JavaScript indexed array associative array and static array dynamic array

Array classification:

1, from the index of the array into the index array, associative array

var ary1 = [1,3,5,8];

//
 
 
 
 
 

//An index is really just an ordinal number, an integer number 

alert(ary1[0]);

alert(ary1[1]);

alert(ary1[2]);

alert(ary1[3]);

 



var ary2 = {};

//When accessed, it is accessed as a non-ordinal number (number), in this case a string 

ary2["one"] = 1;

ary2["two"] = 2;

ary2["thr"]  = 3;

ary2["fou"] = 4;

2. The storage of data is divided into static array and dynamic array

//Static array 
 in Java
//After the definition of the length of the array fixed can not be changed, according to the index of the array element 

Int[] ary1 = {1,3,6,9};

 

//Dynamic array in Java 

//The ArrayList implementation in Java is based on an Array, and dynamic arrays are generalized, no matter how they are implemented. < br / >
List<Integer> ary2 = new ArrayList<Integer>();

ary2.add(1);//Elements can be added dynamically, and the length of the array varies with 

ary2.add(3);

ary2.add(6);

var ary = [];//Defines an array with an unspecified length 

ary[0] = 1;//
 can be added dynamically
ary.push(3);

ary.push(5);

 

alert(ary.join(","));//Output 1,3,5 < br / >

Js array belongs to both indexed array and dynamic array, because it is essentially a js object, which embodies the dynamic language of js. However, the indexed array of js is not "continuously allocated" memory, so indexing is not very efficient. Arrays in Java allocate memory sequentially.