如果学过Java和C#的人，这里容易搞混，

Objective-C中的@interface关键字是申明类

@interface Circle : NSObject{    @private    ShapeColor fillColor;    ShapeRect bounds;}- (void) setFillColor: (ShapeColor) fillColor;- (void) setBounds: (ShapeRect) bounds;- (void) draw;@end // Circle

如上，这样的申明类的方式确实让我们Java和C#程序员有点不太习惯，连缩进方式也是

还是来看一下完整代码吧

#import 
     
      // --------------------------------------------------// constants for the different kinds of shapes and their colorstypedef enum {    kRedColor,    kGreenColor,    kBlueColor} ShapeColor;// --------------------------------------------------// Shape bounding rectangletypedef struct {    int x, y, width, height;} ShapeRect;// --------------------------------------------------// convert from the ShapeColor enum value to a human-readable nameNSString *colorName (ShapeColor color){    switch (color) {        case kRedColor:            return @"red";            break;        case kGreenColor:            return @"green";            break;        case kBlueColor:            return @"blue";            break;    }        return @"no clue";    } // colorName// --------------------------------------------------// All about Circles@interface Circle : NSObject{    ShapeColor  fillColor;    ShapeRect   bounds;}- (void) setFillColor: (ShapeColor) fillColor;- (void) setBounds: (ShapeRect) bounds;- (void) draw;@end // Circle@implementation Circle- (void) setFillColor: (ShapeColor) c{    fillColor = c;} // setFillColor- (void) setBounds: (ShapeRect) b{    bounds = b;} // setBounds- (void) draw{    NSLog (@"drawing a circle at (%d %d %d %d) in %@",           bounds.x, bounds.y,            bounds.width, bounds.height,           colorName(fillColor));} // draw@end // Circle// --------------------------------------------------// All about Rectangles@interface Rectangle : NSObject{    ShapeColor    fillColor;    ShapeRect    bounds;}- (void) setFillColor: (ShapeColor) fillColor;- (void) setBounds: (ShapeRect) bounds;- (void) draw;@end // Rectangle@implementation Rectangle- (void) setFillColor: (ShapeColor) c{    fillColor = c;} // setFillColor- (void) setBounds: (ShapeRect) b{    bounds = b;} // setBounds- (void) draw{    NSLog (@"drawing a rectangle at (%d %d %d %d) in %@",           bounds.x, bounds.y,            bounds.width, bounds.height,           colorName(fillColor));} // draw@end // Rectangle// --------------------------------------------------// All about OblateSphereoids@interface OblateSphereoid : NSObject{    ShapeColor    fillColor;    ShapeRect    bounds;}- (void) setFillColor: (ShapeColor) fillColor;- (void) setBounds: (ShapeRect) bounds;- (void) draw;@end // OblateSphereoid@implementation OblateSphereoid- (void) setFillColor: (ShapeColor) c{    fillColor = c;} // setFillColor- (void) setBounds: (ShapeRect) b{    bounds = b;} // setBounds- (void) draw{    NSLog (@"drawing an egg at (%d %d %d %d) in %@",           bounds.x, bounds.y,            bounds.width, bounds.height,           colorName(fillColor));} // draw@end // OblateSphereoid// --------------------------------------------------// Draw the shapesvoid drawShapes (id shapes[], int count){    for (int i = 0; i < count; i++) {        id shape = shapes[i];        [shape draw];    }    } // drawShapes// --------------------------------------------------// The main function.  Make the shapes and draw themint main (int argc, const char * argv[]) {    id shapes[3];        ShapeRect rect0 = { 0, 0, 10, 30 };    shapes[0] = [Circle new];    [shapes[0] setBounds: rect0];    [shapes[0] setFillColor: kRedColor];        ShapeRect rect1 = { 30, 40, 50, 60 };    shapes[1] = [Rectangle new];    [shapes[1] setBounds: rect1];    [shapes[1] setFillColor: kGreenColor];        ShapeRect rect2 = { 15, 19, 37, 29 };    shapes[2] = [OblateSphereoid new];    [shapes[2] setBounds: rect2];    [shapes[2] setFillColor: kBlueColor];        drawShapes (shapes, 3);        return (0);    } // main
     

运行结果：

drawing a circle at (0 0 10 30) in red

drawing a rectangle at (30 40 50 60) in green

drawing an egg at (15 19 37 29) in blue

drawing a triangle at (47 32 80 50) in red