Reversing a String in Java: Methods and Examples

回答：

Reversing a string in Java can be accomplished in several ways. Below, I'll introduce a few common methods to reverse a string, along with examples for each method.

Method 1: Using `StringBuilder`

The StringBuilder class in Java has a built-in method called reverse() that can be used to reverse a string easily.

public class ReverseStringExample {
    public static void main(String[] args) {
        String original = "Hello, World!";
        String reversed = new StringBuilder(original).reverse().toString();
        System.out.println("Original: " + original);
        System.out.println("Reversed: " + reversed);
    }
}

Method 2: Using a Loop

You can also reverse a string manually by using a loop to build the reversed string character by character.

public class ReverseStringExample {
    public static void main(String[] args) {
        String original = "Hello, World!";
        String reversed = "";

        for (int i = original.length() - 1; i >= 0; i--) {
            reversed += original.charAt(i);
        }

        System.out.println("Original: " + original);
        System.out.println("Reversed: " + reversed);
    }
}

Method 3: Using Recursion

Another approach is to use recursion to reverse a string. This method is less common but demonstrates the concept of recursion.

public class ReverseStringExample {
    public static void main(String[] args) {
        String original = "Hello, World!";
        String reversed = reverseString(original);
        System.out.println("Original: " + original);
        System.out.println("Reversed: " + reversed);
    }

    public static String reverseString(String str) {
        if (str.isEmpty()) {
            return str;
        }
        return reverseString(str.substring(1)) + str.charAt(0);
    }
}

Method 4: Using Character Array

You can also convert the string to a character array, reverse the array, and then create a new string from the reversed array.

public class ReverseStringExample {
    public static void main(String[] args) {
        String original = "Hello, World!";
        char[] charArray = original.toCharArray();
        String reversed = "";

        for (int i = charArray.length - 1; i >= 0; i--) {
            reversed += charArray[i];
        }

        System.out.println("Original: " + original);
        System.out.println("Reversed: " + reversed);
    }
}

Summary

These are some of the common methods to reverse a string in Java. Each method has its own advantages and use cases:

StringBuilder: Simple and efficient for most cases.
Loop: Good for understanding the mechanics of string manipulation.
Recursion: A more advanced technique that showcases recursive thinking.
Character Array: Useful for understanding how strings are represented in memory.

You can choose any of these methods based on your specific needs and preferences!