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add()：增加一个元素。如果队列已满，则抛出一个IIIegaISlabEepeplian异常

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throw IllegalStateException or return false.

offer()：添加一个元素并返回true。如果队列已满，则返回false

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never return false.

分析

• 两者都是往队列尾部插入元素
• 当超出队列界限的时候，add()方法是抛出异常让你处理，而offer()方法是直接返回false