Ten minutes let you understand the Objective-C syntax (compared with Java and C ++)

Many programmers who want to develop IOS, or who are developing IOS, have done Java or C ++ before. The first time they see Objective-C code, they will have a headache, the syntax of Objective-C code is very different from that of Java and C ++. Some of them may feel like reading tianshu. However, the language is the same and has many commonalities. The following lists the comparison between the syntax of Objective-C and that of Java and C ++, so that you can easily understand the syntax of Objective-C.

First, let's see what is in the Objective-C header file and implementation file:

Header file:

Implementation file:

 

I. Comparison of functions
Helloworld Method
Java language:

Public void helloWorld (bool ishelloworld) {// What to Do}

C ++ language:

Void helloWorld (bool ishelloworld) {// What to Do}

Objective-C language:

-(Void) HelloWorld :( BOOL) ishelloworld {// What to Do}

The method with a minus sign (-) is an instance method. You must use an instance of the class to call this method. There is a plus sign, which indicates a static method of the class and can be called without instantiation.

2. Messages.
Message definition: send information to an object.
A message is a mechanism unique to the runtime environment of ios. It is similar to a class in C ++ or Java, or an instance call class or an instance method. What I'm talking about is similar. Their mechanisms are actually somewhat different.
Example:
[Object message]

[object  message:param1 withParameter:param2]NSString *string;  string = [[NSString alloc] initWithString:@"Hello"];  

The above code is similar:
Java/c ++: object. message ()
Java/c ++: object. message (param1, param2)
Java/c ++: string * str;
Str = new string ("Hello ");

Iii. Import
Example:
Import "Class. h"
Import <Class. h>
Import <director/Class. h>
This is similar to the include and java import in C ++.

Iv. Property and Synthesize
Property definition: @ property declaration is used to automatically create the getter and setter attributes of the property variable.
Synthesize definition: @ Synthesize declaration implements the getter and setter attributes of the property variable.
Example:
In interface: @ property dataType variableName
In implementation: synthesiz variableName

V. Methods in header files
Example: declare a method in the header file

-(returnType)method-(returnType)method:(dataType)param1-(returnType)method:(dataType)param1 withParam:(dataType)param2

Similar:
C/C ++/Java

returnType method()returnType method(param1)returnType method(param1,param2)

Vi. self
Pointing to your own pointer
[Self method] 

Similar to: c ++/java
This. method ();
VII. inheritance relationship and interface implementation
Example:

ClassA:ParentAClassA:ParentA<Protocol>ClassA <Protocol>

Similar:
Java:

ClassA extends ParentAClassA extends ParentA implements interfaceClassA implements interface

The Protocol of objective-c is similar to that of c ++ and java.

8. NULL pointer

Id obj = nil;
NSString * hello = nil;

Nil is equivalent to null in Java;

9. id
Objective-c is similar to void * in C ++.