呼出同一個方法，根據呼出方不同執行的處理也不同

//---------------------------------------------------------------------
//                           類型定義
//---------------------------------------------------------------------
//動態結合與多態
@interface S4_A : NSObject {
    
}
- (void)getLocationOfHierarchy;
 
- (void)getLocationOfHierarchy:(BOOL)isneedHello;
@end

@interface S4_B : S4_A {
    
}
- (void)getLocationOfHierarchy; //重載
- (void)getLocationOfHierarchy:(BOOL)isneedHello; //重載
@end


//---------------------------------------------------------------------
//                          類定義
//---------------------------------------------------------------------
 
//動態結合與多態
@implementation S4_A
- (void)getLocationOfHierarchy {
    puts("this is A");
}
- (void)getLocationOfHierarchy:(BOOL)isneedHello {
    if (isneedHello) {
        puts("hello, this is A");
    } else {
        puts("need no hello, this is A");
    }
    
}
@end

@implementation S4_B
- (void)getLocationOfHierarchy {
    puts(
 
"this is B");
}
- (void)getLocationOfHierarchy:(BOOL)isneedHello {
    if (isneedHello) {
        puts("hello, this is B");
    } else {
        puts("need no hello, this is B");
    }
}
@end

//---------------------------------------------------------------------
//                             測試函數
//---------------------------------------------------------------------
void S4Tester(void) {
    puts("-----------------------------------------");
    puts("                  S4");
    puts("-----------------------------------------");
    id aTemp = [[S4_A alloc] init];
    [aTemp getLocationOfHierarchy];
    [aTemp getLocationOfHierarchy:NO];
    [aTemp getLocationOfHierarchy:YES];
    
    id bTemp = [[S4_B alloc] init];
    [bTemp getLocationOfHierarchy];
    [bTemp getLocationOfHierarchy:NO];
    [bTemp getLocationOfHierarchy:YES];
    
}

運行結果

-----------------------------------------
                  S4
-----------------------------------------
this is A
need no hello, this is A
hello, this is A
this is B
need no hello, this is B
hello, this is B
Program ended with exit code: 0

多態就是動態結合

優點: 不用對每一個具體對象改變現有代碼 p60

實例變量的封裝