可能重复：
Java - 布尔原始类型 - 大小
我设计了这个程序来计算booleanJava 中 a 的大小。
public class BooleanSizeTest{
/**
* This method attempts to calculate the size of a boolean.
*/
public static void main(String[] args){
System.gc();//Request garbage collection so that any arbitrary objects are removed.
long a1, a2, a3;//The variables to hold the free memory at different times.
Runtime r = Runtime.getRuntime();//Get the runtime.
System.gc();//Request garbage collection so that any arbitrary objects are removed.
a1 = r.freeMemory();//The initial amount of free memory in bytes.
boolean[] lotsOfBools = new boolean[10_000_000];//Declare a boolean array.
a2 = r.freeMemory();
System.gc();//Request garbage collection.
a3 = r.freeMemory();// Amount of free memory after creating 10,000,000 booleans.
System.out.println("a1 = "+a1+", a2 = "+a2+", a3 = "+a3);
double bSize = (double)(a1-a2)/10_000_000;/*Calculate the size of a boolean
using the difference of a1 and a2*/
System.out.println("boolean = "+bSize);
}
}
当我运行程序时，它说大小是 1.0000016 字节。现在，Oracle Java 文档说 a 的大小boolean是“未定义的”。[见链接]。为什么会这样？另外，一个boolean变量代表 1 位信息（true和false），那么剩下的 7 位会发生什么？