javascript - 两个代码片段之间的内存差异

问题描述

Java 代码示例 1：

ArrayList<ArrayList<Integer>> outerList = new ArrayList<ArrayList<Integer>>();
for(i=0; i<5000; i++){  
    outerList.add(new ArrayList<Integer>());
    for(j=0; j<5000; j++){
        outerList.get(i).add(1);
    }
}

Java 代码示例 2：

ArrayList<ArrayList<Integer>> outerList_n = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> innerList_n = new ArrayList<Integer>();

for(j=0; j<5000; j++){
    innerList_n.add(1);
}   
for(i=0; i<5000; i++){  
    outerList_n.add(innerList_n);
}

说明：

代码示例 1 每次都创建一个新的 arrayList 以添加到外部列表，尽管内部列表的每个条目始终为 1。

代码示例 2 创建一个所有条目为 1 的数组，然后在 for 循环中将其添加到 outerList。

问题：

1）他们都有不同的内存占用还是相同的？我使用 jdk.nashorn.internal.ir.debug.ObjectSizeCalculator 来计算它，结果如下：

外列表大小：514907072

outerList_n 的大小：130048

2）我不明白为什么上面的内存差异。两种情况下的数据结构不一样吗？

3）这在javascript中是否相同？当我为上述两种情况尝试各自的 javascript 代码时，我在两种情况下都得到了相同的内存占用。

Javascript代码：

function sizeof(object){

  // initialise the list of objects and size
  var objects = [object];
  var size    = 0;

  // loop over the objects
  for (var index = 0; index < objects.length; index ++){

    // determine the type of the object
    switch (typeof objects[index]){

      // the object is a boolean
      case 'boolean': size += 4; break;

      // the object is a number
      case 'number': size += 8; break;

      // the object is a string
      case 'string': size += 2 * objects[index].length; break;

      // the object is a generic object
      case 'object':

        // if the object is not an array, add the sizes of the keys
        if (Object.prototype.toString.call(objects[index]) != '[object Array]'){
          for (var key in objects[index]) size += 2 * key.length;
        }

        // loop over the keys
        for (var key in objects[index]){    
          // determine whether the value has already been processed
          var processed = false;
          for (var search = 0; search < objects.length; search ++){
            if (objects[search] === objects[index][key]){
              processed = true;
              break;
            }
          }    
          // queue the value to be processed if appropriate
          if (!processed) objects.push(objects[index][key]);    
        }    
    }    
  }    
  // return the calculated size
  return size;    
}

// TWO SEPARATE FOR LOOPS
var start = new Date().getTime();
var i,j ;
var inner_arr1 = [];
var outer_arr1 = [];
for (i = 0; i < 100; i++) {
    inner_arr1.push("abcdefghijklmnopqrstuvwxyz");
}
for (j = 0; j < 100; j++) {
    outer_arr1.push(inner_arr1);
}
var end = new Date().getTime();
print("size of outer_arr1: "+sizeof(outer_arr1));
print("time of outer_arr1 (in ms): "+(end-start))


// NESTED FOR LOOPS
var start = new Date().getTime();
var outer_arr2 = [];
for (j = 0; j < 100; j++) {
    var inner_arr2 = [];    
    for (i = 0; i < 100; i++) {
        inner_arr2.push("abcdefghijklmnopqrstuvwxyz");   
    }
    outer_arr2.push(inner_arr1);    
}
var end = new Date().getTime();
print("size of outer_arr2: "+sizeof(outer_arr2));
print("time of outer_arr2 (in ms): "+(end-start))


/*
COMMAND:
jjs findingSize.js

OUTPUT:
size of outer_arr1: 52
time of outer_arr1 (in ms): 45
size of outer_arr2: 52
time of outer_arr2 (in ms): 58
*/

标签： javascriptjavamemory

javascript - 两个代码片段之间的内存差异

问题描述

解决方案

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