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public abstract class Optional<T> {

    public static <T> Optional<T> of(T value) {
        return value != null ? new Present<T>(value) : Absent.<T>instance();
    }

    public <V> Optional<V> flatMap(Function<T, Optional<V>> function) {
        return isPresent() ? function.apply(get()) : Absent.<V>instance();
    }

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public class MapVsFlatMap {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3);

        //Stream<X> --map (square)--> Stream<X>
        list.stream()
                .map(it -> it * 2)
                .forEach(it -> System.out.println(it));

        // Stream<X> --map--> Stream<Optional<X>> --filter--> Stream<Optional<X>> --each--> Print

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object Currying {

   def sum(f: Int => Int) : (Int, Int) => Int = {
     def sumF(a: Int, b: Int) : Int = {
       if(a > b) 0
       else f(a) + sumF(a + 1, b)
     }

     sumF
   }

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/*
 * This is a mockup of JLine2 library structure. I am working on a feature that provides timestamp
 * and wanted to test it and hence this gist. The question that I asking via this gist is that how
 * should I test MemoryHistory?  
 */


/**
 * Represents the history of commands a user has given to a system via any interface such as
 * Command Line

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keytool -importkeystore -srckeystore middleware_keystore_org -destkeystore private_key.p12 -deststoretype PKCS12
openssl pkcs12 -in private_key.p12 -out private_key.pem -nodes
openssl pkcs12 -export -inkey private_key.pem -in Meydan1-certnew_941.cer -name test -out test.p12
keytool -importkeystore -srckeystore test.p12 -srcstoretype pkcs12 -destkeystore middleware_keystore_try3.jks
keytool -list -v -keystore middleware_keystore_try3.jks

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I don't have much time and I have to change it

Sprout Method

If a change is too difficult to make in existing method, then create a new method which performs additional work and call it from existing method. Unit test the new method, even if it requires to make it static and pass all dependencies in it.

Sprout Class

Similar to sprout method, but if creating instance of class is too difficult to do in limited time, or maybe it will require separating a lot of dependencies. Create another class to hold changes and use from original difficult to test class. Unit test sprouted class properly. This may seem like making the code worse, and sometimes is, but many times it helps in figuring out commanality between sprouted class and some new class in future and improves chances of carving out interfaces or resusable classes.

Wrap method

If new functionality is cleanly separable, then rather than adding more stuff to existing method, we can make original method as private and rename it to give apt

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Why Zookeeper

• Coordination services are notoriously hard to get right.
• Race conditions and deadlock.

The motivation behind ZooKeeper is to relieve distributed applications the responsibility of implementing coordination services from scratch.

Zookeeper

• Distributed co-ordination service
• eases the development of distributed systems

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Ubiqutous language

In DDD it really important that everyone business people and developers share a model. A model is shared understanding of the system. It helps in forming a common language between all the stakeholders. This makes sure that the code design doesn't drift from the model and it reflects the domain.

Model

The model has to be tightly associated with the domain it comes from. Designing without a model can lead to software which is not true to the domain it serves, and may not have the expected behavior.

One of the first things we are taught about modeling is to read the business specifications and look for nouns and verbs. The nouns are converted to classes, while the verbs become methods. This is a simplification, and will lead to a shallow model. All models are lacking depth in the beginning, but we should refactor the model toward deeper and deeper insight.