Java Tutorial

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java BufferedWriter Java InputStreamReader Java File Java Read File Line By Line Java FileOutputStream Jar File in Java

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java

Hashtable in Java

Hashtable in Java

The Hashtable class implements the Map interface and extends the Dictionary class. It implements a hash table which shows the key-value relation, i.e., it maps the keys to the values. Hashtable contains bucket (index) to store the key-value pair. The key’s hashcode is used to determine to which bucket the key-value pair should be mapped.

  • Hashtable is similar to HashMap, but it is synchronized whereas HashMap is not.
  • The object that is used as a key or as a value must not be null.
  • For successful storing and fetching of the object from the Hashtable, the object must implement the hashcode() and the equals() methods.
  • The hash function is used to get a bucket location from the key’s hashcode. A hash function always returns a number for an Object.

Let’s take the hashtable with & buckets :

Hashtable in Java

The performance of the hashtable is affected by its two parameters, i.e., initial capacity and load factor.

Initial Capacity-The number of buckets in the hashtable denotes its capacity. And the initial capacity is the capacity at the time hashtable is created. If the initial capacity is larger than the maximum number of entries the hashtable then, the rehash operation will not occur. The tradeoff between wasted space and requirement of rehash operation is controlled by initial capacity.

Load Factor-It is a measure of space acquired by the hashtable that is allowed to get before its capacity is automatically increased.

If we need to insert a large number of entries into the hashtable, it is better to create it with large capacity. It allows the values to be inserted more efficiently than letting it to perform automatic rehashing as required to grow the table.

Constructors of Hashtable

Constructor Description
Hashtable() It creates an empty hashtable with an initial default capacity of 11 and a load factor of 0.75.
Hashtable(int initialCapacity) It creates an empty hashtable with an initial capacity specified in the arguments with the default load factor of 0.75.
Hashtable(int initialCapacity, float loadFactor) It creates an empty hashtable with initial capacity and load factor specified in the argument.
Hashtable(Map t) It creates a new hashtable with the same mapping properties as given in the specified map in the arguments.

Methods of Hashtable

Modifier and Data type Methods Description
void Clear() It removes all the key-values from the hash table.
  forEach(BiConsumer action) It performs the specified action for each element in the map until all the elements have been processed or it throws an exception.
  replaceAll(BiFunction function) It replaces all the values of the entry with the result of invoking the specified function on that particular entry until all entries have been processed or the specified function throws an exception.
boolean contains(Object value) It tests the keymaps into the specified value in the hashtable or not.
  containsKey(Object key) It tests if the object specified in the argument is a key in the hashtable.
  containsValue(Object value) It returns true if the hashtable maps one or more keys to the specified value.
  equals(Object o) This method compares the argumented object with the map to check equality, according to the definition in the Map interface.
  isEmpty() This method tests if the hashtable didn’t map any keys to values
  remove(Object key, Object value) If the specified key is mapped to the specified value then only the entry gets removed by this method.
  replace(K key, V oldValue, V newValue) If the specified key is currently mapped to the specified value, the entry gets replace with the specified new value.
int hashCode() According to Map interface, it returns the hash code value of the map.
  size() It returns the number of keys in the hashtable.
String toString() It returns the string equivalent of the hashtable object in the form of a set of key-value pairs.
Object clone() It creates a shallow copy of the hashtable.
V compute(K key, BiFunction remappingFunction) It calculates the mapping for the specified key and its current mapped value or returns null if there is currently no mapping.
  computeIfAbsent(K key, Function mappingFunction) It attempts to compute the specified key’s value using the argumented mapping function if the key is not already associated with any value (or is mapped to null).
  computeIfPresent(K key, BiFunction remappingFunction) If the key specified in the argument is associated with any value, then it attempts to compute a new mapping with the key and its current mapped value.
  get(Object key) It returns the value that is associated with the specified key or returns null if the map does not contain mapping for the specified key.
  getOrDefault(Object key, V defaultValue) It returns the defaultValue specified in the argument if the map doesn’t contain a mapping for the specified key.
  Merge(K key, V value, Bifunction remapping) This method assigns the given non-null value to the specified key if the key is not already associated with any value or mapped to null.
  put(K key, V value) This method maps the specified value to the specified key.
Void putAll(Map t) It copies all the mappings from the map specified in the argument to the hashtable.
V putIfAbsent(K key, V value) This method assigns the given value to the specified key and return null if the key doesn’t contain any value, else returns the current value.
  remove(Object key) It removes the specified key-value pair from the hashtable.
  replace(K key, V value) It replaces the value of the specified key if it is currently mapped to some value.
protected void rehash() It increases the capacity of the hashtable and internally reorganizes it.
Enumeration <V> elements() Returns the list of the values available in the hashtable.
Ser<Map.Entry<K,V>> entrySet() It returns a “Set” view of the mapping contained in this map.
Enumeration<K> keys() It returns the list of the keys in the hashtable.
Set<K> keyset() This method gives a “Set” view of the keys contained in the map.
Collection<V> values() This method gives a “Collection” view of the values associated in the map.

