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1. Top results related to why do we need a dictionary in java

   • Why do we need a default no argument constructor in Java?

     Top Answer

     Answered Mar 28, 2019 · 25 votes

     Java only provides a default no-argument constructor if no other constructors are defined. Thus, if you have other constructors you must explicitly define a no-arg constructor yourself.

     These frameworks use the reflection API and look at method names to determine how to set properties. The arguments of a constructor can only be found by type, not by name, so there is no way for the framework to reliably match properties to constructor args. Therefore, they require a no-arg constructor to create the object, then can use the setter methods to initialise the data.

     Some frameworks may support @ConstructorProperties

     as an alternative.

     Other Answers

     Answered Jun 20, 2020 · 11 votes

     I believe frameworks that require public nullary constructors do so because they use reflection to instantiate types, e.g. through Class.newInstance()

     .

     As to why the default constructor may not work for this case, here's the relevant JLS section:

     JLS 8.8.9 Default Constructor

     If a class contains no constructor declarations, then a default constructor that takes no parameters is automatically provided:

     • ["if the class "," is declared public ",", then the default constructor is implicitly given the access modifier public ",";"]
     • ["if the class is declared protected ",", then the default constructor is implicitly given the access modifier protected ",";"]
     • ["if the class is declared private ",", then the default constructor is implicitly given the access modifier private ",";"]
     • otherwise, the default constructor has the default access implied by no access modifier.

     So in a public class, the default constructor would have the right visibility, but otherwise an explicitly public one must be provided.

     Other Answers

     Answered Jun 20, 2010 · 4 votes

     A constructor is needed to initialise any non-default values and can contain side effects which are needed.

     If you have a programing style which encourages a minimal constructor for data transfer objects this would seem unneccasary, but the libraries have chosen not to assume any programming style for the constructors.

     You can write a library which doesn't assume a default constructor, but you have to make assumptions about what the constructor would do and wouldn't do. i.e. I have written such libraries but was able to also mandate what a constructor was allowed to do so that not calling it directly was safe.

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     1/5

   • Why do we need a Scanner Object for taking input in java

     Top Answer

     Answered Jul 08, 2017 · 3 votes

     System.in is simply an InputStream. A pretty generic interface designed many years ago. Changing this aspect would break a lot of existing code. So changing the type of System.in is a no go.

     Adding the scanner methods to the stream would bloat the existing class on the other hand. Think of concepts such as single responsibility principle or segregation of concerns.

     You see - good object oriented design is about having small classes that have one responsibility. Not two, not 5 or 10.

     But I think you have a certain point - and if Java would be rewritten today, that input stream might end up being more convenient.

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     2/5

   • Why do we need to install a kit (JDK) to start programming in Java

     Top Answer

     Answered Jan 30, 2016 · 1 votes

     The normal Java package (the JRE) only contains the stuff necessary to run Java programmes. The JDK is the package containing the compiler. Based on your experience with Pascal and C++, you obviously understand why you need the compiler to create your own programmes.

     Eclipse and Netbeans are IDEs, Integrated Developement Enviroments. They make it easier for you to program, but they are not strictly needed, in the same way that you can write a program in C++ by just installing a C++ compiler and without using Visual Studio. There are many programmers, especially in the non-windows-world, who just use a text editor to write those programmes.

     As for Python and Perl, it's the same thing. You need to install their respecitve interpreters to run programmes written in those languages. Without them, how do you expect the computer to understand what you want from it?

     If you want compare, for example, Eclipse and Visual Studio: the installation for Visual Studio contains both the IDE and the compiler. Eclipse is just the IDE. You also need to install the compiler, which is contained in the JDK.

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     3/5

   • Why do we need multiple constructors for defining a binary tree in Java?

     Top Answer

     Answered Jul 17, 2014 · 0 votes

     Running the code simply with only public IntTreeNode(int data, IntTreeNode left, IntTreeNode right) would be perfectly legal code.

     The 2 constructors here are for convenience. For a leaf node, it is not possible to have subtrees. Therefore, the one-parameter constructor provides a convenient way to add a leaf node, with the subtrees defaulted to null. On the other hand, any non-leaf node can have up to 2 subtrees, and so the second constructor exists to create such nodes.

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     4/5

   • Why do we need a temporary node while inserting values in a node in Linked list?

     Top Answer

     Answered May 22, 2021 · 0 votes

     Why do we need a temporary node while inserting values in a node in Linked list?

     Because you are traversing to the leaves of the tree here:

     while (current_node.left != null) { current_node = current_node.left;}current_node.left = newnode;height += 1;

     In these lines of code, you are trying to find the leftmost leaf so as to insert newnode, right? You want to use a variable to keep track of which node you are currently on, and "go left" by doing someVariable = someVariable.left;.

     You could use root to keep track of where you are at, but root already has a purpose - to record the root of the tree! If you did root = root.left;, you are making the left node of the original root be the new root! Say your tree was:

     50 / \ 10 100-

     Doing root = root.left deletes most of it:

     10-

     This is problematic because this means your tree essentially "forgets" about a part of the tree. Technically, The 50 and 100 nodes still exists and 50 is still connected to 10, but your binary_tree object doesn't have access to it anymore. The only point of access it has is root, which you have now set to the node 10.

     What actually happens in your program is: it correctly inserts 50, 10, and 100, then when adding 5, tries to traverse down the left subtree. This makes the root "10", and adding 5 becomes:

     10 / 5-

     It then adds 1000 correctly:

     10 / \ 5 1000-

     Hence it prints 10 and 1000.

