Java String contains()

In this article, we will look at contains() method from string class in java, what is it used for, syntax, return value with example programs.

Overview
Java string contains() method is used to check if a string contains a sequence of characters or not.
Syntax
contains() method accepts an argument of type java.lang.CharSequence, which represents a sequence of characters.
CharSequence is an interface, which is implemented by String, StringBuffer and StringBuilder classes.

Thus, argument of contains() method may be of any of these types. Its signature is

Return Value
contains() returns true or false values depending on the sequence of characters in the argument object occur in the string or not.

It returns

Remember that the characters should be in the same sequence as the argument.

Java documentation for contains() states,

Returns true if and only if this string contains the specified sequence of char values.

String contains() example
Below is an example of string contains() method

String source = "codippa.com";
String search = ".com";
System.out.println(source.contains(search)); // true

String contains() implementation
contains() method internally invokes another string class indexOf() method, which returns the first index of matching string.
indexOf() returns -1, if the supplied string cannot be found in the source string.

Thus, contains() simply compares the value returned by indexOf() with 0.
If the value from indexOf() is greater than or equal to 0, this means that the string contains characters.

Below is the source code of contains()

public boolean contains(CharSequence s) {
  return indexOf(s.toString()) >= 0;
}

String contains() case sensitive
contains() performs case sensitive comparison. This means that the string to be checked should exist in the same case in source string, otherwise contains() will return false. Example,

String source = "codippa.com"; 
String search = ".Com"; 
System.out.println(source.contains(search)); // false

Thus, the comparison by contains() is not insensitive.

Hope the article on Java string contains() method was useful.