[Java筆記] Object Oriented

• 使用 Annotation "@Override" 標示是個 overriding method,
  若 superclass 不包含同 signature 的 method, 會出現compiler error.

• Defining a Method with the Same Signature as a Superclass's Method
  

  	Superclass Instance Method	Superclass Static Method
  Subclass Instance Method	Overrides	Generates a compile-time error
  Subclass Static Method	Generates a compile-time error	Hides

• Overriding:
  不允許 throw new checked exception,
  但 unchecked exception 可以 (e.g. RuntimeException).
• Covariant return type:
  the return type of the overriding method is
  a subtype of the return type of the overridden method.
• e.g.
  class AA
  class A extends AA
  class B extends A
  class C extends B
  
  class superTest{
      public A method1(){
          return new A();
      }
  }
  
  class subTest extends superTest{
      public B method1(){ // or public C method1()
          return new C();
      }
  }

• Method inner class
• e.g.
  void method1(){
      class A {
          // some implement.
      }
  }
•  Singleton Pattern
• Constructor 設為 private
• Method getInstance() 設為 static 及 synchornized
• Override method clone()
• Cohesion: the whole of a class sticks together.
  Coupling: the inter dependency between 2 or more classes.
• Ideally design: high cohesion and loose coupling.

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