From 8222fd6430aebe7caaa8320f9f40dab548c1de71 Mon Sep 17 00:00:00 2001 From: haoxiqiang Date: Fri, 13 Mar 2015 18:23:19 +0800 Subject: [PATCH] 1.add iterator --- iterator/README.md | 4 +- iterator/haoxiqiang/AndroidMileage.java | 113 ++++++++++++++++ iterator/haoxiqiang/iterator_2.jpg | Bin 0 -> 17099 bytes iterator/haoxiqiang/readme.md | 169 ++++++++++++++++++++++++ 4 files changed, 285 insertions(+), 1 deletion(-) create mode 100644 iterator/haoxiqiang/AndroidMileage.java create mode 100644 iterator/haoxiqiang/iterator_2.jpg create mode 100644 iterator/haoxiqiang/readme.md diff --git a/iterator/README.md b/iterator/README.md index 0154882..c550b77 100644 --- a/iterator/README.md +++ b/iterator/README.md @@ -1,7 +1,9 @@ # 任务表 | 作者 | 预计完成时间 | | ------------- |:-------------:| -| [用户名](git地址) | 完成时间 | +| [haoxiqiang](https://github.com/Haoxiqiang) | 2015年3月13日 | + + diff --git a/iterator/haoxiqiang/AndroidMileage.java b/iterator/haoxiqiang/AndroidMileage.java new file mode 100644 index 0000000..2bd631b --- /dev/null +++ b/iterator/haoxiqiang/AndroidMileage.java @@ -0,0 +1,113 @@ +package com.yuexue.tifenapp.wxapi; + +import android.os.Build; + +import org.apache.http.NameValuePair; + +import java.util.Iterator; + +/** + * Created by haoxiqiang on 15/3/13. + */ +public class AndroidMileage { + + final static int[] versionCodes; + final static String[] versionMileages; + final static int size; + + static { + versionCodes = new int[]{ + Build.VERSION_CODES.BASE, Build.VERSION_CODES.BASE_1_1, Build.VERSION_CODES.CUPCAKE, + Build.VERSION_CODES.DONUT, Build.VERSION_CODES.ECLAIR, Build.VERSION_CODES.ECLAIR_0_1, + Build.VERSION_CODES.ECLAIR_MR1, Build.VERSION_CODES.FROYO, Build.VERSION_CODES.GINGERBREAD, + Build.VERSION_CODES.GINGERBREAD_MR1, Build.VERSION_CODES.HONEYCOMB, Build.VERSION_CODES.HONEYCOMB_MR1, + Build.VERSION_CODES.HONEYCOMB_MR2, Build.VERSION_CODES.ICE_CREAM_SANDWICH, Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1, + Build.VERSION_CODES.JELLY_BEAN, Build.VERSION_CODES.JELLY_BEAN_MR1, Build.VERSION_CODES.JELLY_BEAN_MR2, + Build.VERSION_CODES.KITKAT, Build.VERSION_CODES.KITKAT_WATCH, Build.VERSION_CODES.LOLLIPOP + }; + versionMileages = new String[]{ + "October 2008: The original, first, version of Android. Yay!", + "February 2009: First Android update, officially called 1.1.", + " May 2009: Android 1.5.", + "September 2009: Android 1.6.", + "November 2009: Android 2.0", + "December 2009: Android 2.0.1", + "January 2010: Android 2.1", + "June 2010: Android 2.2", + "November 2010: Android 2.3", + "February 2011: Android 2.3.3.", + "February 2011: Android 3.0.", + "May 2011: Android 3.1.", + "June 2011: Android 3.2.", + "October 2011: Android 4.0.", + "December 2011: Android 4.0.3.", + "June 2012: Android 4.1.", + "November 2012: Android 4.2, Moar jelly beans!", + "July 2013: Android 4.3, the revenge of the beans.", + "October 2013: Android 4.4, KitKat, another tasty treat.", + "Android 4.4W: KitKat for watches, snacks on the run.", + "Lollipop. A flat one with beautiful shadows. But still tasty.", + }; + + size = Math.min(versionCodes.length, versionMileages.length); + } + + public static class Mileage implements NameValuePair { + + public String name; + public String value; + + @Override + public String getName() { + return name; + } + + @Override + public String getValue() { + return value; + } + + @Override + public String toString() { + return "versionCode:" + name + " desc:" + value; + } + } + + + public Iterator iterator() { + return new