Java字符串comparsion [英] Java string comparsion

问题描述

我想实现一个简单的密码塞萨尔。我在与codeS基于一个新的关键[]字符串函数的麻烦。在这里我表示，我怎么设置我的钥匙。

I'm trying to implement a simple cesar cipher. I'm having trouble with the function that codes a string based on a new key[]. Here I shown, how I setup my key.

private String[] alphabet =  {"a", "b", "c","d", "e", "f","g", "h", "i","j", "k", "l","m", "n", "o",
            "p", "q", "r","s", "t", "u","v", "w", "x","u", "z"};

public String[] CoderNewKey(int shift) {
    _NewKey = null;
    _NewKey = new String[25];

    for (int i = 0; i < 25; i++) {
        _NewKey[i] = alphabet[(i + shift) % 25];
    }
    return _NewKey;
}

我的问题是codeR，没有任何的if语句是永远正确的，rtnstring始终只是。

The problem I have is with Coder, none of the if statements are ever true, and rtnstring is always just "".

public String Coder(String[] key, String msg){
    String rtnstring = "";

    for ( int i = 0; i < msg.length();i++){

        for (int x = 0; x<26 ; x++){
            if ( msg.substring(i, i+1) == alphabet[x]){

                rtnstring.concat(key[x]);
            }if (msg.substring(i, i+1) == " "){

                rtnstring.concat(" ");
            }
        }
    }
    return rtnstring;
}

下面是我为codeR方法的逻辑。

Here is my logic for the coder method.

它经历一次的弦乐味精1个字母。它匹配其字母表中的索引信，然后创建基于该指数在给定的密钥一个新的字符串。

It goes through the String msg 1 letter at a time. It matches the letter with its index in the alphabet, then it creates a new string based on the index's in the given key.

推荐答案

您需要使用的 等于（） 从String类的方法。当您使用 == 你比较两个对象的引用变量（这是不是在你的code相同）

You need to use equals() method from the String class. When you use == you are comparing the reference variable of two objects (which is not same in your code)

  +----------+                        +----------+
  |          |     What you need      |          |
  |  "   " <-------to compare-----------> "a"    |
  |          |                        |          |
  |          |                        |          |
  +----------+                        +----------+
       ^                                   ^
       |                                   |
       +              What you             +
   rtnstring <------+ erroneously +---->  msg
                      compare

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