Java Top Tips - 1

1. Flush Streams

This might seem obvious, but it repeatedly kicks my butt. The problem usually appears with two programs on either side of a network socket having some kind of conversation. If you don't flush the output stream every time you say something, the data may not actually get written out to the socket, and the two programs will sit patiently, waiting forever for something to happen.

Typically, you can just call flush() after you write something important:

      // OutputStream out;
      // byte[] data
      out.write(data);
      out.flush();

If you're writing text data, you might use a PrintWriter for output. PrintWriter has a special constructor that lets you specify if the stream should be flushed after every newline:

     PrintWriter out = new PrintWriter(rawOut, true);

A PrintWriter created in this way will automatically flush itself whenever you write a line of text.
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2. Use Double Equals for Comparisons

This is a holdover from C. It made its way into C++, and then Java used a lot of C++ syntax. The bug goes like this: Somewhere, you accidentally type a single equals sign instead of a double one when examining a boolean value:

      boolean b = false;
      if (b = true) {
            // Always gets executed.
      }
 
Instead of performing a comparison, as you'd hoped, you're actually assigning true to the variable b. This assignment has an overall value of true, so the if always succeeds.
Some people suggest reversing the order of the comparison, so the literal value always comes first. This generates a compile-time error for if (true = b), so you'll figure out what's wrong and change it to if (true == b). Personally, I don't like how this looks, so I just muddle through the old fashioned way, making darn sure I always use a double equals when I need it.
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