String contains() method - Syntax and Examples

Learn about the Java String `contains()` method. This tutorial explains the syntax, parameters, return value, and provides practical examples of how to use it.

This reference explains String contains() method - Syntax and Examples through its syntax, examples and boundaries. Use the linked course lessons when the surrounding Java concepts are unfamiliar.

The contains() method in Java is a handy tool for checking if one string exists within another. Think of it like searching for a specific word in a book – the contains() method tells you whether that word is present or not.

public boolean contains(CharSequence s)

The contains() method returns true if the specified character sequence is found within this string; otherwise, it returns false.

This example demonstrates how to use contains() to check if a simple string exists within another string. We'll look for the word 'Java'.

public class Main {
  public static void main(String[] args) {
    String text = "This is a Java tutorial.";
    boolean containsJava = text.contains("Java");
    System.out.println(containsJava);
  }
}

true

In this example, the text variable holds a string. The contains() method checks if 'Java' is present within text. Because it is, the method returns true and that value gets printed to the console.

The contains() method is case-sensitive. This example shows what happens when we search for a string with different capitalization.

public class Main {
  public static void main(String[] args) {
    String text = "This is a Java tutorial.";
    boolean containsJavaLower = text.contains("java");
    System.out.println(containsJavaLower);
  }
}

false

Here, we're searching for 'java' (lowercase). Because the original string contains 'Java' (uppercase), the method returns false.

The contains() method can also accept a character array as input. This example demonstrates that use case.

public class Main {
  public static void main(String[] args) {
    String text = "Hello World";
    char[] chars = {'H', 'e'}; //Character array to search for.
    boolean containsChars = text.contains(chars);
    System.out.println(containsChars);
  }
}

true

We're searching the string text, for a character array that represents 'He'. As it is present in the text, the method returns true.

This example explores what happens when we attempt to search for an empty string within another string. An empty string is represented by "".

public class Main {
  public static void main(String[] args) {
    String text = "Hello World";
    boolean containsEmpty = text.contains("");
    System.out.println(containsEmpty);
  }
}

true

The method always returns true when searching for an empty string because every string contains a zero-length sequence at the beginning and after the last character.

This example demonstrates how to use contains() with a StringBuilder object.

public class Main {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Java is awesome");
        boolean containsAwesome = sb.contains("awesome");
        System.out.println(containsAwesome);
    }
}

true

The contains() method can be used with a StringBuilder object like any other CharSequence.

Check the example’s types, inputs and documented behavior before copying it into an application. Some APIs require external libraries, files or platform services; consult their setup notes.

Related explanations: Java Data Types - Primitive and Non-Primitive, Java Class - Blueprint of Objects, Exceptions in Java Introduction.

Supporting documentation: Official Java learning guide.