Java，检查字符串是否为回文。不区分大小写

Java, Check if a String is a palindrome. Case insensitive

提问by user2121604

I want to write a java method to return true if a string is a palindrome.

如果字符串是回文，我想编写一个 java 方法来返回 true。

Here is what I have so far:

这是我到目前为止所拥有的：

String palindrome = "...";
boolean isPalindrome = palindrome.equals(
   new StringBuilder(palindrome).reverse().toString());

My problem with this is that it does not consider a word like: Race carto be a palindrome.

我的问题是它不考虑这样的词：Race car成为回文。

Doc, note, I dissent. A fast never prevents a fatness. I diet on cod.

What is the best way to test if this is a palindrome, with case insensitivity and ignoring punctuation.

测试这是否是回文的最佳方法是什么，不区分大小写并忽略标点符号。

回答by Fr_nkenstien

Use this regex to remove all punctuation and spaces and convert it to lower case

使用此正则表达式删除所有标点符号和空格并将其转换为小写

String palindrome = "..." // from elsewhere
boolean isPalindrome = palindrome.replaceAll("[^A-Za-z]", "").toLowerCase().equals(new StringBuilder(palindrome.replaceAll("[^A-Za-z]", "").toLowerCase()).reverse().toString());

回答by Sudhanshu Umalkar

Try this ..

试试这个 ..

public static void main(String[] args) {

    boolean notPalindrome = false;
    String string = "Doc, note, I dissent. A fast never prevents a fatness. I diet on cod";

    string = string.replaceAll("[^a-zA-Z]+","").toLowerCase();

    char[] array = string.toCharArray();
    for(int i=0, j=array.length-1; i<j; i++, j--) {
        if(array[i] != array[j]) {
            notPalindrome = true;
            break;
        }
    }
    System.out.println(string + " is palindrome? " + !notPalindrome);
}

回答by SudoRahul

Use the below regex, to keep even numericcharacters in the Palindrome, if needed. Else, you can just remove the 0-9from the regex.

numeric如果需要，使用下面的正则表达式在回文中保留偶数字符。否则，您可以0-9从正则表达式中删除。

String palindrome = "..." // from elsewhere
String regex = "[^A-Za-z0-9]";
boolean isPalindrome = palindrome.equals(new StringBuilder(palindrome.replaceAll(regex, "").toLowerCase()).reverse().toString());

回答by Bhushan

Here is a non regexsolution.

这是一个非regex解决方案。

public class so4
{
public static void main(String args[])
{
    String str = "Doc, note, I dissent. A fast never prevents a fatness. I diet on cod";
    char c[] =str.toCharArray();
    String newStr="";
    for(int i=0;i<c.length;i++)
    {
        if( (c[i]>=65 && c[i]<=90) || (c[i]>=97 && c[i]<=122))  //check ASCII values (A-Z 65-90) and (a-z 97-122)
        {
            newStr = newStr + c[i]; 
        }
    }
    boolean isPalindrome = newStr.toLowerCase().equals(new StringBuilder(newStr.toLowerCase()).reverse().toString());
    System.out.println(isPalindrome);
}
}

回答by jahroy

1. convert to lower case

2. use a regex to remove everything but letters

3. reverse the string using a StringBuilder

4. compare the strings for equality

1. 转换为小写

2. 使用正则表达式删除除字母以外的所有内容

3. 使用StringBuilder反转字符串

4. 比较字符串是否相等

Code:

代码：

/**
 *  Returns true if s is a palindrome, ignoring whitespace
 *  punctuation, and capitalization.  Returns false otherwise.  
 */

public boolean isPalindrome(String s) {
    String forward = s.toLowerCase().replaceAll("[^a-z]", "");
    String reverse = new StringBuilder(forward).reverse().toString();
    return forward.equals(reverse);
}

For more info, see the documentation for Stringand StringBuilder:

有关更多信息，请参阅String和StringBuilder的文档：

• String.toLowerCase()
• String.replaceAll()
• StringBuilder.reverse()

• String.toLowerCase()
• String.replaceAll()
• StringBuilder.reverse()

You can also find it by googling "Java 7 String" and clicking the first result.

您也可以通过谷歌搜索“ Java 7 String”并单击第一个结果来找到它。