Java Notes - Page 5

An Iterator walks a collection one element at a time, and it is the only safe way to remove during a traversal.

A Queue processes elements in an order it decides. A Deque works at both ends, and it is the right way to build a stack in Java.

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Buckets, hashing, collisions and resizing. Understanding the mechanism explains the performance and every rule about keys.

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A Map stores key to value pairs with unique keys, and it is the collection you will reach for most often.

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A Set stores unique elements. The three implementations differ in ordering and in what uniqueness is based on.

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A List keeps insertion order and allows duplicates. ArrayList is the default; LinkedList wins only at the ends.

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A small set of interfaces describes how groups of objects behave, and many implementations trade memory, ordering and speed differently.

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The rules that separate exception handling which helps from exception handling which hides bugs.

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A custom exception names a failure in the language of your domain, which makes handling precise and messages meaningful.

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throw raises an exception now; throws declares that a method may raise one and leaves the handling to the caller.

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try guards a block, catch handles specific failures, finally always runs, and try with resources closes what you opened.

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Errors, checked exceptions and unchecked exceptions sit in one hierarchy, and knowing which is which decides how you should react.