Question

可能重复：
Java - boolean primitive type - size

我设计了这个程序来计算Java中boolean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，它表示大小为1.0000016字节。现在，Oracle Java文档说明boolean的大小“未定义”。 [见link]。为什么会这样？此外，boolean变量代表1位信息（true和false），那么剩余的7位会发生什么？

Answer 1

访问1位是一项昂贵的操作;如果从内存中检索数据，则最有可能按字或字节进行。在Java中，布尔值的内部表示是一个实现细节，除非您正在执行VM实现，否则不应该关注它。

用于计算布尔变量大小的程序

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