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What is the common method of Map collection in Java? I believe many inexperienced people don't know what to do about it. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

The difference between Map collection and Collection collection

The Map collection has Key and Value, and the Collection collection has only Value.

There are also Key and Value at the bottom of the Collection collection, but they are hidden.

1. V put (K key, V value)

Add an element with Key as key,Value and value to the map collection, and return null if the addition is successful, or value if it is successful.

That is to say, the Key in the Map collection cannot be repeated, just like the elements in the Set collection cannot be repeated, but the Value in the Map collection can be repeated.

2. Void putAll (Map

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