[Objective-C] class inheritance in OC

1: Why is there an inheritance relationship? Defines a common class and basic instance variables. Sub-classes can inherit the class to own these instance variables. Subclass can also define its own instance variables.   The inherited class is called superclass or parent class, And the inherited class is called subclass ). The syntax rules inherited in OC are: @ Interface subclass: parent class 2: Check the instance code. First, ClassA. h   /// ClassA. h // ClassAB // Created by hmjiangqq on 14-1-22. // Copyright (c) 2014 hmjiangqq. all rights reserved. // # import @ Interface ClassA: NSObject {int x;}-(void) initVar; @ end ClassA.m /// ClassA. m // ClassAB // Created by hmjiangqq on 14-1-22. // Copyright (c) 2014 hmjiangqq. all rights reserved. // # import "ClassA. h "@ implementation ClassA-(void) initVar {x = 100;} @ end ClassB. h /// ClassB. h // ClassAB // Created by hmjiangqq on 14-1-22. // Copyright (c) 2014 hmjiangqq. all rights reserved. // # import "ClassA. h "@ interface ClassB: ClassA-(void) printVar; @ end ClassB. m /// ClassB. m // ClassAB // Created by hmjiangqq on 14-1-22. // Copyright (c) 2014 hmjiangqq. all rights reserved. // # import "ClassB. h "@ implementation ClassB-(void) printVar {NSLog (@" x = % d \ n ", x) ;}@ end Main. m //// Main. m // ClassAB // Created by hmjiangqq on 14-1-22. // Copyright (c) 2014 hmjiangqq. all rights reserved. // # import # Import "ClassB. h" int main (int argc, const char * argv []) {@ autoreleasepool {// insert code here... NSLog (@ "Hello, World! "); ClassB * B = [[ClassB alloc] init]; [B initVar]; // method in the parent class [B printVar];} return 0 ;}