谁能说出Java 中布尔值的位大小？
Answers:
它取决于虚拟机。
它取决于虚拟机，但是很容易将代码从类似的问题改编成关于Java中字节的问题：
class LotsOfBooleans
{
boolean a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, aa, ab, ac, ad, ae, af;
boolean b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf;
boolean c0, c1, c2, c3, c4, c5, c6, c7, c8, c9, ca, cb, cc, cd, ce, cf;
boolean d0, d1, d2, d3, d4, d5, d6, d7, d8, d9, da, db, dc, dd, de, df;
boolean e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, ea, eb, ec, ed, ee, ef;
}
class LotsOfInts
{
int a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, aa, ab, ac, ad, ae, af;
int b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf;
int c0, c1, c2, c3, c4, c5, c6, c7, c8, c9, ca, cb, cc, cd, ce, cf;
int d0, d1, d2, d3, d4, d5, d6, d7, d8, d9, da, db, dc, dd, de, df;
int e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, ea, eb, ec, ed, ee, ef;
}
public class Test
{
private static final int SIZE = 1000000;
public static void main(String[] args) throws Exception
{
LotsOfBooleans[] first = new LotsOfBooleans[SIZE];
LotsOfInts[] second = new LotsOfInts[SIZE];
System.gc();
long startMem = getMemory();
for (int i=0; i < SIZE; i++)
{
first[i] = new LotsOfBooleans();
}
System.gc();
long endMem = getMemory();
System.out.println ("Size for LotsOfBooleans: " + (endMem-startMem));
System.out.println ("Average size: " + ((endMem-startMem) / ((double)SIZE)));
System.gc();
startMem = getMemory();
for (int i=0; i < SIZE; i++)
{
second[i] = new LotsOfInts();
}
System.gc();
endMem = getMemory();
System.out.println ("Size for LotsOfInts: " + (endMem-startMem));
System.out.println ("Average size: " + ((endMem-startMem) / ((double)SIZE)));
// Make sure nothing gets collected
long total = 0;
for (int i=0; i < SIZE; i++)
{
total += (first[i].a0 ? 1 : 0) + second[i].a0;
}
System.out.println(total);
}
private static long getMemory()
{
Runtime runtime = Runtime.getRuntime();
return runtime.totalMemory() - runtime.freeMemory();
}
}重申一下，这取决于VM，但是在运行Sun的JDK build 1.6.0_11的Windows笔记本电脑上，我得到了以下结果：
Size for LotsOfBooleans: 87978576
Average size: 87.978576
Size for LotsOfInts: 328000000
Average size: 328.0这表明，Sun的JVM基本上可以将布尔值打包为一个字节。
在Java中，由布尔值表示的实际信息是一位：1表示true，0表示false。但是，Java规范没有精确定义内存中布尔变量的实际大小。请参见Java中的原始数据类型。
布尔数据类型只有两个可能的值：true和false。将此数据类型用于跟踪真/假条件的简单标志。这种数据类型代表一小部分信息，但是其“大小”并不是精确定义的。