oc之集合对象

#import <Foundation/Foundation.h>

//使用Printing类别，将打印方法添加到NSSet
@interface NSSet (Printing)
- (void) print;
@end

@implementation NSSet (Printing)
- (void) print{
    printf("{ ");
    
    for(NSNumber *element in self)
        printf(" %li", (long) [element integerValue]);
    printf("} \n");//提醒我们如何通过创建分类将方法添加到类中
}
@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSMutableSet *set1 = [NSMutableSet setWithObjects: @1, @2, @5, @10, nil];
        NSSet *set2 = [NSSet setWithObjects:@-5, @100, @3, @5, nil];
        NSSet *set3 = [NSSet setWithObjects:@12, @200, @3, nil];//以一个nil结尾的对象数组创建新集合
        NSLog(@"set1 = ");
        [set1 print];
        NSLog(@"set2: ");
        [set2 print];
        
        //相等性测试
        if([set1 isEqualToSet: set2] == YES)//检测两个集合是否相等
            NSLog(@"set1 equals set2");
        else
            NSLog(@"set1 is not equal to set2");
        
        //成员测试
        if([set1 containsObject: @10] == YES)//查询10是否在set1中
            NSLog(@"set1 contains 10");
        else
            NSLog(@"set1 does not contain 10");
        
        if([set2 containsObject: @10] == YES)
            NSLog(@"set2 contains 10");
        else
            NSLog(@"set2 does not contain 10");
        
        //在可变集合set1中添加移除对象
        
        [set1 addObject: @4];
        [set1 removeObject: @10];
        NSLog(@"set1 after adding 4 and removing 10:");
        [set1 print];
        
        //获得两个集合的交集
        
        [set1 intersectSet: set2];
        NSLog(@"set1 intersect set2: ");
        [set1 print];
        //两个集合的并集
        [set1 unionSet: set3];
        NSLog(@"set1 union set3: ");
        [set1 print];
        //在这两种情况下，运算结果取代了消息的接收者（set1)改变
    }
    return 0;
}

 
  Foundation框架同样提供了一个名为NSCountedSet的类。这种集合同一对象可以出现多次，然而并非在集合中存放多次这个对象，而是维护一个次数计数。当第一次将对象添加到集合时，对象的count值被置为1，然后每次将这个对象添加到集合中,count值就会增1，每次从集合删除对象，count值就会减1.当对象的count值为0时，实际上对象本身就被删除了。使用方法countForObject:可以在集合中检索某个对象count值。重要应用是单词计数器。 
 

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