JDK Source Reading Notes Java Collection framework (ii) (ArrayList)

An analysis of ArrayList will start with the Add and remove methods only.

ArrayList class definition:

 Public class extends Implements List<e>

ArrayList Basic Properties:

 　 /*** Default initial capacity. (Defaults to the size of the initialization)*/    Private Static Final intDefault_capacity = 10; /*** Shared Empty array instance used for empty instances. * An empty array, which is given an empty array by default when the parameterless constructor is called*/    Private Static Finalobject[] Empty_elementdata = {}; /*** An array of truly stored data*/    Private transientobject[] Elementdata; /*** The size of the ArrayList (the number of elements it contains). * The number of data stored*/

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ArrayList The Add method:

/*** Appends the specified element to the end of this list. * Insert data, each time it is inserted from the end*/     Public BooleanAdd (e e) {ensurecapacityinternal (size+ 1);//increments modcount!!elementdata[size++] =e; return true; }Private voidEnsurecapacityinternal (intmincapacity) {        if(Elementdata = = Empty_elementdata) {//If an empty array is represented hereMincapacity =Math.max (default_capacity, mincapacity);    } ensureexplicitcapacity (mincapacity); } Private voidEnsureexplicitcapacity (intmincapacity) {Modcount++;//JDK Source Reading Notes Java Collection Framework (iii) (MODCOUNT)       if(Mincapacity-elementdata.length > 0)            /*** mincapacity=size+1 * Only used when the array actually stores the number of elements +1 is greater than the array length is, needs to be enlarged*/grow (mincapacity); }    /*** Increases the capacity to ensure so it can hold on least the * number of elements specified by the Minimu     M capacity argument. * Increase the capacity of the array to ensure that at least minimum amount of data can be stored*/    Private voidGrowintmincapacity) {        intOldcapacity =elementdata.length; //A signed right shift is equivalent to dividing by 2, so after each expansion, the array is 1.5 times times the length of the original.         intNewcapacity = oldcapacity + (oldcapacity >> 1); if(Newcapacity-mincapacity < 0) newcapacity=mincapacity; if(Newcapacity-max_array_size > 0) newcapacity=hugecapacity (mincapacity); //because of the new array generated after the expansion, here is the transfer of data between the old and new arraysElementdata =arrays.copyof (Elementdata, newcapacity); }

ArrayList the Remove method:

The Remove method is divided into remove (Object O) and remove (int index). The two methods are similar, so either one is selected for analysis.

 /*** Remove the element that specifies the subscript*/     PublicE Remove (intindex) {Rangecheck (index);//Subscript out of bounds checkModcount++;//"http://www.cnblogs.com/jw93/p/6845825.html"Detailed IntroductionE OldValue =Elementdata (index); /*** After removing an element, you need to move the element following the element forward * nummoved indicates the number of elements that need to be moved*/        intnummoved = size-index-1; if(nummoved > 0) system.arraycopy (elementdata, index+1, Elementdata, Index, nummoved);//here is the native methodElementdata[--size] =NULL;//clear to let GC do it work        returnOldValue; }    /*** Subscript cross-border check*/    Private voidRangecheck (intindex) {        if(Index >=size)Throw NewIndexoutofboundsexception (outofboundsmsg (index));//throw array subscript out of bounds    }    /*** Details when throwing exceptions*/    PrivateString Outofboundsmsg (intindex) {        return"Index:" +index+ ", Size:" +size; }

JDK Source Reading Notes Java Collection framework (ii) (ArrayList)