In Java, a Hashset, theoretically, cannot contain any duplicate values but it is not valid when you store user defined objects in it. Same is true in case of Hashmap keys which supposedly cannot be The reason is, how will Java interpreter know if our custom defined objects are equivalent or different? Java Syntax, 8 уровень, 8 лекция. The Object.keys() method returns an array of a given object's own enumerable property names, iterated in the same order that a normal loop would. The ordering of the properties is the same as that given by looping over the properties of the object manually. Manually edit the registry (Use this only if the Fix It utility does not work). Incorrectly editing your registry may severely damage your system. You can use the File->Export functionality of the registry editor to save the registry key before deleting. The Object keys() method is used to return the array whose elements are strings corresponding to the enumerable properties found directly upon the object. An ordering of the properties is the same as that given by an object manually in the loop is applied to the properties. Working with both object-oriented software and relational databases can be time consuming. Due to a paradigm mismatch between how data is represented in objects (which are usually nonscalar values) versus relational databases (where scalar values are organized in tables) I want to delete a node of the Tree through its reference in HashMap. I tried this one: Iterator iter = pHash.keySet().iterator() Whenever you no longer need to use an Object in Java, if you simply get rid of any references to that Object, Garbage collection will take care of it from there. Specify both the object's key name and a version ID to be deleted. Amazon S3 will delete the specified version of the object. The example uploads sample objects to the bucket and then uses the AmazonS3Client.deleteObjects() method to delete the objects in a single request. 1. Overview. In this tutorial, we're going to explore the available options for handling a Map with duplicate keys or, in other words, a Map which allows storing multiple values for a single key. 2. Standard Maps. Object.keys, values, entries. For plain objects, the following methods are available The first difference is that we have to call Object.keys(obj), and not obj.keys(). Why so? The main reason is flexibility. The Key interface is the top-level interface for all keys. It defines the functionality shared by all key objects. This is an external encoded form for the key used when a standard representation of the key is needed outside the Java Virtual Machine, as when transmitting the key to some other party.