Java SE: Programming Complete - 5

https://learn.oracle.com/ols/course/java-se-programming-complete/82508/85200

Improved Class Design

Use Method Overloading

• Two or more methods, with the same class, that have identical names.
• Must have a different number, or different types, or different order of parameters, return type doesn’t count, compile error.
• To make it easier for caller to make the call.

Variable Number of Arguments

• The vararg feature enables a variable number of arguments of the same types
• The vararg parameter is treated as an array, with the length constant indicating a number of values.
• In case where there are other parameters in the method, the vararg parameter must be defined last.

class example {
  public static void main(String[] args) {}
  // Or
  // public static void main(String... args) {}
}

Define Constructors

• Same name as the class name, no return type.
• A default constructor with no parameters is implicitly added to the class, only if no other constructors were added
• A constructor can invoke another to reuse its logic, by using keyword this(other constructor parameters);, and it must be the first line of code in the nvoking constructor.
• A cycle of constructor invocations is not allowed.

Access Modifiers

• public - visible to any class
• protected - visible to subclasses and class in same package
• - visible to class in smae package
• private - visible within the same class only

Define Encapsulation

• Information contained within the object should normally be “hidden” inside it.
• Use access modifiers properly to control access

Define Immutability

• Immutability objects present read-only data.
• Instance variables must be encapsulated (private) to prevent direct access.
• Instance variables are initialized immediately or via constructors (use final or not).
• No setter mothods, only getter.
• Benifit, immutable objects are thread-safe, without an overhead cost of coordinating synchronized access.
• Instance initializer (compare static initializer, no static keyword) is triggered before the invocation of the constructor, can initialize final instance variable.

Enumerations

• Enumeration (enum) provides a fixed set of instances of a specific type
• Enum values are instances of this enum type.
• Enum values are implicitly public static final
• Enum can define instance variables and methods.
• A constructor should be added to the enumeration to initialized its instance variables.
• The constructor for an enum must have default or private access
• Declaration of enum values invokes the enum constructor.
• The enum constructor can be invoked outside of enum.

Java Memory

• Stack is a memory context of a thread, storing local method variable: primitives or object reference
• Heap is shared memory, accessible from different method and thread contexts.
• parameter passing means copying stack values.
• Garbage collection will clean object when there are no reference pointing to it