Why is java.io.FileDescriptor's constructor public?

java

Solution

This constructor is public because it is used outside of `java.io`.

Classes using `new FileDescriptor()` in JRE 7u4 Linux x86:

java.io.FileInputStream
java.io.FileOutputStream
java.io.RandomAccessFile

java.lang.UNIXProcess
java.net.AbstractPlainDatagramSocketImpl
java.net.AbstractPlainSocketImpl
java.net.ServerSocket

sun.net.sdp.SdpSupport
sun.nio.ch.FileChannelImpl
sun.nio.ch.FileDispatcherImpl
sun.nio.ch.IOUtil
sun.nio.ch.PipeImpl
sun.nio.ch.SctpServerChannelImpl
sun.nio.ch.ServerSocketChannelImpl
sun.nio.ch.UnixAsynchronousServerSocketChannelImpl
sun.nio.fs.UnixChannelFactory

There is a `sun.misc.SharedSecrets` method that allows the programmer to change the state of a `FileDescriptor` to a valid one (this snippet found in `java.io.FileDescriptor`):

  static {
        sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
            new sun.misc.JavaIOFileDescriptorAccess() {
                public void set(FileDescriptor obj, int fd) {
                    obj.fd = fd;
                }

                public int get(FileDescriptor obj) {
                    return obj.fd;
                }

                public void setHandle(FileDescriptor obj, long handle) {
                    obj.handle = handle;
                }

                public long getHandle(FileDescriptor obj) {
                    return obj.handle;
                }
            }
        );
    }

This means that any code that can access `SharedSecrets` (I.E. the JRE itself) can also create its own valid `FileDescriptor`, and should therefore be allowed to access `FileDescriptor()`. However, there is no way to restrict the access of a constructor to only JRE classes, so it is public.

Problem

Original source