Example to illustrate clear() and clone() method:

import Java.util.*; 
 class HashClearDemo { 
     public static void main(String[] arg) 
     { 
         //initializing hash table 
         Hashtable<Integer, String> h1 = new Hashtable<Integer, String>(); 
         Hashtable<Integer, String> h2 = new Hashtable<Integer, String>(); 
         h1.put(1, "Java");  
         h1.put(2, "JavaScript"); 
         h1.put(3, "Oracle"); 
         // create a clone or shallow copy of hash table h 
         h2 = (Hashtable<Integer, String>)h1.clone(); 
         // printing entries in cloned hashmap 
         System.out.println("Entries in clone HashTable: " + h2); 
         // clearing hash table using clear() method  
         h1.clear(); 
         // checking hash table h 
         System.out.println("After using clear(): " + h1); 
     } 
 }  

Output:

Entries in clone HashTable: {3=Oracle, 2=JavaScript, 1=Java}
After using clear(): {} 

Example to illustrate forEach(BiConsumer action) method:

import Java.util.*; 
 public class ForEachDemo { 
     public static void main(String[] args) 
     { 
         // creating a hashtable 
         Map<String, Integer> price = new Hashtable<>(); 
         //adding entries to the table
         price.put("Sweets", 50); 
         price.put("Dosa", 60); 
         price.put("Icecream", 20);  
         price.put("Salat", 80); 
         price.put("Fruits", 100); 
         // increasing 50 price for every product using forEach() 
         price.forEach((k, v) -> 
         {   
             v = v + 50; 
             price.replace(k, v); 
         }); 
         // printing new mapping using forEcah() method 
         price.forEach( 
             (k, v) -> System.out.println(k + ", price : " + v)); 
     }  
 }  

Output:

Sweets, price : 100
Icecream, price : 70
Salat, price : 130
Fruits, price : 150
Dosa, price : 110 

Example to demonstrate computeIfAbsent(Key, Function) method.

import Java.util.*; 
 class AbsentDemo { 
     public static void main(String[] args) 
     { 
         // create a table and add some values 
         Map<Integer, String> t = new Hashtable<>();  
         t.put(1, "Java"); 
         t.put(2, "Spring"); 
         t.put(3, "Hibernate"); 
         // printing map details 
         System.out.println("HashTable: "+ t.toString()); 
         // adding new key-value pair using computeIfAbsent method 
         t.computeIfAbsent(4, k -> "Pyhton"); 
         // this will not affect anything in the hash table because key 1 already exist
         t.computeIfAbsent(1, k -> "Oracle"); 
         // print new mapping 
         System.out.println("New hashTable: "+ t);  
     } 
 } 

Output:

hashTable: {3=Hibernate, 2=Spring, 1=Java}
new hashTable: {4=Pyhton, 3=Hibernate, 2=Spring, 1=Java} 

Example to illustrate the isEmpty() method

import Java.util.*; 
 class EmptyDemo { 
     public static void main(String[] args) 
     { 
         // creating an empty Hashtable 
         Hashtable<String, Integer> h1 = new Hashtable<String, Integer>();
         Hashtable<String, Integer> h2 = new Hashtable<String, Integer>(); 
         // adding elements into the table 
         h1.put("Java", 10); 
         h1.put("Python", 15); 
         h1.put("pytorch", 20); 
         h1.put("Salesforce", 25); 
         h1.put("AWS", 30);  
         // printing the Hashtable 
         System.out.println("Elements in 1st table are: " + h1);
         System.out.println("Elements in 2nd table are: " + h2);
         // checking if the table is empty 
         System.out.println("First table is empty !! " + h1.isEmpty());
         System.out.println("Second table is empty !!" + h2.isEmpty()); 
     } 
 } 

Output:

Elements in 1st table are: {Java=10, AWS=30, Python=15, Salesforce=25, pytorch=20}
Elements in 2nd table are: {}
First table is empty!! False
Second table is empty!!True 

Example to demonstrate compute(Key, BiFunction) method.

import Java.util.*; 
 class computeDemo { 
     public static void main(String[] args) 
     { 
         // creating a table and adding some tutorial and its fees
         Map<String, Integer> h = new Hashtable<>();  
         h.put("Java", 10000); 
         h.put("Python", 12000); 
         h.put("AWS", 18000); 
         h.put("Salesforce", 8000); 
         // printing map details 
         System.out.println("Tutorial price: " + h.toString());  
         // remapping the values of hashTable using compute method 
         h.compute("Java", (key, val) 
                                  -> val + 2000); 
         h.compute("AWS", (key, val) 
                                      -> val - 3000); 
         // print new mapping  
         System.out.println("New Tutorial Price: " + h); 
     } 
 } 

Output:

