The WeakReference class, monitoring memory leak and garbage collection in a Java application

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Image
 Below is a Stack implementation that uses an internal resizeable array structure.  public class MyStack< T > implements Stack< T > { private static final int CAPACITY = 100 ; private Object[] array ; private int pos = 0 ; public MyStack () { this . array = new Object[ CAPACITY ] ; } @Override public void push ( T item) { if ( pos >= array . length / 2 ) { Object[] newArray = new Object[ pos * 2 ] ; System. arraycopy ( array , 0 , newArray , 0 , array . length ) ; array = newArray ; } array [ pos ++] = item ; } @Override public T pop () { if (isEmpty()) { throw new RuntimeException( "empty stack" ) ; } @SuppressWarnings ( "unchecked" ) T item = ( T ) array [ pos - 1 ] ; pos -= 1 ; return item ; } @Override @SuppressWarnings ( "unchecked" ) public T peek...
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Revisiting the Axon Framework

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Axon is a CQRS Framework for scalable and high-performance applications. Lets look at the evolution of the API from Axon 1 to Axon 3:


With Axon 3, Aggregate  interface is introduced and we pass the method to the execute() method:

Axon 1:

@CommandHandler
public void handle(final ChangeClientNameCommand command, UnitOfWork unitOfWork) {

    Client client = clientRepository.load(new StringAggregateIdentifier(command.getClientIdentifier()));

    client.changeNameAs(command.getNewName());
}


Axon 3:

@CommandHandler
public void handle(final ChangeClientNameCommand command) {

    Aggregate client = clientRepository.load(command.getClientIdentifier().toString());

    client.execute(aggregateRoot -> aggregateRoot.changeNameAs(command.getNewName()));
}





In the past Client entity was derived from a class called "AbstractAnnotatedAggregateRoot". Now in Axon 3, it is just a POJO and the Repository does not return a Client entity but an "aggregate". We pass the function as a parameter. At the time of Axon 1.0, Java language did not have support for lambda expressions.







Axon 1:









public class Client extends AbstractAnnotatedAggregateRoot {



    private String name;



    private Address address;



    private String phoneNumber;









Axon 3:








@AggregateRootpublic class Client {

    @AggregateIdentifier    private ClientId companyId;

    private String name;
    private Address address;
    private String phoneNumber;





Domain entities are not dependent to a base class anymore. We see this pattern in many frameworks like Unit Test frameworks. There is even a project called Lombok that uses annotations for simpler code.







To be continued..




















































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