15.1.3 repeat() Explained

The repeat() method in Java SE 11 is a useful feature for manipulating strings. It allows you to create a new string by repeating the original string a specified number of times. This method is part of the String class and is particularly useful for generating patterns, padding strings, or creating repetitive text efficiently.

Key Concepts

1. String Class

The String class in Java represents a sequence of characters. It provides various methods for manipulating strings, including the repeat() method introduced in Java SE 11.

Example

        String original = "abc";
    

2. repeat() Method

The repeat() method is an instance method of the String class. It takes an integer parameter that specifies the number of times the original string should be repeated. The method returns a new string that is the result of repeating the original string the specified number of times.

Example

        String repeated = original.repeat(3);
        // Output: "abcabcabc"
    

3. Edge Cases

The repeat() method handles edge cases gracefully. If the number of repetitions is zero, the method returns an empty string. If the number of repetitions is negative, the method throws an IllegalArgumentException.

Example

        String empty = original.repeat(0);
        // Output: ""
        
        try {
            String invalid = original.repeat(-1);
        } catch (IllegalArgumentException e) {
            // Exception handling
        }
    

4. Performance Considerations

The repeat() method is optimized for performance. It efficiently handles large numbers of repetitions by leveraging internal string optimizations. This makes it suitable for use in performance-critical applications.

Example

        String largeRepeat = original.repeat(1000000);
        // Efficiently creates a string with 1,000,000 repetitions
    

Examples and Analogies

Think of the repeat() method as a tool for creating patterns or repetitive sequences. For example, if you need to create a string that represents a dashed line, you can use the repeat() method to repeat the dash character a specified number of times.

Example

        String dashLine = "-".repeat(20);
        // Output: "--------------------"
    

Another analogy is using repeat() to create a string that represents a series of stars for a rating system. You can repeat the star character to represent different ratings.

Example

        String rating = "*".repeat(5);
        // Output: "*****"
    

By mastering the repeat() method, you can efficiently manipulate strings in your Java SE 11 applications, making your code more concise and readable.