Java's three major object-oriented features: 1. Encapsulation, which aims to enhance data security and simplify programming; 2. Inheritance, which refers to extracting multiple identical properties and methods and creating a new parent class , the purpose is code reuse; 3. Polymorphism, the purpose is to increase the flexibility of the code.
The operating environment of this tutorial: windows7 system, java8 version, DELL G3 computer.
1. Encapsulation
Encapsulation It refers to the privatization of properties
Purpose: Enhance data security, prevent other users from accessing and modifying data at will, simplify programming, users do not need to care about specific implementation details, but just pass The external interface can access the members of the class
2. Inheritance (Extend)
Inheritance refers to extracting multiple identical properties and methods Come out and create a new parent class
Purpose: Code reuse
3. Polymorphism
Polymorphism (Polymiorph) can be divided into two types: design-time polymorphism and run-time polymorphism
Design (compile)-time polymorphism: Overload , means that Java allows the same method name but different parameters (the return value can be the same or different). One or more functions with the same name are allowed to exist in the same class, as long as the parameter type or number of parameters are different
Runtime polymorphism: That is, override must be in the inheritance system. The subclass overrides the parent class method. The JVM runtime determines which method to call based on the type of the method being called.
Purpose: Increase the flexibility of the code
<span style="font-size: 18px;">Summary:</span>
1. Inheritance should be minimized in java relationship to reduce coupling
2. When using polymorphism, when the parent class calls a method, it will first call the method of the subclass. If the subclass does not override the method of the parent class, then the method of the parent class will be called. Method
3. Java access control character scope table:
This class Package | Subclass | External package | ||
---|---|---|---|---|
✓ | ✓ | ✓ | ✓ | |
✓ | ✓ | ✓ | X | |
✓ | ✓ | X | X | |
✓ | X | X | X |
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