Teachnique
      CourseRoadmaps
      Login

      OverviewHistoryFeaturesJava 8 - New Featuresvs C++Virtual Machine(JVM)JDK vs JRE vs JVMHello World ProgramEnvironment SetupBasic SyntaxVariable TypesData TypesType CastingUnicode SystemBasic OperatorsCommentsStreamsNew Date-Time API

      Loop ControlDecision Makingif-else Statementswitch statementfor loopfor each Loopwhile Loopdo...while Loopbreak Statementcontinue Statement

      OOPs (Object-Oriented Programming) ConceptsObject and ClassesClass AttributesClass MethodsMethodsVariable ScopesConstructorsAccess ModifiersInheritanceAggregationPolymorphismOverridingMethod OverloadingDynamic BindingStatic BindingInstance Initializer BlockAbstractionEncapsulationInterfacesPackagesInner classesStatic ClassesAnonymous ClassesSingleton ClassWrapper ClassesEnum Class

      Number ClassBoolean classCharacter ClassArraysMath Class

      File ClassCreating FilesWrite To FilesReading FileDelete FilesDirectory OperationsFiles and I/O

      ExceptionsTry Catch BlockTry with ResourcesMultiple Catch BlocksNested Try BlockFinally BlockThrows and Throw | Throw an ExceptionException PropagationBuilt-in ExceptionsCustom Exception

      MultithreadingThread Life CycleCreating a ThreadStarting a ThreadJoining ThreadsNaming a Thread with ExamplesScheduling Threads with ExamplesThread PoolsMain ThreadThread PriorityDaemon ThreadThreadGroup ClassJVM Shutdown Hook

      Thread SynchronizationBlock SynchronizationStatic SynchronizationInter Thread CommunicationThread DeadlockInterrupting ThreadThread ControlReentrant Monitor

      NetworkingSocket ProgrammingURL ProcessingURL ClassURLConnection ClassHttpURLConnection ClassSocket Class with ExamplesGenerics

      Collections FrameworkCollection Interface

      List InterfaceArrayList Class

      Queue InterfaceArrayDeque Class

      Map InterfaceSortedMap Interface

      Set InterfaceSortedSet Interface

      Data Structures Enumeration Interface BitSet Class

      How to Use Iterator?How to Use Comparator?How to Use Comparable?

      RecursionRegular ExpressionsSerializationString ClassJava Arrays - Class

      Feedback

      Submit request if you have any questions.

      Course
      Aggregation

      Java Tutorial

      This Java tutorial is tailored for newcomers, offering a journey from basic principles to complex Java programming techniques. Completing this tutorial equips you with a solid understanding of Java, preparing you for advanced learning. You'll emerge ready to tackle the challenges of becoming a top-tier software engineer, with the skills to innovate and excel in the vast world of software development.

      Aggregation

      Java Aggregation

      An aggregation is a relationship between two classes where one class contains an instance of another class. For example, when an object A contains a reference to another object B or we can say Object A has a HAS-A relationship with Object B, then it is termed as Aggregation in Java Programming.

      Use of Java Aggregation

      Aggregation in Java helps in reusing the code. Object B can have utility methods and which can be utilized by multiple objects. Whichever class has object B then it can utilize its methods.

      Java Aggregation Examples

      Example 1

      In this example, we're creating few classes like Vehicle, Speed. A Van class is defined which extends Vehicle class and has a Speed class object. Van class inherits properties from Vehicle class and Speed being its property, we're passing it from caller object. In output, we're printing the details of Van object.
      package com.tutorialspoint;
      
      class Vehicle{
         private String vin;
      
         public String getVin() {
            return vin;
         }
      
         public void setVin(String vin) {
            this.vin = vin;
         }	
      }
      class Speed{
         private double max;
      
         public double getMax() {
            return max;
         }
      
         public void setMax(double max) {
            this.max = max;
         }
      }
      
      class Van extends Vehicle {
         private Speed speed;
      
         public Speed getSpeed() {
            return speed;
         }
      
         public void setSpeed(Speed speed) {
            this.speed = speed;
         }
      
         public void print() {
            System.out.println("Vin: " +this.getVin() + ", Max Speed: " + speed.getMax() );
         }
      } 
      
      public class Tester {
      
         public static void main(String[] args) {
            Speed speed = new Speed();
            speed.setMax(120);
            Van van = new Van();
      
            van.setVin("abcd1233");
            van.setSpeed(speed);
            van.print();
         }
      }

      Output

      Vin: abcd1233, Max Speed: 120.0

      Example 2

      In this example, we're creating few classes like Student, Address. A student can has a address. So we've defined an address as an instance variable in Student class. In output, we're printing the student details.
      package com.tutorialspoint;
      
      class Address {
         int strNum;
         String city;
         String state;
         String country;
      
         Address(int street, String c, String st, String country) {
            this.strNum = street;
            this.city = c;
            this.state = st;
            this.country = country;
         }
      }
      class Student {
         int rno;
         String stName;
      
         Address stAddr;
         Student(int roll, String name, Address address){
            this.rno = roll;
            this.stName = name;
            this.stAddr = address;
         }
      }
      
      public class Tester {
      
         public static void main(String[] args) {
            Address ad= new Address(10, "Bareilly", "UP", "India");
            Student st= new Student(1, "Aashi", ad);
            System.out.println("Roll no: "+ st.rno);
            System.out.println("Name: "+ st.stName);
            System.out.println("Street: "+ st.stAddr.strNum);
            System.out.println("City: "+ st.stAddr.city);
            System.out.println("State: "+ st.stAddr.state);
            System.out.println("Country: "+ st.stAddr.country);
         }
      }

      Output

      Roll no: 1
      Name: Aashi
      Street: 10
      City: Bareilly
      State: UP
      Country: India
      In a unique sense, this is a type of association. Aggregation is a one way directed relationship that precisely expresses HAS-A relationship between classes. Additionally, when two classes are aggregated, terminating one of them has no effect on the other. When compared to composition, it is frequently designated as a weak relationship. In comparison, the parent owns the child entity, which means the child entity cannot be accessed directly and cannot exist without the parent object. Contrarily, in an association, the parent and child entities may both exist in their own right.

      HAS-A Relationship

      These relationships are mainly based on the usage. This determines whether a certain class HAS-A certain thing. This relationship helps to reduce duplication of code as well as bugs.

      Example

      public class Vehicle{}
      public class Speed{}
      
      public class Van extends Vehicle {
         private Speed sp;
      }
      This shows that class Van HAS-A Speed. By having a separate class for Speed, we do not have to put the entire code that belongs to speed inside the Van class, which makes it possible to reuse the Speed class in multiple applications.
      In Object-Oriented feature, the users do not need to bother about which object is doing the real work. To achieve this, the Van class hides the implementation details from the users of the Van class. So, basically what happens is the users would ask the Van class to do a certain action and the Van class will either do the work by itself or ask another class to perform the action.
      
      
      
      
      Print Pag