specified substring is not found in the string.

5. Example
Let's see a code example to understand the usage of the contains() method:

java
public class StringContainsExample {
    public static void main(String[] args) {
        String mainString = "Hello, World!";
        String substring1 = "Hello";
        String substring2 = "world"; // Note the lowercase 'w'

        // Check if the mainString contains substring1
        boolean containsSubstring1 = mainString.contains(substring1);
        System.out.println("Contains 'Hello': " + containsSubstring1); // Output: Contains 'Hello': true

        // Check if the mainString contains substring2
        boolean containsSubstring2 = mainString.contains(substring2);
        System.out.println("Contains 'world': " + containsSubstring2); // Output: Contains 'world': false
    }
}

6. Explanation

• In this example, we have a mainString with the value "Hello, World!".
• We then define two substrings, substring1 with the value "Hello" and substring2 with the value "world".
• We use the contains() method to check if mainString contains each of the substrings.
• The first check (mainString.contains(substring1)) returns true because "Hello" is present in mainString.
• The second check (mainString.contains(substring2)) returns false because "world" (with a lowercase 'w') is not present in mainString.
• It is important to note that the contains() method is case-sensitive. If you need to perform a case-insensitive check, you can convert both the main string and the substring to lowercase or uppercase before calling the contains() method.

7. Conclusion 

The contains() method in Java is a convenient way to check if a specific substring exists within a given string. It is a simple yet powerful tool for string manipulation and searching. Remember to consider the case-sensitivity of the method when using it in your applications.