在Java中反转字符串

本文通过示例讨论了在Java中反转字符串的不同方法。
例子：

先决条件： Java中的String vs StringBuilder vs StringBuffer
以下是关于 String 和 StringBuilder 类的一些有趣事实：
1. String 的对象是不可变的。
2. Java中的String类没有reverse()方法，但是StringBuilder类内置了reverse()方法。
3. StringBuilder类没有toCharArray()方法，而String类有toCharArray()方法。

1. The idea is to traverse the length of the string 
2. Extract each character while traversing 
3. Add each character in front of the existing string

Java

// java program to reverse a word
 
import java.io.*;
import java.util.Scanner;
 
class GFG {
    public static void main (String[] args) {
       
        String str= "Geeks", nstr="";
        char ch;
       
      System.out.print("Original word: ");
      System.out.println("Geeks"); //Example word
       
      for (int i=0; i

---

• 将字符串转换为字节： getBytes() 方法用于将输入字符串转换为字节[]。
方法：


1. Create a temporary byte[]  of length equal 
   to the length of the input string.
2. Store the bytes (which we get by using 
   getBytes() method) in reverse order into 
   the temporary byte[] .
3. Create a new String abject using byte[] to
   store result.

Java

// Java program to ReverseString using ByteArray.
import java.lang.*;
import java.io.*;
import java.util.*;
 
// Class of ReverseString
class ReverseString {
    public static void main(String[] args)
    {
        String input = "GeeksforGeeks";
 
        // getBytes() method to convert string
        // into bytes[].
        byte[] strAsByteArray = input.getBytes();
 
        byte[] result = new byte[strAsByteArray.length];
 
        // Store result in reverse order into the
        // result byte[]
        for (int i = 0; i < strAsByteArray.length; i++)
            result[i] = strAsByteArray[strAsByteArray.length - i - 1];
 
        System.out.println(new String(result));
    }
}

输出：

skeeGrofskeeG

• 使用StringBuilder类的内置reverse()方法： String类没有reverse()方法，我们需要将输入的字符串转换为StringBuilder，这是通过StringBuilder的append方法实现的。之后，通过从第一个索引到最后一个索引进行扫描，打印出反转字符串的字符。

Java

// Java program to ReverseString using StringBuilder
import java.lang.*;
import java.io.*;
import java.util.*;
 
// Class of ReverseString
class ReverseString {
    public static void main(String[] args)
    {
        String input = "Geeks for Geeks";
 
        StringBuilder input1 = new StringBuilder();
 
        // append a string into StringBuilder input1
        input1.append(input);
 
        // reverse StringBuilder input1
        input1.reverse();
 
        // print reversed String
        System.out.println(input1);
    }
}

输出：

skeeG rof skeeG

• 将字符串转换为字符数组：用户输入要反转的字符串。
方法：

1. First, convert String to character array
   by using the built in Java String class 
   method toCharArray().
2. Then, scan the string from end  to start, 
   and print the character one by one.

Java

// Java program to Reverse a String  by
// converting string to characters  one
// by one
import java.lang.*;
import java.io.*;
import java.util.*;
 
// Class of ReverseString
class ReverseString {
    public static void main(String[] args)
    {
        String input = "GeeksForGeeks";
 
        // convert String to character array
        // by using toCharArray
        char[] try1 = input.toCharArray();
 
        for (int i = try1.length - 1; i >= 0; i--)
            System.out.print(try1[i]);
    }
}

输出：

skeeGrofskeeG

• 使用 toCharArray ( )将输入字符串转换为字符数组： 使用 String 类的内置方法 toCharArray() 将输入字符串转换为字符数组。然后，同时从两侧扫描字符数组，即从起始索引（左）和最后一个索引（右）。

1. Set the left index equal to 0 and right 
   index equal to the length of the string -1.
2. Swap the characters of the start index 
   scanning with the last index scanning 
   one by one. After that, increase the left 
   index by 1 (left++) and decrease the right 
   by 1 i.e., (right--) to move on to the next 
   characters in the character array .
3. Continue till left is less than or equal to
   the right.

Java

// Java program to Reverse a String using swapping
// of variables
import java.lang.*;
import java.io.*;
import java.util.*;
 
// Class of ReverseString
class ReverseString {
    public static void main(String[] args)
    {
        String input = "Geeks For Geeks";
        char[] temparray = input.toCharArray();
        int left, right = 0;
        right = temparray.length - 1;
 
        for (left = 0; left < right; left++, right--) {
            // Swap values of left and right
            char temp = temparray[left];
            temparray[left] = temparray[right];
            temparray[right] = temp;
        }
 
        for (char c : temparray)
            System.out.print(c);
        System.out.println();
    }
}

输出：

skeeG roF skeeG

• 使用 ArrayList 对象：使用内置的 toCharArray() 方法将输入字符串转换为字符数组。然后，将数组的字符添加到 ArrayList 对象中。 Java还为 Collections 类内置了 reverse() 方法。由于 Collections 类的 reverse() 方法需要一个列表对象，为了反转列表，我们将传递 ArrayList 对象，它是一种字符列表。

1. We copy String contents to an object 
   of ArrayList.
1. We create a ListIterator object by using 
   the listIterator() method on the ArrayList 
   object.
2. ListIterator object is used to iterate over 
   the list.
3. ListIterator object helps us to iterate 
   over the reversed list and print it one 
   by one to the output screen.

Java

// Java program to Reverse a String using ListIterator
import java.lang.*;
import java.io.*;
import java.util.*;
 
// Class of ReverseString
class ReverseString {
    public static void main(String[] args)
    {
        String input = "Geeks For Geeks";
        char[] hello = input.toCharArray();
        List trial1 = new ArrayList<>();
 
        for (char c : hello)
            trial1.add(c);
 
        Collections.reverse(trial1);
        ListIterator li = trial1.listIterator();
        while (li.hasNext())
            System.out.print(li.next());
    }
}

输出：

skeeG roF skeeG

• 使用StringBuffer： String类没有reverse()方法，我们需要将输入字符串转换为StringBuffer，这是通过使用StringBuffer的reverse方法来实现的。

Java

// Java program to demonstrate conversion from
// String to StringBuffer and reverse of string
import java.lang.*;
import java.io.*;
import java.util.*;
 
public class Test {
    public static void main(String[] args)
    {
        String str = "Geeks";
 
        // conversion from String object to StringBuffer
        StringBuffer sbr = new StringBuffer(str);
        // To reverse the string
        sbr.reverse();
        System.out.println(sbr);
    }
}

输出：

skeeG