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# Troubleshooting Tips

- A `File` object represents a file name, not an actual file. Such objects are, moreover, immutable. Thus the code

          File f1 = new File("foo");
          File f2 = new File("bar");
          f1.renameTo(f2);

  will rename the file named `"foo"` (if it exists) to `"bar"`. It will not change the value of the `File` object referred to by `f1`; in particular, the expression `f1.getPath()` will still evaluate to `"foo"`.
- The `available` method of the `InputStream` class and its subclasses does not necessarily return the maximum number of bytes that can be read without blocking. In particular, code of the form

          int n = in.available();
          byte buf = new byte[n];
          in.read(buf);

  is not guaranteed to read all of the remaining bytes from the given input stream. Similarly, the `ready` method of `Reader` and its subclasses may return `false` even if the stream is ready to be read.
- The `read(byte[])` and `read(byte[], int, int)` methods of `InputStream` and its subclasses are not guaranteed to read all available bytes. A loop may be required, for example, in order to read a large file into an array:

          for (int off = 0; off < size;) {
              int r = in.read(buf, off, buf.length - off);
              if (r == -1) break;
              off += r;
          }

  Alternatively, a `BufferedInputStream` may be used. Similar remarks apply to the `read(char[])` and `read(char[], int, int)` methods of `Reader` and its subclasses.
- The `PrintStream` and `PrintWriter` classes suppress all I/O errors. To see whether an error has occurred, invoke the `checkError` method.
- `PrintStream` and `PrintWriter` objects do not always flush their output. To arrange for automatic flushing, use the two-argument constructors of these classes and specify `true` for the second argument.

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