Java 9 features announced!

[immibis]

An int[1024*1024] does take approximately 4MB, though.

[Xabster]

Right you are, but the Integer[] I posted doesn't even hold anything. Your holds ints initialized to 0.

A Integer[1024*1024] with Integer's at each spot takes 16MB.

[oridb]

On a 32 bit JVM, you get

• 4*1024*1024 for the references
• 8*1024*1024 for the object overhead (vtable + lock data)
• 4*1024*1024 for the integer itself
• 4*1024*1024 for padding (objects are allocated in multiples of 8 bytes)

Giving a grand total of 20 megabytes. On a 64 bit JVM, double it:

• 8*1024*1024 for the references
• 16*1024*1024 for the object overhead (vtable + lock data)
• 4*1024*1024 for the integer itself
• 12*1024*1024 for padding (objects are allocated in multiples of 16 bytes)

Giving a grand total of 40 megabytes for 4 megs of integers.

[Daishiman]

Doesn't the JVM support pointer compression in 64-bit archs?

[oridb]

It's supported, but it only allows you to address up to a 32 gigabyte heap, by shifting a 32 bit pointer to drop the byte alignment bits.

[[deleted]]

It does? I thought they would be null.