数组是线性结构是容器类型,是一块连续的内存空间, ios 中用 nsarray 和 nsmutablearray 集合类型,用来存放对象类型,其中 nsarray是不可变类型, nsmutablearray 是可变类型,能够对数组中元素进行增删改查.
本文作者本着学习的态度,决定仿照nsarray和nsmutablearray 自己实现一个数组类型,当然性能可能没有 nsarray和nsmutablearray 的好,插入100000万条数据,时间上是 nsmutablearray 的三倍左右 ,当然平时使用过程中很少100000次这样大的数据往数组里添加,因此性能方面可以忽略.
arraylist.h 主要方法声明 完全照搬 nsarray 和 nsmutablearray 的方法名称
先发下测试结果
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dispatch_async(dispatch_get_global_queue(0, 0), ^{
person *p1 = [[person alloc] init];
nsmutablearray *array = [nsmutablearray arraywithcapacity:100000];
// arraylist
*array = [arraylist arraywithcapacity:100000];
cfabsolutetime starttime =cfabsolutetimegetcurrent();
for (int i = 0; i<100000; i++) {
[array addobject:p1];
}
cfabsolutetime linktime = (cfabsolutetimegetcurrent() - starttime);
cftimeinterval duration = linktime * 1000.0f;
nslog(@"linked in %f ms",duration);
[self->_timearray addobject:@(duration)];
count++;
});
nsmutablearray 5.081740292635832 ms
arraylist 16.27591523257168 ms
以下是 arraylist 的具体实现 ,内部是一个 c语言的数组用来存放对象
//
// arraylist.m
// arraylist
//
// created by dzb on 2018/7/19.
// copyright © 2018 大兵布莱恩特. all rights reserved.
//
#import "arraylist.h"
static nsinteger const defaultcapacity = 10;
typedef void * anyobject;
@interface arraylist ()
{
anyobject *_array;
nsinteger _size;
nsinteger _capacity;
}
@end
@implementation arraylist
#pragma mark - init
- (instancetype)init
{
self = [super init];
if (self) {
[self resetarray];
}
return self;
}
+ (instancetype)array {
return [[arraylist alloc] initwithcapacity:defaultcapacity];
}
+ (instancetype)arraywithcapacity:(nsuinteger)numitems {
return [[arraylist alloc] initwithcapacity:numitems];
}
- (instancetype)initwithcapacity:(nsuinteger)numitems {
_capacity = numitems;
_array = calloc(_capacity,sizeof(anyobject));
_size = 0;
return self;
}
/**
数组重置
*/
- (void) resetarray {
_size = 0;
if (_array != null)
_array[_size] = null;
free(_array);
_capacity = defaultcapacity;
_array = calloc(_capacity, sizeof(anyobject));
}
#pragma makr - 增加操作
- (void)addobject:(id)anobject {
[self insertobject:anobject atindex:_size];
}
- (void)insertobject:(id)anobject atindex:(nsuinteger)index {
if (!anobject) {
@throw [nsexception exceptionwithname:@"add object null." reason:@"object must be not null ." userinfo:nil];
return;
}
///判越界
if ((index > _size)) {
@throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
return;
}
if (_size == _capacity-1) { ///判断原来数组是否已经满了 如果满了就需要增加数组长度
[self resize:2*_capacity];
}
///交换索引位置
if (self.count > 0 ) {
for(nsinteger i = _size - 1 ; i >= index ; i--)
_array[i + 1] = _array[i];
}
self->_array[index] = (__bridge_retained anyobject)(anobject);
_size++;
}
#pragma mark - 删除操作
- (void)removeallobjects {
nsinteger i = _size-1;
while (_size > 0) {
[self removeobjectatindex:i];
i--;
}
[self resetarray];
}
- (void)removeobjectatindex:(nsuinteger)index {
///判断越界
if ((index > _size)) {
@throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
return;
}
anyobject object =(_array[index]);
cfrelease(object);
for(nsinteger i = index + 1 ; i < _size ; i ++)
_array[i - 1] = _array[i];
_size--;
_array[_size] = null;
///对数组空间缩减
if (_size == _capacity/2) {
[self resize:_capacity/2];
}
}
- (void)removeobject:(id)anobject {
nsinteger index = [self indexofobject:anobject];
if (index == nsnotfound) return;
[self removeobjectatindex:index];
}
- (void)removelastobject {
if ([self isempty]) return;
[self removeobjectatindex:_size-1];
}
#pragma mark - 修改操作
- (void)replaceobjectatindex:(nsuinteger)index withobject:(id)anobject {
if (!anobject) {
@throw [nsexception exceptionwithname:@"add object null." reason:@"object must be not null ." userinfo:nil];
return;
}
///判断越界
if ((index > _size)) {
@throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
return;
}
_array[index] = (__bridge anyobject)(anobject);
}
#pragma mark - 查询操作
- (bool) isempty {
return (self->_size == 0);
}
- (bool) isfull {
return (self->_size == self->_capacity-1);
}
- (id)objectatindex:(nsuinteger)index {
if ((index > _size)) {
@throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
return nil;
}
if ([self isempty]) { return nil; }
anyobject obj = _array[index];
if (obj == null) return nil;
return (__bridge id)(obj);
}
- (nsuinteger)indexofobject:(id)anobject {
for (int i = 0; i<_size; i++) {
id obj = (__bridge id)(_array[i]);
if ([anobject isequal:obj]) return i;
}
return nsnotfound;
}
- (bool)containsobject:(id)anobject {
for (int i = 0; i<_size; i++) {
id obj = (__bridge id)(_array[i]);
if ([anobject isequal:obj]) return yes;
}
return no;
}
- (id)firstobject {
if ([self isempty]) return nil;
return (__bridge id _nullable)(_array[0]);
}
- (id)lastobject {
if ([self isempty]) return nil;
return (__bridge id _nullable)(_array[_size]);
}
- (nsuinteger)count {
return _size;
}
- (nsstring *)description {
nsmutablestring *string = [nsmutablestring stringwithformat:@"\narraylist %p : [ \n" ,self];
for (int i = 0; i<_size; i++) {
anyobject obj = _array[i];
[string appendformat:@"%@",(__bridge id)obj];
if (i<_size-1) {
[string appendstring:@" , \n"];
}
}
[string appendstring:@"\n]\n"];
return string;
}
/**
对数组扩容
@param capacity 新的容量
*/
- (void) resize:(nsinteger)capacity {
anyobject *oldarray = _array;
anyobject *newarray = calloc(capacity, sizeof(anyobject));
for (int i = 0 ; i<_size; i++) {
newarray[i] = oldarray[i];
}
_array = newarray;
_capacity = capacity;
free(oldarray);
}
- (void)dealloc
{
if (_array != null)
[self removeallobjects];
free(_array);
// nslog(@"arraylist dealloc");
}
@end
经过测试 数组内部会对存入的对象 进行 retain 操作 其引用计数+1 ,当对象从数组中移除的时候 能够正常的使对象内存引用计数-1,因此不必担心对象内存管理的问题. 数组默认长度是10 , 如果在开发者不确定数组长度时候 ,其内部可以动态的扩容增加数组长度,当执行 remove 操作时候 也会对数组内部长度 进行相应的缩减
实现了 nsarray 和 nsmutablearray 等常用api,如果不是对性能特别在意的场景下 ,可以使用 arraylist 来存放一些数据
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