0

我创建了一个字符串回文程序，但我得到了一个 Nullpointer 异常。

这是我编写的代码：

public class JavaApplication2 {

    /**
     * @param args the command line arguments
     */
    char c[]={'i','c','i','c','i'};
    String s = new String(c);
    String s1=null;
    int i,j;
    char c1[];
    public static void main(String[] args) {
        //TODO code application logichere

        JavaApplication2 ja=new JavaApplication2();
        ja.palindrome();
        ja.ans();
        boolean b1= ja.ans();
        System.out.println(b1);
    }

    public void palindrome()
    {
        for(i=s.length()-1,j=0;i>=0;i--)
        {
            c1[j]=s.charAt(i);
            j++;
        }
    }

    public boolean ans()
    {
        String s2= new String(c1);
        if(s2.equals(s))
        {
            return true;
        }
        else
            return false;

    }
}

我无法弄清楚如何处理它以及发生此错误的确切原因。

4

5 回答 5

0

问题是char c1[];没有被初始化。因此这一行给你一个空指针：

String s2 = new String(c1);

初始化变量：

char c1[] = {};

现在 NullPointer 不见了，但这不是最终版本，你需要用你的逻辑填充它。

于 2013-08-18T16:36:31.347 回答
0

可以做几件事以使此代码正常工作。你可以试试这个。

public class JavaApplication2 {
char c[]={'i','c','i','c','i'};
String s = new String(c);
int i,j;
char c1[]=new char[s.length()] ; // initialize c1
public static void main(String[] args) {
    JavaApplication2 ja=new JavaApplication2();
    ja.palindrome();
    ja.ans();
    boolean b1= ja.ans();
    System.out.println(b1);
}

public void palindrome()
{
    for(i=s.length()-1,j=0;i>=0;i--)
    {
        c1[j]=s.charAt(i);// populate c1
        j++;
    }
}

public boolean ans()
{
    String s2= new String(c1);
    if(s2.equals(s))// check equality of s2 and s
    {
        return true;
    }
    else
        return false;

}
}
于 2013-08-18T16:47:41.137 回答
0

新的 StringBuilder(str1).reverser().toString();

于 2013-08-18T16:50:43.377 回答
0

这是我的代码：

class MyClass

{


public static void main (String[] args)


    {
        Scanner sc=new Scanner(System.in);

            int T=sc.nextInt();


            for(int j=0;j<T;j++){
            String str=sc.next();

            String revstring="";

            for(int i=str.length()-1;i>=0;--i){

            revstring +=str.charAt(i);
            }

            if(revstring.equalsIgnoreCase(str)){
            System.out.println("Yes");
            }
            else{
            System.out.println("No");
            }
        }
    }
}
于 2017-10-03T12:38:18.577 回答
0

只需从最后一个索引遍历到第一个索引，就很容易反转字符或整数数组。

int[] myArray = new int[10];//Array size is 10
//Traverse from last index= 9 to the first Index= 0 
for(int i= myArray.length-1; i>= 0 ; --i){
    System.out.print(myArray[i]);//here i is last index=10-1=9.
}

但是我尝试通过忽略大小写而不忽略大小写来检查用户给定的字符串是回文。

import java.util.Scanner;

public class Palindrome {

    public void StringPalindrome(String original) {
        String reverse = "";
        for (int i = original.length() - 1; i >= 0; i--) {
            reverse += original.charAt(i);
        }
        if (original.equals(reverse)) {
            System.out.println("Entered string is palindrome \n" + "Original = " + original + "\n Reverse = " + reverse);
        } else {
            System.out.println("Entered string is not a palindrome.");
        }
    }

    public void StringPalindromeIgnoreCase(String original) {
        String reverse = "";
        for (int i = original.length() - 1; i >= 0; i--) {
            reverse += original.charAt(i);
        }
        if (original.equalsIgnoreCase(reverse)) {
            System.out.println("Entered string is palindrome \n" + "Original = " + original + "\n Reverse = " + reverse);
        } else {
            System.out.println("Entered string is not a palindrome.");
        }
    }

    public void reverseArrayInteger(int number[]) {
        for (int i = number.length - 1; i >= 0; i--) {
            System.out.print(number[i]);
        }
        System.out.println(" ");
    }

    public static void main(String[] args) {
        Palindrome myPalindrom = new Palindrome();
        testReverseIntegerArray(myPalindrom);
        testStringPalindrome(myPalindrom);
        testStringPaligrameIgnoreCase(myPalindrom);
    }

    public static void testReverseIntegerArray(Palindrome myPalindrom) {
        int[] number = {1, 3, 5, 7, 8};
        myPalindrom.reverseArrayInteger(number);
    }

    public static void testStringPalindrome(Palindrome myPalindrom) {
        Scanner in = new Scanner(System.in);
        String original;
        System.out.println("Enter a string to check if it is a palindrome");
        original = in.nextLine();
        myPalindrom.StringPalindrome(original);
    }

    public static void testStringPaligrameIgnoreCase(Palindrome myPalindrom) {
        Scanner in = new Scanner(System.in);
        String original;
        System.out.println("Enter a string to check if it is a palindrome");
        original = in.nextLine();
        myPalindrom.StringPalindromeIgnoreCase(original);
    }
}

简单输出：

87531 
Enter a string to check if it is a palindrome
MADAM
Entered string is palindrome 
Original = MADAM
 Reverse = MADAM
Enter a string to check if it is a palindrome
MaDAm
Entered string is palindrome 
Original = MaDAm
Reverse = mADaM
于 2016-11-24T13:22:51.917 回答