Java String contains()

The Java String class contains() method searches the sequence of characters in this string. It returns true if the sequence of char values is found in this string otherwise returns false.

Signature

The signature of string contains() method is given below:

Parameter

sequence : specifies the sequence of characters to be searched.

Returns

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

Exception

NullPointerException : if the sequence is null.

Internal implementation

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

Here, the conversion of CharSequence takes place into String. After that, the indexOf() method is invoked. The method 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 indexOf() method returns -1. Therefore, after execution, the contains() method returns true when the indexOf() method returns a non-negative value (when the searched string is found); otherwise, the method returns false.

Java String contains() Method Example

FileName: ContainsExample.java

class ContainsExample{
public static void main(String args[]){
String name="what do you know about me";
System.out.println(name.contains("do you know"));
System.out.println(name.contains("about"));
System.out.println(name.contains("hello"));
}}

Test it Now

Output:

true
true
false

Java String contains() Method Example 2

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

FileName: ContainsExample2.java

public class ContainsExample2 {
	public static void main(String[] args) {
		String str = "Hello Javatpoint readers";
		boolean isContains = str.contains("Javatpoint");
		System.out.println(isContains);
		// Case Sensitive
		System.out.println(str.contains("javatpoint")); // false
	}
}

Output:

true
false

Java String contains() Method Example 3

The 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.

FileName: ContainsExample3.java

public class ContainsExample3 {	
	public static void main(String[] args) {		
		String str = "To learn Java visit Javatpoint.com";		
		if(str.contains("Javatpoint.com")) {
			System.out.println("This string contains javatpoint.com");
		}else
			System.out.println("Result not found");		
	}
}

Output:

This string contains javatpoint.com

Java String contains() Method Example 4

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

FileName: ContainsExample4.java

public class ContainsExample4 
{
// main method
public static void main(String argvs[])
{
String str = "Welcome to JavaTpoint!";

// comparing a string to null
if(str.contains(null))
{
System.out.println("Inside the if block");
}
else
{
System.out.println("Inside the else block");
}

}
}

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.lang.String.contains(String.java:2036)
	at ContainsExample4.main(ContainsExample4.java:9)

Limitations of the Contains() method

Following are some limitations of the contains() method:

The contains() method should not be used to search for a character in a string. Doing so results in an error.
The contains() method only checks for the presence or absence of a string in another string. It never reveals at which index the searched index is found. Because of these limitations, it is better to use the indexOf() method instead of the contains() method.

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