     Using a brand new variable solves this problem, because the brand new variable has nothing to do with root.

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     5/5

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2. stackoverflow.com › questions › 13543457How do you create a dictionary in Java? - Stack Overflow

   stackoverflow.com › questions › 13543457

   • Cached

   I am trying to implement a dictionary (as in the physical book). I have a list of words and their meanings. What data structure / type does Java provide to store a list of words and their meanings as key/value pairs. How, given a key, can I find and return the value?

   Code sample

   Map<String, String> map = new HashMap<String, String>();

   map.put("dog", "type of animal");

   System.out.println(map.get("dog"));

   See more on stackoverflow

3. thelinuxcode.com › create-a-dictionary-in-javaThe Complete Guide to Effectively Using Dictionaries in Java

   thelinuxcode.com › create-a-dictionary-in-java

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   Dec 27, 2023 · Dictionaries are a fundamental data structure in programming used to map keys to values for efficient lookup and organization. Mastering dictionaries is key to writing optimized Java code. In this comprehensive guide, you‘ll learn all about dictionaries and how to leverage them in your Java programs like a pro! We‘ll cover: What dictionaries are and … The Complete Guide to Effectively ...

4. People also ask

   What is dictionary in Java?

   • Dictionary in Java is an abstract class in Java that stores the data in the form of key-value pairs. It is found in the java.util package and works similar to a Map. Each key has a value and we can retrieve the values in a Dictionary object using its corresponding key. We can declare a dictionary object in Java in the below way:

   Dictionary in Java - Java Dictionary - Java Dictionary class - TutorialCup

   tutorialcup.com/java/dictionary-in-java.htm

   See all results for this question

   How to add a key to a dictionary in Java?

   • Some of the important methods are: put (Object key, Object value): This method adds a key-value pair to the dictionary. If the key already exists in the dictionary, the value associated with the key is replaced with the new value. get (Object key): This method returns the value associated with the specified key.

   Dictionary Class in Java - Java To The Point

   javatothepoint.com/dictionary-class-in-java/

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   How to retrieve a value from a dictionary object in Java?

   • You can store the value in a Dictionary object and once it is stored, you can retrieve it by using its key. Let us have a look at a few different methods of Dictionary Class. isEmpty () : java.util.Dictionary.isEmpty () checks whether the dictionary is empty or not.

   Dictionary in Java | How to Create Java.util.Dictionary Class - Edureka

   www.edureka.co/blog/dictionary-in-java/

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   What is a dictionary class?

   • The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values. Every key and every value is an object. In any one Dictionary object, every key is associated with at most one value. Given a Dictionary and a key, the associated element can be looked up.

   Dictionary (Java SE 21 & JDK 21) - docs.oracle.com

   docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Dictionary.html

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5. javatothepoint.com › dictionary-class-in-javaDictionary Class in Java - Java To The Point

   javatothepoint.com › dictionary-class-in-java

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   • Features of Dictionary Class
   • Creating A Dictionary Object
   • Conclusion

   The Dictionary class provides methods for adding, removing, and retrieving key-value pairs. Some of the important methods are: 1. put(Object key, Object value): This method adds a key-value pair to the dictionary. If the key already exists in the dictionary, the value associated with the key is replaced with the new value. 2. get(Object key): This ...

   See full list on javatothepoint.com

   To use the Dictionary class, you must create an instance of it. However, the Dictionary class is an abstract class, so you cannot create an instance of it directly. Instead, you must create an instance of one of its concrete subclasses, such as Hashtable or Properties.

   See full list on javatothepoint.com

   The Dictionary class is a useful tool for managing key-value pairs in Java. While it is a legacy class, it is still supported and used in many legacy applications. The Dictionary class provides a way to add, remove, and retrieve key-value pairs, and it is the superclass of the Hashtable and Properties classes.

   See full list on javatothepoint.com

6. thelinuxcode.com › java-dictionaryAn In-Depth Guide to Using Dictionaries in Java – TheLinuxCode

   thelinuxcode.com › java-dictionary

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   Nov 8, 2023 · Dictionaries are a critical data structure in many programming languages, allowing you to store and retrieve data as key-value pairs. In Java, the Dictionary abstract class provides a useful implementation of a hash table-backed dictionary. In this comprehensive guide, we‘ll cover everything you need to effectively use dictionaries in your Java applications. What is a … An In-Depth Guide ...

7. tutorialcup.com › java › dictionary-in-javaDictionary in Java - Java Dictionary - Java Dictionary class

   tutorialcup.com › java › dictionary-in-java

   • Cached

   Dictionary in Java is an abstract class in Java that stores the data in the form of key-value pairs. It is found in the java.util package and works similar to a Map. Each key has a value and we can retrieve the values in a Dictionary object using its corresponding key.

8. docs.oracle.com › java › utilDictionary (Java SE 21 & JDK 21) - docs.oracle.com

   docs.oracle.com › java › util

   • Cached

   The Dictionary class is the abstract parent of any class, such as Hashtable, which maps keys to values. Every key and every value is an object. In any one Dictionary object, every key is associated with at most one value. Given a Dictionary and a key, the associated element can be looked up.

9. www.edureka.co › blog › dictionary-in-javaWhat is Dictionary in Java and How to Create it? - Edureka

   www.edureka.co › blog › dictionary-in-java

   • Cached

   Jun 17, 2021 · Dictionary is an abstract class representing a key/value storage repository that operates like Map. You can store the value in a Dictionary object and once it is stored, you can retrieve it by using its key.