Java Tutorial

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Java Loops

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Java Programs

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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 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


Java Serialization Java transient


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


Java AWT


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 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


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

Aggregation in Java

An aggregation is a special form of association. Aggregation is used when we need to use property and behavior of a class without modifying it in the class. Aggregation is also used to achieve code reusability.

  • We have two types of relationships one is HAS A and other is IS A relationship and Aggregation represents IS A relationship.
  • It is a special form of association i.e. unidirectional association. To understand it, let's take an example: There is an officer and a no. of employees are working for him. Then we can say Officer ‘HAS A ‘employee working for him but vice versa is not true.
  • In aggregation both the entity survive individually. If we end one entity that doesn't affect the other entity.
import java.util.*;
// employee class
class Employee
String name;
int id ;
String oname;// officer name under whom he work
Employee(String name, int id, String oname)
{ = name; = id;
this.oname = oname;
/* Officer Class contains list of employee
Objects. It is associated with Employee
Class through its Object(s). */
class Officer
String name;
private List< Employee> employees;
Officer (String name, List<Employee> employees)
{ = name;
this.employees = employees;
public List<Employee> getemployees()
return employees;

/* Company class contains list of Employee
Objects. It is associated with Officer
Class through its Object(s).*/

class Company
String cName;
private List<Officer> officers;
Company (String cName, List<Officer> officer)
this.cName = cName;
this.officers = officer;
// count total employees of all officers
// in a given company
public int getTotalEmployeesInCompany()
int noOfEmployees = 0;
List<Employee> employees;
for(Officer oname : officers)
employees = oname.getemployees();
for(Employee e : employees)
return noOfEmployees;
// main method
class Main
public static void main (String[] args)
Employee e1 = new Employee("Mia", 1, "Sachin sir ");
Employee e2 = new Employee(" Mira", 2, "Sachin sir ");
Employee e3 = new Employee("Mahesh ", 3, "Ashish sir ");
Employee e4 = new Employee("Manish ", 4, " Ashish sir ");
// making a List of
// Sachin sir Employees.
List <Employee> Sachinsir_employee = new ArrayList<Employee>();
Sachinsir_employee.add (e1);
Sachinsir_employee.add (e2);
// making a List of
// AshishsirEmployees
List <Employee> Ashishsir_employee = new ArrayList<Employee>();
Ashishsir_employee.add (e3);
Ashishsir_employee.add (e4);
Officer o1= new Officer ("Sachinsir", Sachinsir_employee);
Officer o2 = new Officer ("Ashishsir", Ashishsir_employee);
List <Officer > officers = new ArrayList<Officer>();
// creating an instance of Company.
Company company= new Company("ABC", officers);
System.out.println("Total employees in company: ");
Total employees in company: 

Example explanation:

In this example, there is a company let's say ABC which has no. of officers like Sachin sir, Ashish sir. Every officer has no. of employees working for him. So, we make a company class which has a reference to Object or no. of Objects (i.e. List of Objects) of the Officer class. That means Company class is associated with Officer class through its Object(s). And Officer class has also a reference to Object or Objects (i.e. List of Objects) of Employee class means it is associated with Employee class through its Object(s).

Let's see diagrammatically what happened in this example: