在Java中反转一个字符串

Question

我"Hello World"保留了一个名为的String变量hi.

我需要打印它,但反过来.

我怎样才能做到这一点？我知道Java中已经内置了某种功能.

相关:用Java反转"Hello World"字符串的每个单词

Answer 1

你可以用这个:

new StringBuilder(hi).reverse().toString()

或者,对于早于JDK 1.5的版本,使用java.util.StringBuffer而不是StringBuilder- 它们具有相同的API.感谢评论员指出,StringBuilder如果没有并发问题,现在首选.

Answer 2

对于在线法官的问题,不允许StringBuilder或者StringBuffer,你可以做到这一点的地方使用char[]如下:

public static String reverse(String input){
    char[] in = input.toCharArray();
    int begin=0;
    int end=in.length-1;
    char temp;
    while(end>begin){
        temp = in[begin];
        in[begin]=in[end];
        in[end] = temp;
        end--;
        begin++;
    }
    return new String(in);
}

Answer 3

public static String reverseIt(String source) {
    int i, len = source.length();
    StringBuilder dest = new StringBuilder(len);

    for (i = (len - 1); i >= 0; i--){
        dest.append(source.charAt(i));
    }

    return dest.toString();
}

http://www.java2s.com/Code/Java/Language-Basics/ReverseStringTest.htm

Answer 4

String string="whatever";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println(reverse);

Answer 5

我这样做是通过以下两种方式实现的:

通过CHARACTERS反转字符串:

public static void main(String[] args) {
    // Using traditional approach
    String result="";
    for(int i=string.length()-1; i>=0; i--) {
        result = result + string.charAt(i);
    }
    System.out.println(result);

    // Using StringBuffer class
    StringBuffer buffer = new StringBuffer(string);
    System.out.println(buffer.reverse());    
}

由WORDS反向字符串:

public static void reverseStringByWords(String string) {
    StringBuilder stringBuilder = new StringBuilder();
    String[] words = string.split(" ");

    for (int j = words.length-1; j >= 0; j--) {
        stringBuilder.append(words[j]).append(' ');
    }
    System.out.println("Reverse words: " + stringBuilder);
}

Answer 6

看一下StringBuffer下的Java 6 API

String s = "sample";
String result = new StringBuffer(s).reverse().toString();

Answer 7

以下是使用递归的示例:

public void reverseString() {
    String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    String reverseAlphabet = reverse(alphabet, alphabet.length()-1);
}

String reverse(String stringToReverse, int index){
    if(index == 0){
        return stringToReverse.charAt(0) + "";
    }

    char letter = stringToReverse.charAt(index);
    return letter + reverse(stringToReverse, index-1);
}

Answer 8

这是一个低级解决方案:

import java.util.Scanner;

public class class1 {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String inpStr = in.nextLine();
        System.out.println("Original String :" + inpStr);
        char temp;
        char[] arr = inpStr.toCharArray();
        int len = arr.length;
        for(int i=0; i<(inpStr.length())/2; i++,len--){
            temp = arr[i];
            arr[i] = arr[len-1];
            arr[len-1] = temp;
        }

        System.out.println("Reverse String :" + String.valueOf(arr));
    }
}

Answer 9

我尝试使用Stack,只是为了好玩.这是我的代码:

public String reverseString(String s) {
    Stack<Character> stack = new Stack<>();
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < s.length(); i++) {
        stack.push(s.charAt(i));
    }
    while (!stack.empty()) {
        sb.append(stack.pop());
    }
    return sb.toString();

}

Answer 10

使用charAt()方法

String name = "gaurav";
String reversedString = "";
    
for(int i = name.length() - 1; i >= 0; i--){
    reversedString += name.charAt(i);
}

System.out.println(reversedString);

使用toCharArray()方法

String name = "gaurav";
char [] stringCharArray = name.toCharArray();
String reversedString = "";
    
for(int i = stringCharArray.length - 1; i >= 0; i--) {
    reversedString += stringCharArray[i];
}

System.out.println(reversedString);

StringBuilder的使用reverse()方法

String name = "gaurav";
    
String reversedString = new StringBuilder(name).reverse().toString();
    
System.out.println(reversedString);

检查https://coderolls.com/reverse-a-string-in-java/

Answer 11

由于未列出以下方法(使用XOR)来反转字符串,因此我附加此方法以反转字符串.

该算法是基于:

1.(XOR B)XOR B = A.

2.(XOR B)XOR A = B.

代码段:

public class ReverseUsingXOR {
    public static void main(String[] args) {
        String str = "prateek";
        reverseUsingXOR(str.toCharArray());
    }   

    /*Example:
     * str= prateek;
     * str[low]=p;
     * str[high]=k;
     * str[low]=p^k;
     * str[high]=(p^k)^k =p;
     * str[low]=(p^k)^p=k;
     * 
     * */
    public static void reverseUsingXOR(char[] str) {
        int low = 0;
        int high = str.length - 1;

        while (low < high) {
            str[low] = (char) (str[low] ^ str[high]);
            str[high] = (char) (str[low] ^ str[high]);   
            str[low] = (char) (str[low] ^ str[high]);
            low++;
            high--;
        }

        //display reversed string
        for (int i = 0; i < str.length; i++) {
            System.out.print(str[i]);
        }
    }

}

输出:

keetarp

Answer 12

正如其他人指出的那样,首选方法是使用:

new StringBuilder(hi).reverse().toString()

但如果你想自己实现这个,我担心其余的反应都有缺陷.

原因是String表示Unicode点的列表,char[]根据可变长度编码在数组中编码:UTF-16.

这意味着一些代码点使用数组的单个元素(一个代码单元),但其他代码使用其中两个,因此可能有一对字符必须被视为一个单元(连续的"高"和"低"代理)

public static String reverseString(String s) {
    char[] chars = new char[s.length()];
    boolean twoCharCodepoint = false;
    for (int i = 0; i < s.length(); i++) {
        chars[s.length() - 1 - i] = s.charAt(i);
        if (twoCharCodepoint) {
            swap(chars, s.length() - 1 - i, s.length() - i);
        }
        twoCharCodepoint = !Character.isBmpCodePoint(s.codePointAt(i));
    }
    return new String(chars);
}

private static void swap(char[] array, int i, int j) {
    char temp = array[i];
    array[i] = array[j];
    array[j] = temp;
}

public static void main(String[] args) throws Exception {
    FileOutputStream fos = new FileOutputStream("C:/temp/reverse-string.txt");
    StringBuilder sb = new StringBuilder("Linear B Syllable B008 A: ");
    sb.appendCodePoint(65536); //http://unicode-table.com/es/#10000
    sb.append(".");
    fos.write(sb.toString().getBytes("UTF-16"));
    fos.write("\n".getBytes("UTF-16"));
    fos.write(reverseString(sb.toString()).getBytes("UTF-16"));
}

Answer 13

最少的行代码非常简单

public class ReverseString {
    public static void main(String[] args) {
        String s1 = "neelendra";
        for(int i=s1.length()-1;i>=0;i--)
            {
                System.out.print(s1.charAt(i));
            }
    }
}