/**
     * Returns an array of stack trace elements representing the stack dump
     * of this thread.  This method will return a zero-length array if
     * this thread has not started, has started but has not yet been
     * scheduled to run by the system, or has terminated.
     * If the returned array is of non-zero length then the first element of
     * the array represents the top of the stack, which is the most recent
     * method invocation in the sequence.  The last element of the array
     * represents the bottom of the stack, which is the least recent method
     * invocation in the sequence.
     *
     * <p>If there is a security manager, and this thread is not
     * the current thread, then the security manager's
     * <tt>checkPermission</tt> method is called with a
     * <tt>RuntimePermission("getStackTrace")</tt> permission
     * to see if it's ok to get the stack trace.
     *
     * <p>Some virtual machines may, under some circumstances, omit one
     * or more stack frames from the stack trace.  In the extreme case,
     * a virtual machine that has no stack trace information concerning
     * this thread is permitted to return a zero-length array from this
     * method.
     *
     * @return an array of <tt>StackTraceElement</tt>,
     * each represents one stack frame.
     *
     * @throws SecurityException
     *        if a security manager exists and its
     *        <tt>checkPermission</tt> method doesn't allow
     *        getting the stack trace of thread.
     * @see SecurityManager#checkPermission
     * @see RuntimePermission
     * @see Throwable#getStackTrace
     *
     * @since 1.5
     */

    public StackTraceElement[] getStackTrace() {

  {- -------------------------------------------
  (1) 処理対象がカレントスレッドであれば, 新しい Exception オブジェクトを作り, 
      そこから java.lang.Throwable.getStackTrace() メソッドでスタックトレースを取得すればいいだけ.

      そうでなければ, (もし存在するなら SecurityManager によるチェックを行った後) 以下のように処理する.
      * 処理対象がもう死んでいる場合 (= isAlive() が false の場合)
        EMPTY_STACK_TRACE をリターンする
      * 処理対象がまだ生きている場合 (= isAlive() が true の場合)
        java.lang.Thread.dumpThreads() を呼んでスタックトレースを取得する.
        (StackTraceElement の配列が返ってくるので, その先頭要素だけを使用)
        結果が null でなければ, その結果をリターンする.
        結果が null であれば EMPTY_STACK_TRACE をリターンする.
      ---------------------------------------- -}

            if (this != Thread.currentThread()) {
                // check for getStackTrace permission
                SecurityManager security = System.getSecurityManager();
                if (security != null) {
                    security.checkPermission(
                        SecurityConstants.GET_STACK_TRACE_PERMISSION);
                }
                // optimization so we do not call into the vm for threads that
                // have not yet started or have terminated
                if (!isAlive()) {
                    return EMPTY_STACK_TRACE;
                }
                StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
                StackTraceElement[] stackTrace = stackTraceArray[0];
                // a thread that was alive during the previous isAlive call may have
                // since terminated, therefore not having a stacktrace.
                if (stackTrace == null) {
                    stackTrace = EMPTY_STACK_TRACE;
                }
                return stackTrace;
            } else {
                // Don't need JVM help for current thread
                return (new Exception()).getStackTrace();
            }
        }