Tutorial price: {Java=10000, Salesforce=8000, AWS=18000, Python=12000}
New Tutorial Price: {Java=12000, Salesforce=8000, AWS=15000, Python=12000} 

Example to illustrate the put() and get() method.

import Java.util.*; 
 class PutGetDemo { 
     public static void main(String[] args) 
     { 
         // Creating an empty Hashtable 
         Hashtable<Integer, String> h = new Hashtable<Integer, String>();
         // Inserting the values into table using put() method 
         h.put(1, "Java");  
         h.put(2, "Python"); 
         h.put(3, "Oracle"); 
         h.put(4, "Spring"); 
         h.put(5, "JDBC"); 
         // printing the Hashtable 
         System.out.println("Initial Table is: " + h);  
         // Getting the value at 4
         System.out.println("The Value at 4 is: " + h.get(4)); 
         // Getting the value at 1
         System.out.println("The Value at 1 is: " + h.get(1)); 
     } 
 } 

Output:

Initial Table is: {5=JDBC, 4=Spring, 3=Oracle, 2=Python, 1=Java}
The Value at 4 is: Spring
The Value at 1 is: Java 

Example to illustrate the containsValue() method.

import Java.util.*; 
 class ContainValueDemo { 
     public static void main(String[] args) 
     { 
         // Initializing an empty Hashtable 
         Hashtable<Integer, String> h = new Hashtable<Integer, String>(); 
         // adding values in the table 
         h.put(10, "Java");  
         h.put(15, "Pyhton"); 
         h.put(20, "Data Structure"); 
         h.put(25, "OS"); 
         h.put(30, "Andriod"); 
         // Displaying the Hashtable 
         System.out.println("Initial Table is: " + h);  
         // Checking for the Value 'Java' 
         System.out.println("Is the value 'Java' present? " + h.containsValue("Java")); 
         // Checking for the Value 'OS' 
         System.out.println("Is the value 'OS' present? " + h.containsValue("OS")); 
     } 
 } 

Output:

Initial Table is: {5=JDBC, 4=Spring, 3=Oracle, 2=Python, 1=Java}
The Value at 4 is: Spring
The Value at 1 is: Java 

Example to illustrate the containsKey() method

import Java.util.*; 
 public class ContainsKeyDemo { 
     public static void main(String[] args) 
     { 
         // Initializing an empty Hashtable 
         Hashtable<Integer, String> h =  new Hashtable<Integer, String>();
         // adding values into the table 
         h.put(1, "Java");  
         h.put(2, "Pyhton"); 
         h.put(3, "Data Structure"); 
         h.put(4, "OS"); 
         h.put(5, "Andriod"); 
         // printing the Hashtable 
         System.out.println("Initial Table is: " + h); 
         // Checking for the key_element '20'  
         System.out.println("Is the key '2' present? " +  h.containsKey(2));
         // Checking for the key_element '5' 
         System.out.println("Is the key '6' present? " + h.containsKey(6)); 
     } 
 } 

Output:

Initial Table is: {5=Andriod, 4=OS, 3=Data Structure, 2=Pyhton, 1=Java}
Is the key '2' present? true
Is the key '6' present? False 

Example to illustrating Enumeration keys() method

import Java.util.*; 
 class EnumKeyDemo { 
     public static void main(String[] arg) 
     { 
         // creating a hash table 
         Hashtable<Integer, String> h = new Hashtable<Integer, String>();       
         h.put(3, "Ankit"); 
         h.put(2, "Himanshu");  
         h.put(1, "Aakash"); 
         // create enumeration 
         Enumeration e1 = h.keys(); 
         System.out.println("keys are:"); 
         while (e1.hasMoreElements()) { 
             System.out.println(e1.nextElement()); 
         } 
     } 
 } 

Output:

keys are:
3
2
1 

Example to illustrating hashCode() method

import Java.util.*; 
 class HashCodeDemo { 
     public static void main(String[] arg) 
     { 
         // creating a hash table 
         Hashtable<Integer, String> h =  new Hashtable<Integer, String>(); 
         h.put(3, "Java"); 
         h.put(2, "Spring");  
         h.put(1, "Hibernate"); 
         // obtaining hash code 
         System.out.println("Hash code is: " + h.hashCode()); 
     } 
 } 

Output:

Hash code is: -709507933

Example to illustrating entrySet() method

import Java.util.*; 
 class EntrySetDemo { 
     public static void main(String[] arg) 
     { 
         // initializing a hash table 
         Hashtable<Integer, String> h =  
                new Hashtable<Integer, String>(); 
         h.put(3, "Ankit");  
         h.put(2, "Sumit"); 
         h.put(1, "Anubhav"); 
         // initializing set view for hash table 
         Set s = h.entrySet(); 
         // obtaining set entries 
         System.out.println("set entries: " + s); 
     } 
 } 

Output:

set entries: [3=Ankit, 2=Sumit, 1=Anubhav]



ADVERTISEMENT
ADVERTISEMENT