变量未初始化 - 虽然我是谁？ [英] Variable not Initialized - Although I am?

问题描述

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    情况下0：
        
        
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    情况1：
        
        
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    案例2：
        
        
    默认：
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Answered

Mike Suggested I added some code to the

default: 
break;

part of the switch, I added an exception to it, and no need to change anything else. Code now runs successfully. Thanks guys!

EDITED FOR READABILITY:

Error: "Description Resource Path Location Type The local variable messages may not have been initialized TweetFragment.java /Offline Twitter/src/com/deadpixels/offline/twitter line 78 Java Problem"

for line:

int handleStartsAt = messages[i].indexOf('@');

And the same error happens twice on line 80, that being:

ph = messages[i].substring(handleStartsAt, messages[i].length()); 

As far as your questions, the

default: 
break;

line was added as the int tweet type should only be either 0, 1, or 2. The function is called within a controlled environment and that way I am sure the call will not return an exception.

END OF EDIT.

I have quick question. I am trying to create a method to return a String array, this String array has a size that will change depending on the message type that is passed to the method as a parameter. I am having some issues getting this done, as apparently I am not initializing my variable; although, I think I am.

The variable I am having issues with is the "messages" array.

Bear in mind that I cannot declare the following:

String [] messages = new String [arrayLength];

As at this point in the call I do not know the length of the array. And I cannot do this:

String [] messages = null;

since after this, I will run into a runtime error, despite of not getting alerts at compile time.

Also, just to clarify, I would have though that:

messages = OfflineTwitter.mentions;

the above line would be initializing the variable, "OfflineTwitter.mentions" is an array, only stored in a different class.

Here is the code snippet.

public String[] getHandles (int tweetType) {

    int arrayLength = 0;
    String [] handles;
    String [] messages;

    switch (tweetType) {
    case 0:
        arrayLength = OfflineTwitter.mentions.length;
        messages = OfflineTwitter.mentions;
        break;
    case 1: 
        arrayLength = OfflineTwitter.directMessages.length;
        messages = OfflineTwitter.directMessages;
        break;
    case 2:
        arrayLength = OfflineTwitter.allTweets.length;
        messages = OfflineTwitter.allTweets;
    default:
        break;
    }

    handles = new String [arrayLength]; 

    for (int i = 0; i < arrayLength; i++) {
        int handleStartsAt = messages[i].indexOf('@');
        String ph = "";
        ph = messages[i].substring(handleStartsAt, messages[i].length());
        int handleEndsAt = ph.indexOf(":");
        String sender = ph.substring(0, handleEndsAt);
        handles[i] = sender;  
    }       

    return handles;
}

解决方案

If tweetType < 0 || tweetType > 2 then

default:
    break;

is reached which does not assign a value to messages.

You need to assign a value in the default branch, or throw an exception, or return so that the array is initialized at first use.

Perhaps change that to

default:
    throw new IllegalArgumentException("Invalid tweet type : " + tweetType);

or ideally change tweetType to be an enum so that you can cover all cases exhaustively.

enum TweetType {
  MENTIONS,
  DIRECT_MESSAGES,
  ALL_MESSAGES,
  ;
}

and change int tweetType to TweetType tweetType.

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