The difference between abstract and general code

Question

What is the difference between the word "abstract" and the "common" code in the case of Java? Are both the same?

Answer 1

Abstract and generics are completely different things in the syntax and semantics of Java.

abstract is a keyword and indicates that the class does not contain a full implementation, therefore it cannot be created.

Example:

abstract class MyClass {
  public abstract void myMethod();
}

MyClass contains a definition of the public public void myMethod () 'method, but does not specify an implementation - the implementation should be provided by a subclass, usually called a specific subclass, so an abstract class defines an interface, possibly with some implementation details.

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Answer 2

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public abstract class Animal{
   protected int calories;

   public void feed(int calories){
      weight += calories;
   }

   public abstract void move(); // All animals move, but all do not move the same way
                                // So, put the move implementation in the sub-class
}

public class Cow extends Animal{
    public void move(){
       // Some code to make the cow move ...
    }
}

public class Application{
   public static void main(String [] args){
      //Animal animal = new Animal()   <- this is not allowed
       Animal cow = new Cow() // This is ok.
   }
}

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Generic Generics Java, , - . ArrayList, , , , ArrayList, ( ArrayList, ints). Generics Java, , ints ArrayList ( String ArrayList).

public class Application{
   public static void main(String [] args){
      ArrayList noGenerics = new ArrayList();
      ArrayList<Integer> generics = new ArrayList<Integer>();

      nogenerics.add(1);
      nogenerics.add("Hello"); // not what we want, but no error is thrown.

      generics.add(1);
      generics.add("Hello"); // error thrown in this case

      int total;
      for(int num : nogenerics)  
          total += num;
      // We will get a run time error in the for loop when we come to the
      // String, this run time error is avoided with generics.
   }
}

Answer 3

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Answer 4

Annotation is used to determine what requires an additional definition of functionality before it is considered "complete" (or specific in Java-certification-test-terms). Generic means a class that can handle a wide variety of data types that you define when you instantiate the class.