First lecture, Class and Object-------(2)

First, the curriculum review

1. Object-oriented language

Object-Oriented Programming: focus on things

Process-oriented programming: event-centric

2. Classes and objects

Description class: Abstraction of something with the same characteristics and behavior

An object is an instance of a class, and a class is an abstraction of an object

3. Defining classes

Interface section: Declaring a class's characteristics (instance variables) and behavior (methods)

Implementation part: Implementation method

4. Create objects

Person * P1 = [[Person alloc] init];

Alloc class methods only classes can call

Function: Allocates storage space for the object in the heap area, empties the storage space, sets all instance variables to 0, and returns the first address of the object storage space.

Init instance methods only objects can be called

Role: set for instance variables

P1 essence: A pointer to the person type Object

When a pointer to an object type points to the created object, the P-generation is referred to as the object

5. Object Invocation Method

[P Sayhi];

Person * P2 = nil;

P2 cannot be referred to as an object, is a null pointer

In OC, any operation on nil is invalid.

Second, the instance variable operation

When you invoke an instance variable of the public adornment outside the class, which defines a part other than the class, use-

1. Assignment of instance variables

P->_name = @ "remote star Dream";

P->_age = 18;

2. Read the value of the instance variable

NSLog (@name =%@, age =%d ", p->_name, P->_age);

Output: name = Remote Star Dream, age = 18

3. Overriding Init initialization

1) Declaration Part-----Person.h

-(person *) init;

-(ID) init; -(Instancetype) init;----General wording

ID generic pointer type, can only point to object type

notation: ID Teacher * person * cannot represent int *

2) Implement part------PERSON.M

-(ID) init

{
_age = 18;

return self;

Self means that the method of initialization must return

}

4. Example method

1) Declaration part------Person.h

-(void) introduce;

2) Implement part------PERSON.M

-(void) introduce

{

NSLog (@ "My name is%@", _name);

All created person objects can call instance methods that belong to this object

instance method, you can use the instance object directly

Which object invokes the instance method, the value in the instance variable is the value of the current object

}

3) Call-------MAIN.M

[P introduce];

Output: My name is the dream of a distant star

This article is from the OC Learning Notes blog, so be sure to keep this source http://10613955.blog.51cto.com/10603955/1684482

First lecture, Class and Object-------(2)