在Java中如何检查数字/字符串是否是回文？

已发表: 2021-04-13
在Java中如何检查数字：字符串是否为回文？

什么是回文数？

回文数是一个数字（例如 24842），当其数字反转时remains the same 。

以下是其他几个名称：

  • 数字回文
  • 数字回文

在本教程中，我们将介绍如何检查数字和字符串是否为回文的步骤。

如果您有以下任何问题，那么您来对地方了：

  • Java程序检查一个数字是否是回文
  • 回文数的定义
  • 检查给定字符串是否为回文的 Java 程序

步骤——让我们开始吧。

  • 编写程序 CrunchifyFindPalindromeNumber.java
  • 我们将创建 3 个方法：
    • crunchifyFindPalindromeUsingForLoop()
    • crunchifyFindPalindromeUsingWhileLoop()
    • crunchifyFindPalindromeForString()
  • 打印结果

CrunchifyFindPalindromeNumber.java

我们将在这个 Java 程序中使用 AtomicInteger。 它是一个可以自动更新的 int 值。 有关原子访问属性的描述，请参阅 VarHandle 规范。

AtomicInteger 用于原子递增计数器等应用程序中，不能用作 Integer 的替代品。 但是，此类确实扩展了 Number 以允许处理基于数字的类的工具和实用程序进行统一访问。

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package crunchify . com . java . tutorials ;
 
import java . util . concurrent . atomic . AtomicInteger ;
 
/**
* @author Crunchify.com
* In Java How to Check if Number/String is Palindrome or not?
*/
 
public class CrunchifyFindPalindromeNumber {
 
     public static void main ( String [ ] args ) {
 
         crunchifyFindPalindromeUsingForLoop ( 24642 ) ;
         crunchifyFindPalindromeUsingWhileLoop ( 34567 ) ;
 
         crunchifyFindPalindromeUsingForLoop ( 987656789 ) ;
         crunchifyFindPalindromeUsingWhileLoop ( 555555 ) ;
 
         crunchifyFindPalindromeUsingForLoop ( 1 ) ;
         crunchifyFindPalindromeUsingWhileLoop ( 989 ) ;
 
         crunchifyPrint ( "" ) ;
         crunchifyFindPalindromeForString ( "abcdefedcba" ) ;
         crunchifyFindPalindromeForString ( "abcdefghij" ) ;
     }
 
     // Method 1: Find Palindrome for String
     private static void crunchifyFindPalindromeForString ( String crunchifyString ) {
 
         // reverse(): AbstractStringBuilder Causes this character sequence to be replaced by the reverse of the sequence.
         // If there are any surrogate pairs included in the sequence, these are treated as single characters for the reverse operation.
         // Thus, the order of the high-low surrogates is never reversed. Let n be the character length of this character sequence
         // (not the length in char values) just prior to execution of the reverse method. Then the character at index k in the new character
         // sequence is equal to the character at index n-k-1 in the old character sequence.
         String crunchifyReverse = new StringBuffer ( crunchifyString ) . reverse ( ) . toString ( ) ;
 
         // checks whether the string is palindrome or not
         if ( crunchifyString . equals ( crunchifyReverse ) )
             crunchifyPrint ( crunchifyString + " --> Yes, it is a palindrome String." ) ;
         else
             crunchifyPrint ( crunchifyString + " --> No, it is not a palindrome String." ) ;
     }
 
     // Simple Print Utility
     private static void crunchifyPrint ( String crunchifyString ) {
         System . out . println ( crunchifyString ) ;
     }
 
 
     // Method 2: Find Palindrome for Integer using For Loop
     private static void crunchifyFindPalindromeUsingForLoop ( int number ) {
 
         // AtomicInteger: An int value that may be updated atomically.
         // See the VarHandle specification for descriptions of the properties of atomic accesses.
         // An AtomicInteger is used in applications such as atomically incremented counters, and cannot be used as a replacement for an Integer.
         // However, this class does extend Number to allow uniform access by tools and utilities that deal with numerically-based classes.
         AtomicInteger reverseNumber = new AtomicInteger ( ) ;
         AtomicInteger crunchifyRemainder = new AtomicInteger ( ) ;
         int crunchifyOriginal ;
 
         AtomicInteger crunchifyNumber = new AtomicInteger ( number ) ;
         crunchifyOriginal = crunchifyNumber . get ( ) ;
 
         // reversed integer is stored in variable
 
         // updateAndGet Atomically updates (with memory effects as specified by VarHandle.compareAndSet) the current value with the results of
         // applying the given function, returning the updated value.
         // The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads.
         for ( ; crunchifyNumber . get ( ) ! = 0 ; crunchifyNumber . updateAndGet ( v - > v / 10 ) ) {
             crunchifyRemainder . set ( crunchifyNumber . get ( ) % 10 ) ;
             reverseNumber . set ( reverseNumber . get ( ) * 10 + crunchifyRemainder . get ( ) ) ;
         }
 
         // Palindrome is a number that remains the same when its digits are reversed.
         if ( crunchifyOriginal == reverseNumber . get ( ) )
             crunchifyPrint ( crunchifyOriginal + " --> Yes, it is a palindrome Number." ) ;
         else
             crunchifyPrint ( crunchifyOriginal + " --> No, it is not a palindrome Number." ) ;
     }
 
     // Method 3: Find Palindrome for Integer using While Loop
     private static void crunchifyFindPalindromeUsingWhileLoop ( int number ) {
         AtomicInteger reverseNumber = new AtomicInteger ( ) ;
         AtomicInteger crunchifyRemainder = new AtomicInteger ( ) ;
         int crunchifyOriginal ;
 
         int crunchifyNumber = number ;
         crunchifyOriginal = crunchifyNumber ;
 
         while ( crunchifyNumber ! = 0 ) {
             crunchifyRemainder . set ( crunchifyNumber % 10 ) ;
 
             // set() Sets the value to newValue, with memory effects as specified by VarHandle.
             // get() Returns the current value, with memory effects as specified by VarHandle.getVolatile.
             reverseNumber . set ( reverseNumber . get ( ) * 10 + crunchifyRemainder . get ( ) ) ;
             crunchifyNumber /= 10 ;
         }
 
         // Palindrome is a number that remains the same when its digits are reversed.
         if ( crunchifyOriginal == reverseNumber . get ( ) )
             crunchifyPrint ( crunchifyOriginal + " --> Yes, is a palindrome Number." ) ;
         else
             crunchifyPrint ( crunchifyOriginal + " --> No, is not a palindrome Number." ) ;
     }
 
}
 

只需将上面的程序作为 Java 应用程序运行，您应该得到如下结果。

Eclipse / IntelliJ IDEA 控制台结果。

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24642 -- > Yes , it is a palindrome Number .
34567 -- > No , is not a palindrome Number .
987656789 -- > Yes , it is a palindrome Number .
555555 -- > Yes , is a palindrome Number .
1 -- > Yes , it is a palindrome Number .
989 -- > Yes , is a palindrome Number .
 
abcdefedcba -- > Yes , it is a palindrome String .
abcdefghij -- > No , it is not a palindrome String .
 
Process finished with exit code 0

如果您在运行上述程序时遇到任何问题，请告诉我。