object-c的動態識別與isKindOfClass,isMemberOfClass等

object-c提供了一批用於檢測一個對象是不是某個類的對象或成員，它們是isKindOfClass，isMemberOfClass，respondsToSelector，instancesRespondToSelector，performSelector等，
下面給出了這些函數的一些用法。

1.代碼：
// MyRectangle類和Square類略（它們的定義見前一節“8.object-c的繼承”），
// main.m
#import "Square.h"
#import "MyRectangle.h"
#import <stdio.h>

int main( int argc, const char *argv[] ) {
     MyRectangle *rec = [[ MyRectangle alloc] initWithWidth: 10 height: 20];
    Square *sq = [[Square alloc] initWithSize: 15];

    // isMemberOfClass

    // true 
    if ( [sq isMemberOfClass: [Square class]] == YES ) {
        printf( "square is a member of square class\n" );
    }

    // false
    if ( [sq isMemberOfClass: [ MyRectangle class]] == YES ) {
        printf( "square is a member of  MyRectangle class\n" );
    }

    // false
    if ( [sq isMemberOfClass: [NSObject class]] == YES ) {
        printf( "square is a member of object class\n" );
    }

    // isKindOfClass
    
    // true 
    if ( [sq isKindOfClass: [Square class]] == YES ) {
        printf( "square is a kind of square class\n" );
    }

    // true
    if ( [sq isKindOfClass: [ MyRectangle class]] == YES ) {
        printf( "square is a kind of  MyRectangle class\n" );
    }

    // true
    if ( [sq isKindOfClass: [NSObject class]] == YES ) {
        printf( "square is a kind of object class\n" );
    }

    // respondsToSelector

    // true
    if ( [sq respondsToSelector: @selector( setSize: )] == YES ) {
        printf( "square responds to setSize: method\n" );
    }

    // false
    if ( [sq respondsToSelector: @selector( nonExistant )] == YES ) {
        printf( "square responds to nonExistant method\n" );
    }

    // true
    if ( [Square respondsToSelector: @selector( alloc )] == YES ) {
        printf( "square class responds to alloc method\n" );
    }

    // instancesRespondToSelector

    // false
    if ( [ MyRectangle instancesRespondToSelector: @selector( setSize: )] == YES ) {
        printf( " MyRectangle instance responds to setSize: method\n" );
    }

    // true
    if ( [Square instancesRespondToSelector: @selector( setSize: )] == YES ) {
        printf( "square instance responds to setSize: method\n" );
    }

    // free memory
    [rec release];
    [sq release];
    
    return 0;
}

2. 運行結果：
$ ./main.exe
square is a member of square class
square is a kind of square class
square is a kind of  MyRectangle class
square is a kind of object class
square responds to setSize: method
square class responds to alloc method
square instance responds to setSize: method

3.說明：
  （1） 請和jave的instanceof相比較；
  （2） 請和java的 getClass相比較;
  （3） 所有繼承人自 NSObject 都有一個 class method。