Java String contains() method
Syntax and Examples

Introduction

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.

Syntax

public boolean contains(CharSequence s)

Parameters

Parameter	Description
s	The sequence of characters to search for within this string. It can be a String, Character Array or any other CharSequence implementation.

Return Value

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

Examples

Example 1: Basic String Search

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.

Example 2: Case Sensitivity

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.

Example 3: Using a Character Array

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.

Example 4: Checking for Empty String

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.

Example 5: Using StringBuilder

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.