Java String contains() Method

What You’ll Learn

The contains() method answers a simple question: “Does this string include that substring?” It returns true or false, which makes it perfect for validation, filtering, and readable if statements.

Definition and Usage

In Java, contains(CharSequence sequence) is defined on java.lang.String. It searches the entire string for the first occurrence of the argument as a contiguous block of characters. If "Hello, Java Programming!" contains "Java", the method returns true.

Unlike startsWith() or endsWith(), contains() matches the substring anywhere in the text—beginning, middle, or end.

📝 Syntax

The contains() method is declared in the String class:

public boolean contains(CharSequence sequence)

Parameters

• sequence — the substring to search for. Must not be null.

Return Value

Returns true if sequence appears as a substring; otherwise false.

Exceptions

Throws NullPointerException if sequence is null.

Examples Gallery

These programs run in Java 8+. They show a basic match, a failed search, case rules, case-insensitive validation, and comparison with indexOf().

public class StringContainsExample {
    public static void main(String[] args) {
        String text = "Hello, Java Programming!";

        boolean containsJava = text.contains("Java");

        System.out.println("Contains 'Java'? " + containsJava);
    }
}

Contains 'Java'? true

public class NotFoundDemo {
    public static void main(String[] args) {
        String course = "Java Programming";

        System.out.println("Contains Python? " + course.contains("Python"));
        System.out.println("Contains Prog?   " + course.contains("Prog"));
    }
}

Contains Python? false
Contains Prog?   true

public class CaseSensitive {
    public static void main(String[] args) {
        String title = "Learn Java Today";

        System.out.println("Contains 'Java'? " + title.contains("Java"));
        System.out.println("Contains 'java'? " + title.contains("java"));
    }
}

Contains 'Java'? true
Contains 'java'? false

public class IgnoreCaseSearch {
    public static boolean containsIgnoreCase(String text, String keyword) {
        return text.toLowerCase().contains(keyword.toLowerCase());
    }

    public static void main(String[] args) {
        String input = "I love JAVA programming";

        System.out.println(containsIgnoreCase(input, "java"));
    }
}

true

public class ContainsVsIndexOf {
    public static void main(String[] args) {
        String url = "https://codetofun.com/java";

        boolean hasJava   = url.contains("/java");
        int javaPosition  = url.indexOf("/java");

        System.out.println("contains:  " + hasJava);
        System.out.println("indexOf:   " + javaPosition);
    }
}

contains:  true
indexOf:   23

🚀 Common Use Cases

• Input validation — reject emails without @ or passwords missing required symbols.
• Keyword filtering — flag messages that include banned or required words.
• URL and path checks — test whether a link includes https:// or a route segment.
• Simple search — highlight rows in a list when the user’s query appears in the text.
• Feature toggles in text — branch logic when configuration strings include a token.

📝 Notes

• contains() is case-sensitive unless you normalize case first.
• It matches substrings anywhere—not necessarily whole words.
• contains("") always returns true for any string.
• The parameter type is CharSequence, so StringBuilder values work too.
• For “starts with” or “ends with” checks, use startsWith() or endsWith() instead.

⚡ Optimization

contains() is optimized for general substring search and is the right default for most applications. If you call the same check repeatedly in a hot loop, store the boolean result in a local variable. For very large texts and advanced pattern matching, regular expressions or specialized libraries may be appropriate—but start with contains() for simple literal searches.

💡 Best Practices