Java String.contains() Method

In Java, the String.contains() method searches the sequence of characters in the given string. It returns a boolean value: true if the string contains the specified sequence of characters, false otherwise.

Syntax:

Parameter

sequence: Specifies the sequence of characters to be searched.

Returns: true if the sequence of char value exists, otherwise false.

Exception: The method throws NullPointerException if the sequence is null.

This method is particularly useful in a variety of scenarios, such as validating user input, searching keywords in text, filtering data, and more. Its simplicity and readability make it a preferred choice for basic substring checks.

To read more Java String

Internal Implementation

Here, the conversion of CharSequence takes place into String. After that, the String.indexOf() method is invoked. The method String.indexOf() either returns 0 or a number greater than 0 in case the searched string is found.

However, when the searched string is not found, the String.indexOf() method returns -1. Therefore, after execution, the String.contains() method returns true when the String.indexOf() method returns a non-negative value (when the searched string is found); otherwise, the method returns false.

Case Sensitivity

By default, the String.contains() method is case-sensitive. It means that uppercase and lowercase letters are treated differently. For instance:

To perform a case-insensitive search, we can convert both the source string and the search string to the same case using methods like toLowerCase() or toUpperCase():

Example: String.contains() Method

Output:

true
true
false

Example: String.contains() Method

The String.contains() method searches case-sensitive char sequence. If the argument is not case sensitive, it returns false. Let's see an example.

Output:

true
true

Example: String.contains() Method

The String.contains() method is helpful to find a char-sequence in the string. We can use it in the control structure to produce the search-based result. Let's see an example.

Output:

This string contains TpointTech.com

Example: String.contains() Method

The String.contains() method raises the NullPointerException when one passes null in the parameter of the method. The following example shows the same.

Output:

Runtime Error:
Exception in thread "main" java.lang.NullPointerException
	at java.base/java.lang.String.contains(String.java:2058)
	at Main.main(Main.java:7)

Use Cases

The String.contains() method finds application in various scenarios, including:

• Search Operations: It is commonly used to search for specific substrings within a larger string, such as parsing user input or searching for keywords in text.
• Filtering Data: When processing collections of strings, String.contains() can help filter out elements based on certain criteria.
• Input Validation: In user input validation, String.contains() can be employed to ensure that certain substrings are present or absent.