Object-oriented syntax-02

• Next, simulate real-life situations in OC and create a car. First you have to have a car class, and then use the car class to create a car object

1. Classes that define OC and objects that create OC

• To describe a class in OC is a little cumbersome, in 2 steps: The declaration of the class, the implementation of the class (definition). Similar to functions, functions have a sub-declaration and definition

1. Declaration of the class

1. Code writing

• Define a car class with 2 properties: Number of wheels, speed, 1 behaviors: Running
• Naming rules for class names \ Properties: Rules for identifiers
• Naming conventions for class names: Meaningful, hump-marked, first-letter capitalization

Declaration of #import <Foundation/Foundation.h>// class @interface  car:nsobject{     @public    int // How many wheels?    int // Speed }-(void//  run behavior @end

1. Member variables

• Variables declared in @interface curly braces {}: Wheels, Speed
• @interface curly braces and curly braces for functions are not the same
• Default is initialized to 0

1. @public

@public allows the wheels and speed properties of the car object to be accessed by the outside world

1. NSObject

Plus: The purpose of NSObject is to have the car class capable of creating objects

1. class the implementation

// implementation of the class @implementation car-(void) run{    NSLog (@ "%i wheels,%i the speed of the car ran up. " , wheels, Speed);} @end

1. Creating objects

1. Code writing

// Main function int Main () {    //  Create car object      new];    C3;    C;        [C Run];     return 0 ;}

1. Code analysis, memory analysis for the main function (objects have members in memory)

• [Car New] Creates a new object each time, and returns the address of the object, then the address of the object should be saved with a pointer variable

New];

Use a pointer variable C to point to the in-Memory car object

• Set the properties of a car object

As with pointers to structs, access struct properties,

3 ; c ;

1. Create multiple Car objects

• Set only wheels, speed properties, respectively

New ];c14new];c2; [ C1 run];

• 1 assign to another, and then modify the property

New ];c14; C1*c2 = c1;c23; [ C1 run];

1. The benefits of object-oriented encapsulation

• Closer to the way people think
• Just focus on the object and don't need to follow the steps

1. object and Function parameters

• Object member variables as function arguments
• Pointer to object as function parameter

• To modify a pointer to a member of an object
• To modify the pointer's pointing

1. Declaration and implementation of a class

1. @interface and the @implementation Division of Labor

• @interface's like exposing the outside clock surface
• @implementation is like a structure hidden inside the clock.

1. Declaring and defining multiple classes

1. Common errors

• Only the declaration of the class, no implementation of the class
• Missed the @end.
• @interface and @implementation nesting
• Declaration nesting of two classes
• Member variables are not written in parentheses
• The declaration of the method is written in curly braces.

1. Syntax details

• Member variables cannot be initialized in {} and cannot be accessed directly
• Method cannot be called as a function
• member variable \ Method cannot be decorated with keywords such as static, do not mix with C language (temporarily ignore)
• The implementation of the class can be written after the main function, mainly after the declaration.

1. The difference between OC methods and functions

• The OC method can only be declared between @interface and @end and can only be implemented between @implementation and @end. This means that the OC method cannot exist independently of the class
• C functions do not belong to the class, and the class is not associated with the C function only to define the function of the file all
• C functions cannot access members of OC objects
• Low-level Error: The method has a declaration, but the implementation of the time is written as a function

1. OC the method of attention

• Method only declared, not implemented (classic error)
• method is not declared, only implemented (compiler warning, but can invoke, OC's weak syntax)
• Compile time: Access no member variable directly error, Access no method, just warning

1. @ Implementation

• There is no @interface, only @implementation, is also able to successfully define a class of

@implementation car:nsobject{    @public    int//  number of wheels    int//  speed }-(void) run{    NSLog (@ "%i wheels,% I ran at the speed of the car ", Wheels; @end

• The same member variable cannot be declared in the @implementation as @interface

1. Method

Design a Caculator calculator class, which has the function of calculation (behavior)

1. Methods with no parameters

• Design a method to return pi

// Method declaration -(double) pi; // method Implementation -(double) pi{    return3.14;}

• Method invocation

1. Method with one parameter

• Design a method for calculating squares

// Method declaration -(double) square: (double) number; // method Implementation -(double) square: (double) number{    return number *  number;}

• Method invocation

1. A method with multiple parameters

• Design a method of calculation and

// Method declaration -(double) sumOfNum1: (Double) num1 andNum2: (double)num2; // method Implementation -(double) sumOfNum1: (double) num1 andNum2: (Double)num2{     return num1 + num2;}

• Method invocation

1. Method Name Note

• The colon is also part of the method name
• Two object methods with the same name are not allowed in the same class

1. Exercises

Car class design a method to compare the speed with other cars, if the car speed, return 1, if the car is slow, return 1, the same speed return 0

1. Anonymous objects

• Property access

  [Car  New ;

• Method invocation

[[Car  New]  run];

Object-oriented syntax-02