Java contains() method

Hello all😀 I hope you are doing well. This is going to be a very short and very useful article. In this article I'll be writing about contains() method in Java. This method is very useful while you are doing competitive programming.

Let's begin...

contains()

This is a method of Java String class. This method returns a boolean value. This method checks if the specified substring is present in the given string. If substring is their then it returns true else it returns false. This method searches the sequence of characters in the given string. Remember this method is case-sensitive.

Syntax :-

stringVariableName.contains(substring);

Example :-

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains("main string"));
    }
}

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Remember it searches for the sequence of characters in the given string. This will be more clear from this example :-

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains("Hey string"));
    }
}

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This example will return true, we will pass an empty string in contains method but still it will return true because empty is a subset of any string.

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains(""));
    }
}

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If we pass null in the contains() it will throw a NullPointerException

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains(null));
    }
}

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There is one more way how you can use contains(), by passing string variable instead of passing a string itself.

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        String subStr = "I'm the main";
        System.out.println(str.contains(subStr));
    }
}

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We know that contains() method is case-sensitive, however there is a way you can check for the substring in the given string, using toUpperCase() or using toLowerCase() methods since both these methods and contains() method are the methods of same Java String class

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main STRING here!";
        System.out.println(str.toLowerCase().contains("the main string"));
    }
}

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Since contains() method returns boolean value we can use it with if else conditional statements

import java.util.Scanner;

public class Demo {
    public static void main(String[] args){
        String str = "Team Leader :- Ritvik Dubey";
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter team leader name");
        String subStr = sc.nextLine();
        sc.close();
        if(str.contains("Ritvik Dubey")) {
            System.out.println("Yes, team leader confirmed");
        }
        else {
            System.out.println("Team leader not confirmed");
        }
    }
}

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Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

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