Java Object-oriented (base) Knowledge Point summary I__java

1, class and object difference, class is an object template, object is a class instance

2, create the syntax of the class class name {}, the class is composed of properties and methods

3, the creation of the syntax of the object:

·     Declaring object: Class Name Object name = NULL; Equivalent to declaring an object name in the stack memory space, which is actually the address of the saved heap

• Instantiate object: Object name = new class name (); To open up the heap of memory space, the heap is stored in all the attributes

· The reference passing between classes actually conveys the right to use the heap memory space

· If an object is declared but not instantiated, a null-pointing exception appears when used

· Garbage object generation: Useless memory space, no stack memory pointing, and a stack memory can only point to a heap memory space

4, Encapsulation: The contents of the class is not visible to the outside

· The Private keyword can now be used to implement encapsulation in Java, but the encapsulated attributes can only be set and obtained by the setter and Getter methods

· In the design of a class, all attributes are required to be encapsulated. This is a standard design principle.

5. Construction method

· A construction method exists in any class

· Construction method name is consistent with class name, no return value type

· The construction method is invoked automatically when the object is instantiated using the keyword new

· If there is no explicit declaration of a constructor in a class, a parameterless constructor is automatically generated

6. String class

· String can be instantiated in two ways:

|-Direct assignment: It will only open up a heap of memory space

|-New Stirng (): will open two heap memory space, there is a garbage

· Once the contents of a string are declared immutable, the change is only to the point where the memory address

· A string is an anonymous object of a string

· Several action methods are provided in the String class: substring (), ReplaceAll (), Split (), Length ()

7. This keyword

· Use this to represent the current object, the object that is currently manipulating the method

· Use this to invoke a property or method in a class

· Use this to call the constructor method, but it must be placed in the first row of the construction method

The two purposes of this keyword: ① refers to implicit arguments, and ② calls other constructors of that class.

8, Super keyword

Two uses: one is to call the superclass method, and the other is to call the superclass constructor.

This, super keyword is used in a similar way when calling a constructor. Can only appear as the first statement of another constructor

9, a class can receive its own reference to this class but this usage is only used in the object comparison one position