Final static variables operations, compile or runtime?

Question

Do final static variables operations happen in run-time or compile time ? For example:

public static final int ID_1 = 1;
public static final int ID_2 = 2;

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Answer 1

It's a compile time operation (I get a method local iconst_3 below). We can directly examine the generated bytecode with javap -v. I created a class Main like,

package com.stackoverflow;

public class Main {
    public static final int ID_1 = 1;
    public static final int ID_2 = 2;

    public static int test() {
        return ID_1 + ID_2; // <-- Compile time.
    }
}

and then ran javap -v to get

Classfile /home/efrisch/workspace/StackOverflow/bin/com/stackoverflow/Main.class
  Last modified Aug 22, 2015; size 410 bytes
  MD5 checksum 6ba30603e8f16cbebc681a84061d38c3
  Compiled from "Main.java"
public class com.stackoverflow.Main
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Class              #2             // com/stackoverflow/Main
   #2 = Utf8               com/stackoverflow/Main
   #3 = Class              #4             // java/lang/Object
   #4 = Utf8               java/lang/Object
   #5 = Utf8               ID_1
   #6 = Utf8               I
   #7 = Utf8               ConstantValue
   #8 = Integer            1
   #9 = Utf8               ID_2
  #10 = Integer            2
  #11 = Utf8               
  #12 = Utf8               ()V
  #13 = Utf8               Code
  #14 = Methodref          #3.#15         // java/lang/Object."":()V
  #15 = NameAndType        #11:#12        // "":()V
  #16 = Utf8               LineNumberTable
  #17 = Utf8               LocalVariableTable
  #18 = Utf8               this
  #19 = Utf8               Lcom/stackoverflow/Main;
  #20 = Utf8               test
  #21 = Utf8               ()I
  #22 = Utf8               SourceFile
  #23 = Utf8               Main.java
{
  public static final int ID_1;
    descriptor: I
    flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL
    ConstantValue: int 1

  public static final int ID_2;
    descriptor: I
    flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL
    ConstantValue: int 2

  public com.stackoverflow.Main();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #14                 // Method java/lang/Object."":()V
         4: return
      LineNumberTable:
        line 4: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lcom/stackoverflow/Main;

  public static int test();
    descriptor: ()I
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=0, args_size=0
         0: iconst_3
         1: ireturn
      LineNumberTable:
        line 9: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
}
SourceFile: "Main.java"