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1. Top results related to 2 types of dictionary in java

   • Dictionary of ArrayLists in Java

     Top Answer

     Answered Jun 05, 2012 · 2 votes

     Instead of ArrayList grades; you'd have to use ArrayList grades = new ArrayList();

     Yet better: ArrayList<Float> grades = new ArrayList<Float>(); //or use Double or Number

     Note that unlike C or C++ creating a variable doesn't create the object as well. In C++ you could imagine your code as ArrayList* grades; i.e. you'd just create the reference/pointer here.

     Additional thoughts:

     • Dictionary studentGrades; this will be initialized to null.
     • public void main(String[] args) that's not a valid main function since it would have to be static
     • if you have a public static void main(String[] args) you can't use this since you don't have an object instance in the static context
     • You can't instantiate Dictionary since it is abstract. Use one of its subclasses, e.g. new Hashtable<String, List<Float>>(), or a map, e.g. Map<String, List<Float> dictionary = new HashMap<String, List<Float>>();
     • Note that local primitive variables are also not initialized, so this could give you an error too: boolean res; In Java only class members are initialized, local variables are not.

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   • Types of References in Java

     In Java there are four types of references differentiated on the way by which they are garbage collected.

     • Strong References
     • Weak References
     • Soft References
     • Phantom References

     Prerequisite: Garbage Collection

     MyClass obj = new MyClass (); -

     obj = null;//'obj' object is no longer referencing to the instance. So the 'MyClass type object is now available for garbage collection. -

     // Java program to illustrate Strong reference class Gfg {     //Code.. } public class Example {     public static void main(String[] args)     {          //Strong Reference - by default         Gfg g = new Gfg();                       //Now, object to which 'g' was pointing earlier is          //eligible for garbage collection.         g = null;      } }  -

     If JVM detects an object with only weak references (i.e. no strong or soft references linked to any object object), this object will be marked for garbage...

     • This type of reference is used in WeakHashMap to reference the entry objects .
     • If JVM detects an object with only weak references (i.e. no strong or soft references linked to any object object), this object will be marked for garbage collection.

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     2/5

   • Types of Classes in Java

     A class is a blueprint in the Java programming language from which an individual object can be built. In Java, we may declare a class by using the class keyword. Class members and functions are declared simply within the class. Classes are required for the creation of Java programs. The object-oriented paradigm (OOP) allows users to describe real-world objects. Also, a class is sometimes known as a user-defined data type. The following components make up a class declaration:

     • Modifiers
     • Class name
     • Keywords
     • The class body within curly brackets {}.

     Class in Java  

     1. Class is a set of object which shares common characteristics/ behavior and common properties/ attributes. 2. Class is not a real world entity. It is just a template or blueprint or prototype from which objects are created. 3. Class does not occupy memory. 4. Class is a group of variables of different data types and group of methods.

     A class in java can contain: • data member • method • constructor • nested class and  • interface

     Syntax to declare a class:...

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     3/5

   • Types of Interfaces in Java

     In Java, an interface is a reference type similar to a class that can contain only constants, the method signatures, default methods, and static methods, and its Nested types. In interfaces, method bodies exist only for default methods and static methods. Writing an interface is similar to writing to a standard class. Still, a class describes the attributes and internal behaviors objects, and an interface contains behaviors that a class implements. On the other side unless the class that implements the interface is purely abstract and all the interface methods need to be defined in that given usable class.

     An interface is Similar To a Class In Following Ways:

     • An interface can contain any number of methods in that interface.
     • An Interface can have constant values, which are implicitly defined as public static final.

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     4/5

   • Types of Thread Pools in java

     Top Answer

     Answered Jun 30, 2013 · 42 votes

     There are various thread pools in java:

     • Single Thread Executor : A thread pool with only one thread. So all the submitted tasks will be executed sequentially. Method : Executors.newSingleThreadExecutor()
     • Cached Thread Pool : A thread pool that creates as many threads it needs to execute the task in parrallel. The old available threads will be reused for the new tasks. If a thread is not used during 60 seconds, it will be terminated and removed from the pool. Method : Executors.newCachedThreadPool()
     • Fixed Thread Pool : A thread pool with a fixed number of threads. If a thread is not available for the task, the task is put in queue waiting for an other task to ends. Method : Executors.newFixedThreadPool()
     • Scheduled Thread Pool : A thread pool made to schedule future task. Method : Executors.newScheduledThreadPool()
     • Single Thread Scheduled Pool : A thread pool with only one thread to schedule future task. Method : Executors.newSingleThreadScheduledExecutor()

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     5/5

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2. www.geeksforgeeks.org › java-util-dictionary-classJava.util.Dictionary Class in Java - GeeksforGeeks

   www.geeksforgeeks.org › java-util-dictionary-class

   • Cached

   Apr 9, 2023 · The java.util.Dictionary class in Java is an abstract class that represents a collection of key-value pairs, where keys are unique and are used to access the values. It was part of the Java Collections Framework introduced in Java 1.2 but has been largely replaced by the java.util.Map interface since Java 1.2.

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

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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 Platform SE 8 ) - docs.oracle.com

   docs.oracle.com/javase/8/docs//api/java/util/Dictionary.html

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   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 do dictionaries work in Java?

   • To truly grasp the working of Java dictionaries, it’s essential to understand the concept of hashing. Hashing is a process that takes an input (or ‘message’) and returns a fixed-size string of bytes, typically in the form of a ‘hash code’.

   Java Dictionary | Hashmaps and Hashtables Guide

   ioflood.com/blog/java-dictionary/

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5. ioflood.com › blog › java-dictionaryJava Dictionary | Hashmaps and Hashtables Guide

   ioflood.com › blog › java-dictionary

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   Nov 9, 2023 · Think of Java’s HashMaps and Hashtables as a real-world dictionary, allowing us to store and retrieve data based on unique keys. These tools are incredibly versatile and handy for various tasks. This guide will walk you through the creation, usage, and manipulation of dictionaries in Java.

6. www.toolsqa.com › java › dictionary-classDictionary Class in Java | Dictionary usage in Java - Tools QA

   www.toolsqa.com › java › dictionary-class

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   Jul 27, 2021 · Data Structures - ArrayList. Next Lesson. HashTable class. The Dictionary class. In Java, a Dictionary is an abstract class that maps keys to values. Both keys and values can be objects of any type but not null. An attempt to insert either a null key or a null value to a dictionary causes a NullPointerException exception.

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

   tutorialcup.com › java › dictionary-in-java

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

   docs.oracle.com › util › class-use

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   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.

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 · 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.