ArrayIterator(); + } + + private class ArrayIterator implements Iterator { + /** + * Number of elements remaining in this iteration + */ + private int remaining = size; + + /** + * Index of element that remove() would remove, or -1 if no such elt + */ + private int removalIndex = -1; + + @Override + public boolean hasNext() { + return remaining != 0; + } + + @Override + public Mileage next() { + Mileage mileage = new Mileage(); + removalIndex = size-remaining; + mileage.name = String.valueOf(versionCodes[removalIndex]); + mileage.value = versionMileages[removalIndex]; + remaining-=1; + return mileage; + } + + @Override + public void remove() { + versionCodes[removalIndex]=-1; + versionMileages[removalIndex]="It was set null"; + } + } +} diff --git a/iterator/haoxiqiang/iterator_2.jpg b/iterator/haoxiqiang/iterator_2.jpg new file mode 100644 index 0000000000000000000000000000000000000000..256f06038ea79d209c1c2a1206486439ece83503 GIT binary patch literal 17099 zcmch;2UJu0wl5rdlPX=R1R*p9rS~8u2{k|vLa`w=^dcZdq)3MlK&46VMI>|tk&YB0 z)X;lJnjnZg_Bs2UeeV6vd-uCvaD|2Eg`^EWRiF6RMsPz{I%fPjDi@bKyj zxWoh00Hnkuq$I?oq$H$dWTfPjbd;176qJlKwAbiZ7+G0a7@3*bIr+KSZ}4$2GxLb> z@ZAys34z$SMem3T-r*Mn30}4WsK^PV2tE)H&;u^p0UQ7V00GI>5`TTj2#Bs0Atb;0 z^%)(2fQX2YkeG~|oQ{H=>gvCQM8p6RdQt{5-s_Ca;x|tmTLK-HzM#*IDr)Gv=}-@6x3 z)$zj)?}^S$p31x@|@7Krmb{(N1O(k{#~NX ztTW4$XI+T6(3ff3gD!jJHGd~e){4O%{qf2;Y|djPqa#1&Y{^$b?w0StN+{*P?D<$BQR-%e^Ocl)&ozNX0?W{=_#xo+qreXnFjYGv0^F8Mq@ zjppg;;rxkvk;Fe=tUk`LRW-5QS)-~x&;-_ 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zvfzrSv~mYzN{9b^nxy?lj9>ZosuLFEFBj}qGlDf;StgR)NwI)Y6ZXXlKX%K-#Oo^F zYJ#}x-aCAX5tJV0vY1~>ITu_$Nb@%L?E>XlGfrz9X;g`G`xHDHpkOLf!4{Z*HG7_rX&a@! za)$xOXW89@@$eaUcR?z%q&h+xfWfriRih51^tJl^nDdX{Vxh8%Yb_(D9)I;9{^vWP zDB!g``M5-x63}eeP{`fyq}S`!dLpZnIl=mgd#Ucz&F|6fGjS}Dh51|t9wE6-wo(L^ zFPhGqB|Vn~I_p5{8u5sK^Z0E<$Sq7iilL5rs{%x^WjY;zg0Yb&_yc#^n8YLB+ z;lOhM=_VrnN#<|vBZPeQ*;I>rvBJrr>;9*NDhwS%S(kgrB_L9>pbz1j(`zuz4mdfz szw|CHM(`Pyrt?=O=l{lC#pUGx0IDPeCIA2c literal 0 HcmV?d00001 diff --git a/iterator/haoxiqiang/readme.md b/iterator/haoxiqiang/readme.md new file mode 100644 index 0000000..7e0b6ce --- /dev/null +++ b/iterator/haoxiqiang/readme.md @@ -0,0 +1,169 @@ +Android设计模式源码解析之迭代器(Iterator)模式 +======================================== +> 本文为 [Android 设计模式源码解析](https://github.com/simple-android-framework-exchange/android_design_patterns_analysis) 中 迭代器模式 分析 +> Android系统版本： 5.0 +> 分析者： [haoxiqiang](https://github.com/Haoxiqiang)，分析状态：完成，校对者：，校对状态：未完成 + + + +## 1. 模式介绍 +### 模式的定义 +迭代器（Iterator）模式，又叫做游标（Cursor）模式。GOF给出的定义为：提供一种方法访问一个容器（container）对象中各个元素，而又不需暴露该对象的内部细节。 + +### 使用场景 +　　面向对象设计原则中的单一职责原则，对于不同的功能,我们要尽可能的把这个功能分解出单一的职责，不同的类去承担不同的职责。Iterator模式就是分离了集合对象的遍历行为，抽象出一个迭代器类来负责，这样不暴露集合的内部结构，又可让外部代码透明的访问集合内部的数据。 +　　Java JDK 1.2 版开始支持迭代器。每一个迭代器提供next()以及hasNext()方法，同时也支持remove()(1.8的时候remove已经成为default throw new UnsupportedOperationException("remove"))。对Android来说,集合Collection实现了Iterable接口,就是说,无论是List的一大家子还是Map的一大家子,我们都可以使用Iterator来遍历里面的元素,[可以使用Iterator的集合](http://docs.oracle.com/javase/8/docs/api/java/util/package-tree.html) + +## 2. UML类图 +　　　 +　![iterator_2.png](iterator_2.jpg) + +### 角色介绍　　 +* hasNext:用来判断集合中是否存在未被遍历到的元素 +* remove:移除元素 +* next:将游标(位置)移动到下一个位置 + + +## 3. 