源码看JAVA【三十六】AbstractQueue

AbstractQueue抽象类，实现了Queue接口的部分通用方法。

1、add：调用offer方法实现，不存在false的情况，false直接抛出异常

    /**
     * Inserts the specified element into this queue if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
     * if no space is currently available.
     *
     * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
     * else throws an <tt>IllegalStateException</tt>.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws