Java文档映射接口描述
地图界面描述中的一段
Many methods in Collections Framework interfaces are defined in terms of the equals method. For example, the specification for the containsKey(Object key) method says: "returns true if and only if this map contains a mapping for a key k such that (key==null ? k==null : key.equals(k))."
为什么他们不使用(key==null?true:key.equals(k))而不是(key==null?k==null:key.equals(k))
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