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Java misc (Optional (Never assign null to an optional variable, initialize…

- - - - Doubles store values as binary and therefore might introduce an error solely by converting a decimal number to a binary number, without even doing any arithmetic.
      - Base 10 instead of Base 2, a BigDecimal is n*10^scale where n is an arbitrary large signed integer and scale can be thought of as the number of digits to move the decimal point left or right
- - - - Why can’t you make access modifier more restrictive (e.g. public to private)?
        It’s a fundamental principle in OOP: the child class is a fully-fledged instance of the parent class, and must therefore have at least the same interface as the parent class. Making less visible would violate this idea; you could make child classes unusable as instances of the parent class.
  - - - Why can’t you override static methods?
        Because static methods are related to class not to state of object so You can declare static method in child class but it has nothing to do with parent class. It is method hiding not overriding.
    - - A private method cannot be overridden since it is not visible from any other class. You can declare a new method for your subclass that has no relation to the superclass method. So it is not method overriding.
- - - - Pass-by-Reference
        
        When a parameter is pass-by-reference, the caller and the callee operate on the same object.
      - pass-by-value
        
        When a parameter is pass-by-value, the caller and the callee method operate on two different variables which are copies of each other. Any changes to one variable don't modify the other.
    - - Arguments in Java are always passed-by-value. During method invocation, a copy of each argument, whether its a value or reference, is created in stack memory which is then passed to the method.
      - Primitive variables store the actual values, whereas Non-Primitives store the reference variables which point to the addresses of the objects they're referring to. Both values and references are stored in the stack memory.
      - A Java object, in contrast to Primitives, is stored in two stages. The reference variables are stored in stack memory and the object that they're referring to, are stored in a Heap memory.When we pass an object, the reference in stack memory is copied and the new reference is passed to the method. However, if we allocate a new object to the passed reference variable, then it won't be reflected in the original object.
      - As a result of this, whenever we make any change in the same object in the method, that change is reflected in the original object.