一个布尔值的Java中的数组不是一个独立的变量更小？ [英] Is an array of one boolean in Java smaller than a standalone variable?

问题描述

我对SO搜索都失败了我，所以如果这是一个重复的，请重定向我。

My searches on SO have failed me, so if this is a duplicate, please redirect me.

有了这样的方式，我的问题：我了解到，从经验和浏览，这样一个Java 布尔存储为一个32位的 INT 如果你声明它作为一个独立的价值，但作为一个8位字节。我的问题，在这里，如下：哪个更高效的内存？难道数组的元数据，使之更大的内存比其他？

With that out of the way, my question: I learned, from experience and browsing SO that a Java boolean is stored as a 32-bit int if you declare it as a standalone value, but as an 8-bit byte if you declare it within an array. My question, here, is as follows: Which is more memory efficient? Does the meta data of the array make it bigger in memory than the alternative?

boolean oneVariable = false, oneArray[] = {false};

推荐答案

阵列的元数据包括用于开销阵列的长度为8个字节（通用于所有的对象）和4个字节（32位）（特定于一个32位JVM阵列对象）。

The "meta data" of the array includes 8 bytes for overhead (common to all objects) and 4 bytes (32 bits) for the length of the array (specific to array objects) on a 32-bit JVM.

在8字节的倍数此外，对象分配内存，所以尽管你只需要12字节的开销+ 1字节为布尔，你会最终使用16字节的内存为您的数组对象。

Additionally, objects are allocated memory in 8-byte multiples, so even though you only need 12 bytes of overhead + 1 byte for the boolean, you'll end up using 16 bytes of memory for your array object.

在除了16个字节本身占用的对象，你将需要4个字节为对象的内存地址，共计20个字节的内存，您的布尔存放在数组中。

In addition to the 16 bytes the object itself will take up, you'll need 4 bytes for the memory address of the object, totalling 20 bytes of memory to store your boolean in an array.

因此​​，该阵列为约5倍昂贵单个布尔值。

So, the array is about 5 times as expensive for a single boolean.

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