Java中几个容易犯错的地方

1，byte[]的长度

写了一个从文件里读字符串的函数：

public static String readFile(String fFileName){//, String fEncoding) {

        char[] buffer = new char[1024];
        StringBuilder text = new StringBuilder();
        InputStreamReader reader = null;
        try {
            reader = new InputStreamReader(new FileInputStream(fFileName));
            while (reader.read(buffer, 0, 1024)!=-1){
                text.append(buffer);  <==有错
            }
        }
        catch(Exception e){
            e.printStackTrace();
        }
        finally{
            if(reader!=null){
                try {
                    reader.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        return text.toString();
    }

粗看这段代码没有问题。但是读出的字符总比实际要多。问题在text.append(buffer)。 buffer是一个1024的char数组。每次append固定的1024个char。改成就好了。

        reader = new InputStreamReader(new FileInputStream(fFileName));
        int readed;
        while ((readed = reader.read(buffer, 0, 1024))!=-1){
            text.append(new String(buffer, 0, readed));
        }

2，优先级的错误

Log.d(TAG, "location="+where+", "+locationService==null?"null":locationService.getLocation());

这行代码的本意是如果locationService==null，就输出“null”,避免NullPointerException。但实际上仍然发生NullPointerException。原来"+"的优先级大于"?",所以上面代码实际上是：

Log.d(TAG, ("location="+where+", "+locationService)==null?"null":locationService.getLocation())

括号里的当然不会是null。改成

Log.d(TAG, "location="+where+", "+(locationService==null?"null":locationService.getLocation()));

就好了。