模式的简单实现 + +下面直接写出几种集合的遍历方式 + +### HashMap的遍历 +``` +HashMap colorMap=new HashMap<>(); +colorMap.put("Color1","Red"); +colorMap.put("Color2","Blue"); +Iterator iterator = colorMap.keySet().iterator(); +while( iterator. hasNext() ){ + String key = (String) iterator.next(); + String value = colorMap.get(key); +} +``` +### JSONObject的遍历 +``` +String paramString = "{menu:{\"1\":\"sql\", \"2\":\"android\", \"3\":\"mvc\"}}"; +JSONObject menuJSONObj = new JSONObject(paramString); +JSONObject menuObj = menuJSONObj.getJSONObject("menu"); +Iterator iter = menuObj.keys(); +while(iter.hasNext()){ + String key = (String)iter.next(); + String value = menuObj.getString(key); +} +``` +下面我们自己实现一个Iterator的集合 + +``` +... +public Iterator iterator() { + return new ArrayIterator(); +} + +private class ArrayIterator implements Iterator { +/** + * Number of elements remaining in this iteration + */ +private int remaining = size; + +/** + * Index of element that remove() would remove, or -1 if no such elt + */ +private int removalIndex = -1; + +@Override +public boolean hasNext() { + return remaining != 0; +} + +@Override +public Mileage next() { + Mileage mileage = new Mileage(); + removalIndex = size-remaining; + mileage.name = String.valueOf(versionCodes[removalIndex]); + mileage.value = versionMileages[removalIndex]; + remaining-=1; + return mileage; +} + +@Override +public void remove() { + versionCodes[removalIndex]=-1; + versionMileages[removalIndex]="It was set null"; +} +} +... +``` +使用的过程如下,我们特意使用了remove方法,注意这个只是一个示例,和大多数的集合相比,该实现并不严谨 + +``` +AndroidMileage androidMileage = new AndroidMileage(); +Iterator iterator =androidMileage.iterator(); +while (iterator.hasNext()){ + AndroidMileage.Mileage mileage = iterator.next(); + if(mileage.name.equalsIgnoreCase("16")){ + //remove掉的是当前的这个,暂时只是置空,并未真的移掉 + iterator.remove(); + } + Log.e("mileage",mileage.toString()); +} +``` +### 原理分析 +一个集合想要实现Iterator很是很简单的,需要注意的是每次需要重新生成一个Iterator来进行遍历.且遍历过程是单方向的,HashMap是通过一个类似HashIterator来实现的,我们为了解释简单,这里只是研究ArrayList(此处以Android L源码为例,其他版本略有不同) + +``` +@Override public Iterator iterator() { + return new ArrayListIterator(); +} + +private class ArrayListIterator implements Iterator { + /** Number of elements remaining in this iteration */ + private int remaining = size; + + /** Index of element that remove() would remove, or -1 if no such elt */ + private int removalIndex = -1; + + /** The expected modCount value */ + private int expectedModCount = modCount; + + public boolean hasNext() { + return remaining != 0; + } + + @SuppressWarnings("unchecked") public E next() { + ArrayList ourList = ArrayList.this; + int rem = remaining; + if (ourList.modCount != expectedModCount) { + throw new ConcurrentModificationException(); + } + if (rem == 0) { + throw new NoSuchElementException(); + } + remaining = rem - 1; + return (E) ourList.array[removalIndex = ourList.size - rem]; + } + + public void remove() { + Object[] a = array; + int removalIdx = removalIndex; + if (modCount != expectedModCount) { + throw new ConcurrentModificationException(); + } + if (removalIdx < 0) { + throw new IllegalStateException(); + } + System.arraycopy(a, removalIdx + 1, a, removalIdx, remaining); + a[--size] = null; // Prevent memory leak + removalIndex = -1; + expectedModCount = ++modCount; + } +} +``` + +* java中的写法一般都是通过iterator()来生成Iterator,保证iterator()每次生成新的实例 +* remaining初始化使用整个list的size大小,removalIndex表示remove掉的位置,modCount在集合大小发生变化的时候后都会进行一次modCount++操作,避免数据不一致,前面我写的例子这方面没有写,请务必注意这点 +* hasNext方法中,因为remaining是一个size->0的变化过程,这样只需要判断非0就可以得知当前遍历的是否还有未完成的元素 +* next,第一次调用的时候返回array[0]的元素,这个过程中removalIndex会被设置成当前array的index +* remove的实现是直接操作的内存中的数据,是能够直接删掉元素的,不展开了 + +### 题外话 +如果你想写一个集合的数据结构的话,通过实现Iterator来操作集合,这样能够降低学习成本,因为你让外部代码透明的访问集合内部的数据.当然在前面的例子中,你也见到了ConcurrentModificationException这个Exception,如果你在遍历的过程中,集合发生改变,变多变少,内容变化都是算,就会抛出来这个异常. +