Thinking in Java Reading Notes -- 1. introducation to object

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Thinking in Java

• 1. introducation to object
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    object-oriented -- abstraction
    • 1. You can regard all the conceptual components of the problem to be solved as an object.
    • 2. Program is a group of objects that send messages to each other and tell the other party what to do.
      A message is a request that calls a method specific to an object.
    • 3.
    • 4. Any object is an instance of a class
    • 5. All objects belonging to the same class can accept the same message
    • all objects have statuses, behaviors, and labels
    • each object belongs to a class, and these classes define its features and behaviors
    • A Class describes a group of objects with common features and behaviors.
    • A class is actually a data type.
      • class, customized by programmers to solve specific problems
      • data type, designed to represent a computer's storage unit
    • object, which is an instance of the class
    • each object is an independent entity of this class
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    object-oriented -- interface
    • each object can only meet certain requests, and the object can accept requests.
      it is determined by the interface defined by its class.
    • the interface is only responsible for determining the requests that the object can accept, and the response of the object to the
      request, implemented by Code
    • you send a message (submit a request) to the object
      the object determines how to handle the message (execute code)
    • light lT = new light ()
      lt. On ();
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    object-oriented -- service
    • Object-service provider
      the task of a software engineer is to create a group of objects that provide the best service to solve the problem.
    • in a good object-oriented design, an object should only do
      one thing, and do one thing well, instead of doing many things.
    • good object-oriented design should be highly cohesive
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    hide
    • programmer classification
      • creator of the class
      • customer programmer-class user
    • hiding the internal implementation of the class can avoid misoperation of sensitive parts inside the class.
    • only allow client programmers to access the service through class-defined interfaces.
      it can be used without affecting client programmers, modify the specific internal implementation
    • Public -- accessible to anyone
    • private -- only the class creator can access
    • protected -- only the inherited class can be accessed
    • package -- default access permission
      • members with default access permissions of other classes that belong to the same package
      • outside the package, members with default access permissions are treated as private members.
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    reuse implementation
    • directly create an object with a class
    • place the class object in a new class -- create a member object
    • synthesize composition -- combine multiple existing classes of different types into new classes
    • aggregate aggregation-Dynamic Synthesis
    • generally, "merging" is a has-a relationship. For example, a car has an engine.
    • when creating a new class, the use of "synthesis" should be given priority
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    inheritance: Reuse interface
    • base class, superclass, parent class
    • derived class, inherited class, subclass
    • changes in the base class affect the derived class
    • the base class stores the common features and behaviors of all classes inherited from it.
    • all messages that can be passed to the base class can also be passed to Their Derived classes
    • you can determine what type of message a class can receive.
    • the derived class and the base class belong to the same type-class equality
    • extends
    • override -- Method for redefining the base class in the derived class
    • completely replace (pure substitution)
    • is-a relationship
    • is-like-a relationship
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    Polymorphism
    • Generic
    • Bind later
    • Upcasting
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    Abstract
    • The compiler prohibits anyone from creating abstract objects.
    • Abstract Method
    • The abstract method only exists in the abstract class.
    • Abstract method indicates that all classes derived from this class have this method,
      
      But the implementation of this method is not here
    • If a class inherits from the abstract class
      
      Method implementation is either an abstract class
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    Interface keyword
    • It is not allowed to implement any method to completely separate interfaces from implementations.
    • It can inherit multiple interfaces, but cannot inherit multiple common classes or abstract classes.
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    Object Creation
    • Create -- C ++ In the heap
    • Create Java in stack
    • New Keyword
    • Garbage Collector
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    Container)
    • Iterator
  • Single Inheritance System
  • Upload/download/parameterized type
  • Exception Handling
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    Concurrency
    • Thread
    • Lock Resources
  • Persistence
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    Java and Internet
    • Web
    • Client Programming
    • Plug-ins
    • Script Language
    • Server programming
      • Servlet
      • JSP
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    Why is Java successful?
    • The system is easier to express and understand
    • Maximize the use of Class Libraries
    • Exception Handling
    • Suitable for compiling large systems
  • Java or C ++?