What is the size of a boolean variable in Java?
JavaBooleanJava Problem Overview
Can any one tell the bit size of boolean in Java?
Java Solutions
Solution 1 - Java
It depends on the virtual machine, but it's easy to adapt the code from a [similar question asking about bytes in Java][1]:
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();
}
}
To reiterate, this is VM-dependent, but on my Windows laptop running Sun's JDK build 1.6.0_11 I got the following results:
Size for LotsOfBooleans: 87978576
Average size: 87.978576
Size for LotsOfInts: 328000000
Average size: 328.0
That suggests that booleans can basically be packed into a byte each by Sun's JVM. [1]: https://stackoverflow.com/questions/229886
Solution 2 - Java
It's virtual machine dependent.
Solution 3 - Java
The actual information represented by a boolean value in Java is one bit: 1 for true, 0 for false. However, the actual size of a boolean variable in memory is not precisely defined by the Java specification. See [Primitive Data Types in Java][1].
> The boolean data type has only two > possible values: true and false. Use > this data type for simple flags that > track true/false conditions. This data > type represents one bit of > information, but its "size" isn't > something that's precisely defined.
[1]: http://java.sun.com/docs/books/tutorial/java/nutsandbolts/datatypes.html "Primitive Data Types in Java"
Solution 4 - Java
On a side note...
If you are thinking about using an array of Boolean objects, don't. Use a BitSet instead - it has some performance optimisations (and some nice extra methods, allowing you to get the next set/unset bit).
Solution 5 - Java
I read that Java reserves one byte for a boolean
datatype, but it uses only one bit.
However, the documentation says that "its "size" isn't something that's precisely defined".
See here.
Solution 6 - Java
The boolean
values are compiled to int
data type in JVM. See here.
Solution 7 - Java
Size of the boolean in java is virtual machine dependent. but Any Java object is aligned to an 8 bytes granularity. A Boolean has 8 bytes of header, plus 1 byte of payload, for a total of 9 bytes of information. The JVM then rounds it up to the next multiple of 8. so the one instance of java.lang.Boolean takes up 16 bytes of memory.
Solution 8 - Java
It's undefined; doing things like Jon Skeet suggested will get you an approximation on a given platform, but the way to know precisely for a specific platform is to use a profiler.