用于计算布尔变量大小的程序

Question

可能重复:
Java - 布尔基元类型 - 大小

我设计了这个程序来计算booleanJava中的大小.

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？此外,boolean变量代表1位信息(true和false),那么剩下的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，您最有可能按字或按字节进行操作。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，否则您不应该关心它。