局部变量未使用 [英] Local variable not used

问题描述

我试图测试一个输入的单词是否是回文（相同的拼写正向和反向）。从我可以看到它应该工作，但Eclipse说局部变量isPalindrome的值不被使用，但它被使用。问题是，即使这个词不是一个回文，它说是这样的。

  import java.util.Scanner; 
 
 public class Palindrome {
 public static void main（String [] args）{
 String phrase; 
 char [] phraseLetters; 
 int endChar; 
 boolean isPalindrome; 
 
扫描仪输入=新的扫描仪（System.in）; 
 System.out.println（输入单词或短语）; 
 phrase = input.nextLine（）; 
 input.close（）; 
 
 phrase = phrase.toLowerCase（）; 
 phrase = phrase.replaceAll（，）; 
 phraseLetters = phrase.toCharArray（）; 
 
 endChar = phraseLetters.length  -  1; （int i = 0; i< phraseLetters.length; i ++）{
 if（phraseLetters [i]！= phraseLetters [endChar]）{
 isPalindrome = false ; 
} else {
 isPalindrome = true; 
 endChar  -  = 1; 
} 
} 
 
 if（isPalindrome = true）{
 System.out.println（输入的这个单词或短语是一个回文）​​; 
} else {
 System.out.println（这个词或短语不是回文）; 
} 
} 
} 
  

编辑：我尝试过if（isPalindrome == true）

和

  if（isPalindrome）
  

在这两种情况下，Eclipse说本地变量isPalindrome可能未被初始化，在此if条件中。

FINAL EDIT：

我已经移动了，并重写了这段代码，但是如果还有人仍然修改了我的原始代码看看这个。

我在代码开头初始化了isPalindrome：

Boolean isPalinddrome = True;

我将for循环条件更改为：

for（int i = 0;（i< phraseLetters.length）&&（isPalindrome）; i ++）

$ b $如果（isPalindrome = true）到 if（isPalindrome）

<如果（isPalindrome = true）应该是 if（isPalindrome == true），则div class =h2_lin>解决方案

（或 if（isPalindrome） 更好！实际上这个错误是另一个很好的理由，为什么不问，如果 someBoolean == true 这是一个坏的风格）

By键入 if（isPalindrome = true）您再次将值 true 分配给变量 isPalindrome 。而且由于你只是为它赋值，所以编译器会向你发出关于未使用的变量的警告。

这也是很好的： p>

在运行时，赋值表达式的结果是分配发生后变量
的值。
赋值表达式的结果本身不是一个变量。

所以，当你执行 if（isPalindrome = true）然后if条件总是满足

I am trying to make a test of whether an inputted word is a palindrome or not (the same spelled forward and backward). From what I can see it should work but Eclipse says "The value of the local variable isPalindrome is not used" , but it is used. The problem is that even if the word is not a palindrome it says it is.

import java.util.Scanner;

public class Palindrome {
    public static void main(String[] args) {
        String phrase;
        char[] phraseLetters;
        int endChar;
        boolean isPalindrome;

        Scanner input = new Scanner(System.in);
        System.out.println("Enter a word or phrase.");
        phrase = input.nextLine();
        input.close();

        phrase = phrase.toLowerCase();
        phrase = phrase.replaceAll(" ","");
        phraseLetters = phrase.toCharArray();

        endChar = phraseLetters.length - 1;

        for (int i = 0; i < phraseLetters.length; i++) {
            if (phraseLetters[i] != phraseLetters[endChar]) {
                isPalindrome = false;   
            } else {
                isPalindrome = true;
                endChar -= 1;
            }
        }

        if (isPalindrome = true) {
            System.out.println("This word or phrase entered is a palindrome.");
        } else {
            System.out.println("This word or phrase is not a palindrome.");
        }
    }
}

EDIT: I have tried the if statement being

    if (isPalindrome == true) 

and

    if (isPalindrome)

In both cases Eclipse says "The local variable isPalindrome may not have been initialized," in this if condition.

FINAL EDIT:

I have since moved on, and rewritten this code, however I just went back and fixed my original code if anyone still looks at this.

I initialized isPalindrome at the beginning of the code:

Boolean isPalinddrome = True;

I changed the for-loop condition to:

for (int i = 0; (i < phraseLetters.length) && (isPalindrome); i++)

Finally I changed if (isPalindrome = true) to if (isPalindrome)

解决方案

if (isPalindrome = true) should be if (isPalindrome == true) (or if (isPalindrome) better! Actually this error is another good reason why not asking if someBoolean == true which is a bad style)

By typing if (isPalindrome = true) you're assigning, again, the value true to the variable isPalindrome. And since you're only assigning value to it, the compiler warns you about unused variable.

It's also good to know this:

At run time, the result of the assignment expression is the value of the variable after the assignment has occurred. The result of an assignment expression is not itself a variable.

So, when you do if (isPalindrome = true) then the if condition is always satisfied.

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