Java StringBuilder repeat() Method

The StringBuilder.repeat() method was introduced in Java 21 and is used to repeat a specified character or CharSequence multiple times within a StringBuilder object.

Table of Contents

1. Introduction
2. repeat Method Syntax
3. Examples
   • Repeating a Code Point
   • Repeating a CharSequence
4. Real-World Use Case
5. Conclusion

Introduction

The StringBuilder.repeat() method allows you to repeat a specified character (represented as a Unicode code point) or a CharSequence multiple times and append the result to the StringBuilder object. This is useful for generating repeated patterns, such as padding strings or creating repeated sequences of characters.

repeat() Method Syntax

The StringBuilder class provides two overloaded repeat methods:

1. repeat(int codePoint, int count)
2. repeat(CharSequence cs, int count)

Method 1: repeat(int codePoint, int count)

The syntax for repeating a code point is as follows:

public StringBuilder repeat(int codePoint, int count)

• codePoint: The Unicode code point of the character to be repeated.
• count: The number of times to repeat the character.

Method 2: repeat(CharSequence cs, int count)

The syntax for repeating a CharSequence is as follows:

public StringBuilder repeat(CharSequence cs, int count)

• cs: The CharSequence to be repeated.
• count: The number of times to repeat the CharSequence.

Examples

Repeating a Code Point

The repeat(int codePoint, int count) method can be used to repeat a character represented by its Unicode code point multiple times.

Example

public class StringBuilderRepeatExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();

        // Repeat the character 'A' (Unicode code point 65) 5 times
        sb.repeat(65, 5);

        // Print the result
        System.out.println("StringBuilder after repeating code point: " + sb.toString());
    }
}

Output:

StringBuilder after repeating code point: AAAAA

Repeating a CharSequence

The repeat(CharSequence cs, int count) method can be used to repeat a CharSequence multiple times.

Example

public class StringBuilderRepeatExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();

        // Repeat the CharSequence "Java" 3 times
        sb.repeat("Java", 3);

        // Print the result
        System.out.println("StringBuilder after repeating CharSequence: " + sb.toString());
    }
}

Output:

StringBuilder after repeating CharSequence: JavaJavaJava

Real-World Use Case

Example: Creating a Repeated Pattern for Formatting

In a real-world scenario, you might need to create a repeated pattern for formatting purposes, such as generating a separator line in a text file or console output.

Example Code

public class PatternGenerator {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();

        // Generate a repeated pattern of 50 dashes
        sb.repeat('-', 50);

        // Print the repeated pattern
        System.out.println(sb.toString());
    }
}

Output:

--------------------------------------------------

Example: Padding a String

Another use case could be padding a string with repeated characters to ensure it meets a certain length.

Example Code

public class StringPadding {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Data");

        // Calculate how many spaces are needed to pad to 10 characters
        int paddingCount = 10 - sb.length();

        // Append the spaces to the StringBuilder
        sb.repeat(' ', paddingCount);

        // Print the padded string
        System.out.println("Padded string: '" + sb.toString() + "'");
    }
}

Output:

Padded string: 'Data      '

Conclusion

The StringBuilder.repeat() method introduced in Java 21 is used for repeating characters or CharSequence multiple times within a StringBuilder object. By understanding how to use these overloaded methods, you can efficiently generate repeated patterns and handle various scenarios where duplicating a sequence of characters is required. Whether you need to repeat a single character, a string, or create padding for formatting purposes, the repeat method provides a versatile solution for these tasks.