内存不足错误：StringBuilder.append 抛出 OutOfMemoryError

Question

I'm working on an application that fetches data from a bluetooth device. But sometimes it throws OOM error while performing some operation

Here is the code

The Following way I am storing the data in an ArrayList<String>

private ArrayList<String> dataList; 
if (response.compareTo("Some Filter") != 0 //response is of String type
{
    dataList.add(response);
}

And in the below for each loop it throws OOM error

for (String s : dataList) { 
if(s.length()>8)
    dataList.set(dataList.indexOf(s), s.substring(8));  
else
    dataList.set(dataList.indexOf(s), "");
}

String downloadedData = "";
for (String s : dataList) {
    downloadedData += s; //This one is the 280th line throwing OOM
}

So far I have read this post but it gives solutions for reading data in json or web response

And i know OOM error can't be handled but prevented by following a good Architecture

And there are also these two Callbacks for Android

1. onLowMemory()
2. onTrimMemory()

But i am not sure how to go for the solution !!

The crash Stacktrace is:

java.lang.OutOfMemoryError: Failed to allocate a 106990 byte allocation with 5840 free bytes and 5KB until OOM
 at java.lang.AbstractStringBuilder.enlargeBuffer(AbstractStringBuilder.java:95)
 java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:146)
 at java.lang.StringBuilder.append(StringBuilder.java:216) 
 at Class_name.java:280.

Any help is appreciated :)

Answer 1

First: if (response.compareTo("Some Filter") != 0 ) that is just weird, you can just use equals method.

Then you are adding response to the list, and then you are reducing length of all responses in a list if they are higher than 8 (also, you did substring(8) , that trims the first 8 letters and I think you wanted to preserve first 8 letters and delete the rest, if yes then do this substring(0, 8) ).

My answer is: why not just take care of the things you are doing in a for-each when you are adding it to a list? It would be a lot easier and it would be better performance-wise, and would probably fix your error.

Also, I'm not sure if you are initializing your list, maybe you just forgot to paste it (all you have is private ArrayList<String> dataList; ), but that's how you make a new list:

List<String> list = new ArrayList<String>();

Answer 2

First your loop should use

for (int i = 0; i < dataList.size(); ++i) {
    String s = dataList.get(i);
    dataList.set(i, s.length() > 8 ? s.substring(8) : "");  
}

And the error points in another direction.

Answer 3

Try it is working

 ArrayList<String> dataList = new ArrayList<>();
 String response = "CVMKVLC";
    if (response.compareTo("Some Filter") != 0 ) {
         //response is of String type     
         dataList.add(response);
    }

    for (String s : dataList) { //This line throws OOM
       if(s.length()>8)
           dataList.set(dataList.indexOf(s), s.substring(8));
       else
           dataList.set(dataList.indexOf(s), "");
       }
    }