Java String contains() method with example

java.lang.String.contains() method searches the sequence of characters in the given string. It returns true if sequence of char values are found in this string otherwise returns false. 
Implementation of this method : 

public boolean contains(CharSequence sequence)
{
   return indexOf(sequence.toString()) > -1;
}

Here conversion of CharSequence to a String takes place and then indexOf method is called. The method indexOf returns O or higher number if it finds the String, otherwise -1 is returned. So, after execution, contains() method returns true if sequence of char value exists, otherwise false. 
Syntax : 

public boolean contains(CharSequence sequence)
Parameter : sequence : This is the sequence of 
characters to be searched.
Exception :
NullPointerException : If seq is null

Example : To check whether the charSequence is present or not. 

Java

// Java program to demonstrate working
// contains() method
class Gfg {

    // Driver code
    public static void main(String args[])
    {
        String s1 = "My name is GFG";

        // prints true
        System.out.println(s1.contains("GFG"));

        // prints false
        System.out.println(s1.contains("geeks"));
    }
}

Output:

true
false

Example : Case sensitive method to check whether given CharSequence is present or not. 

Java

// Java code to demonstrate case
// sensitivity of contains() method
class Gfg1 {

    // Driver code
    public static void main(String args[])
    {
        String s1 = "Welcome! to GFG";

        // prints false
        System.out.println(s1.contains("Gfg"));

        // prints true
        System.out.println(s1.contains("GFG"));
    }
}

Output:

false
true

Further Thoughts :

• This method does not work to search for a character.
• This method does not find index of string if it is not present.
• For above two functionalities, there is a better function String indexOf