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Java String Methods

Java provides a wide range of methods to manipulate and handle strings effectively. These methods are part of the String class, which is included in the java.lang package.

Key Topics

1. length()

Returns the length of the string.

Example

public class StringLengthExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Length: " + str.length());
    }
}

Output:

Length: 13

2. charAt(int index)

Returns the character at the specified index.

Example

public class StringCharAtExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Character at index 1: " + str.charAt(1));
    }
}

Output:

Character at index 1: e

3. substring(int beginIndex, int endIndex)

Returns a substring from the specified begin index to the end index.

Example

public class StringSubstringExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Substring (7, 12): " + str.substring(7, 12));
    }
}

Output:

Substring (7, 12): World

4. toLowerCase()

Converts all characters in the string to lowercase.

Example

public class StringToLowerCaseExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Lowercase: " + str.toLowerCase());
    }
}

Output:

Lowercase: hello, world!

5. toUpperCase()

Converts all characters in the string to uppercase.

Example

public class StringToUpperCaseExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Uppercase: " + str.toUpperCase());
    }
}

Output:

Uppercase: HELLO, WORLD!

6. trim()

Removes leading and trailing whitespace.

Example

public class StringTrimExample {
    public static void main(String[] args) {
        String str = "  Hello, World!  ";
        System.out.println("Trimmed: " + str.trim());
    }
}

Output:

Trimmed: Hello, World!

7. replace(char oldChar, char newChar)

Replaces all occurrences of the specified old character with the new character.

Example

public class StringReplaceExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Replaced: " + str.replace('o', '0'));
    }
}

Output:

Replaced: Hell0, W0rld!

8. indexOf()

Returns the index within this string of the first occurrence of the specified character or substring.

Example

public class StringIndexOfExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Index of 'W': " + str.indexOf('W'));
        System.out.println("Index of 'World': " + str.indexOf("World"));
    }
}

Output:

Index of 'W': 7
Index of 'World': 7

9. contains()

Checks if the string contains the specified character sequence.

Example

public class StringContainsExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Contains 'World': " + str.contains("World"));
        System.out.println("Contains 'Java': " + str.contains("Java"));
    }
}

Output:

Contains 'World': true
Contains 'Java': false

10. startsWith()

Checks if the string starts with the specified prefix.

Example

public class StringStartsWithExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Starts with 'Hello': " + str.startsWith("Hello"));
        System.out.println("Starts with 'World': " + str.startsWith("World"));
    }
}

Output:

Starts with 'Hello': true
Starts with 'World': false

11. endsWith()

Checks if the string ends with the specified suffix.

Example

public class StringEndsWithExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        System.out.println("Ends with 'World!': " + str.endsWith("World!"));
        System.out.println("Ends with 'Hello': " + str.endsWith("Hello"));
    }
}

Output:

Ends with 'World!': true
Ends with 'Hello': false

12. split()

Splits the string into an array of substrings based on the specified delimiter.

Example

public class StringSplitExample {
    public static void main(String[] args) {
        String str = "Hello, World! Welcome to Java.";
        String[] words = str.split(" ");
        for (String word : words) {
            System.out.println(word);
        }
    }
}

Output:

Hello,
World!
Welcome
to
Java.

13. concat()

Concatenates the specified string to the end of the current string.

Example

public class StringConcatExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = " World";
        System.out.println("Concatenated String: " + str1.concat(str2));
    }
}

Output:

Concatenated String: Hello World

Key Takeaways

  • Java String methods provide a powerful way to manipulate and handle strings.
  • Methods like length(), charAt(), substring(), toLowerCase(), toUpperCase(), trim(), replace(), indexOf(), contains(), startsWith(), endsWith(), split(), and concat() are commonly used for various string operations.
  • Understanding and using these methods effectively can enhance your Java programming skills.
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