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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

   This creates dictionary of text (string): Map<String, String> dictionary = new HashMap<String, String>(); you then use it as a: dictionary.put("key", "value"); String value = dictionary.get("key"); Works but gives an error you need to keep the constructor class same as the declaration class.

3. docs.oracle.com › api › javaDictionary (Java Platform SE 8 ) - Oracle

   docs.oracle.com › api › java

   • 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. Any non- null object can be used as a key and as a value.

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

   What happened to the Java Dictionary class?

   • The Java Dictionary class has now become obsolete and currently all the collection types that store data in the form of key-value pairs implement the Java Map interface. However, the Java Dictionary class variables can still be used to store a reference to the Hashtable classes implementing the Map interface.

   Understanding the Java Dictionary Class - Udemy Blog

   blog.udemy.com/java-dictionary/

   See all results for this question

   How to create a dictionary in Java?

   • The Dictionary object classes are implemented in java.util. The first step to creating a dictionary in Java is to choose a class that implements a “key-value pair” interface; a few examples include HashTables , HashMap, and LinkedHashMap. The declaration and initialization of a dictionary follows the syntax below:

   How to create a dictionary in Java - queslers.com

   queslers.com/how-to-create-a-dictionary-in-java/

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   What is the difference between dictionary and map in Java?

   • Dictionary is an abstract class whereas Map is an interface, hence it is more Java-idiomatic. Dictionary was deprecated early in Java 1.2 and replaced by its better interface counterpart, Map. This leads to believed that Dictionary was just a bad design choice and the Java folks kept the Dictionary class for backward compatibility.

   What is the difference between the Dictionary class and the Map class

   stackoverflow.com/questions/25900226/what-is-the-difference-between-the-dictionary-class-and-the-map-class-in-java

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5. docs.oracle.com › util › class-useUses of Class java.util.Dictionary (Java Platform SE 8 ) - Oracle

   docs.oracle.com › util › class-use

   • Cached

   Description. java.security. Provides the classes and interfaces for the security framework. java.util. Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array). javax.swing.

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

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

   • Cached

   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 ...

7. 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 ...

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

   tutorialcup.com › java › dictionary-in-java

   • Cached

   • Initializing A Dictionary Object
   • Example of Java Dictionary Methods
   • Conclusion

   To initialize a dictionary object, we can use either a Hashtable, HashMap or LinkedHashMap. obj– Dictionary object Type– represents the type of key and value Every key has a corresponding value and both the key and value cannot have null values. The below diagram shows the key-value pair association.

   See full list on tutorialcup.com

   In the below example, we have used all the methodsof the Dictionary class in Java. To use the Dictionary class, we need to import the java.util.Dictionary package. The put() method inserts the key-value pair data into the Dictionary object. To retrieve the size, we use the size() method. The get()method retrieves the value of the corresponding key ...

   See full list on tutorialcup.com

   In this tutorial, we have seen how to use the Dictionary class to store the key-value pairs by implementing using the Hashtable. We have also seen how to use the various methods present in the Dictionary class. Reference

   See full list on tutorialcup.com

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

   javatothepoint.com › dictionary-class-in-java

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   May 10, 2023 · In Java, a dictionary is a data structure that stores key-value pairs. The Java API provides the Dictionary class to implement a dictionary. The Dictionary class is an abstract class that defines a data structure for managing key-value pairs. It is the superclass of the Hashtable and Properties classes.