看到Java的基本类型，突然想到boolean 占几个字节？第一反应：1byte。
不确定，查之。在这个帖子上讨论过：
但众说纷纭，没有一个令人信服的，唯一的线索是： boolean的大小JVM规范并没有指定。 最后在stackoverflow上找到答案（ ）
It depends on Java virtual machine
可以用下面的代码粗略得出:
- 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 = 100000;
- 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();
- }
- }
我的机器运行结果：
Size for LotsOfBooleans: 8784984 Average size: 87.84984 Size for LotsOfInts: 32800000 Average size: 328.0
在我使用的JVM上boolean是1byte