Does java uses memory in case of integer/Double/Float number usage

Question

I am facing a confusion hope anyone might answer. Please see the code below

for(int i = 0; i < 40; i++){
    if(i < 20){  //Does this 20 here is initialized again and again
       System.out.println("less than 20");
    }else{
       System.out.println("greater than 20");
    }
}

So my question is: Does the 20 in i < 20 gets initialized to an integer again and again causing allocation of memory again and again or does java uses similar kind of concept like a STRING POOL it uses for string.

According to knowledge it takes memory, but I still want to be sure. The reason for that is:

I am working on a code which is too much performance intensive, hence I cannot add conditional code in it. Something like below

 for(int p = 0; p < 10; p++){
            if(p < 20){
                System.out.println("ABC");
            }
            if(p < 20 && "SomeValue".equals("SomeValue")){
                System.out.println("SomeValue");
            }
            if(p < 20 && "ABC".equals("ABC")){
                System.out.println("ABCDEF");
            }
        }

so if the answer is yes that 20 is taking the memory then I can make the code something like below

 int value = ("Coldrink".equals("coca cola"))?10:20;
        for(int p = 0; p < 10; p++){
            if(p < value){
                System.out.println("ABC");
            }
            if(p < value && "SomeValue".equals("SomeValue")){
                System.out.println("SomeValue");
            }
            if(p < value && "ABC".equals("ABC")){
                System.out.println("ABCDEF");
            }
        }

as you can see the variable value is initialized once and I have put my own condition which might have some performance issue, but then I have reduced the memory consumption, which could make things even.

EDIT: Thanks @ T.J Crowder got my confusions cleared up. People who have the same issues please read the accepted answer as well as Click on this resource too

You're overthinking this. 20 is just a constant number, just because you use that number it doesn't mean that a location in memory needs to be allocated, initialized etc. No need to worry about memory usage for this case. Don't put the value in an `int` beforehand - that is actually worse than your first solution. — Jesper, Apr 04 '17 at 13:18
When you're writing real performance intensive code, you use a profiler. You don't start blindly guessing whether some irrelevant `20` is slowing your program down. — Kayaman, Apr 04 '17 at 13:18
As i wrote that I had a confusion. And @Jesper could you explain why the second solution is not good. If that's the case then I might have to think something else. — Anant666, Apr 04 '17 at 13:25
Because it's more code and doesn't change anything, specifically it does not make the program more efficient or cause less memory use. — Jesper, Apr 04 '17 at 13:35

score 8 · Accepted Answer · answered Apr 04 '17 at 13:18

Does the 20 in i < 20 gets initialized to an integer again and again causing allocation of memory again and again or does java uses similar kind of concept like a STRING POOL it uses for string.

Neither. The 20 is a primitive int value — not an Integer instance — which is hardcoded in the bytecode and loaded into a register for the comparison operation. No need for anything like the string intern pool, and no new allocation for each iteration.

We can see this by putting that loop in a main in an example class:

public class Example {
    public static void main(String[] args) {
        for(int i = 0; i < 40; i++){
            if(i < 20){  //Does this 20 here is initialized again and again
               System.out.println("less than 20");
            }else{
               System.out.println("greater than 20");
            }
        }
    }
}

...then compiling it, and looking at the bytecode via javap -c Example:

Compiled from "Example.java"
public class Example {
  public Example();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: iconst_0
       1: istore_1
       2: iload_1
       3: bipush        40
       5: if_icmpge     39
       8: iload_1
       9: bipush        20
      11: if_icmpge     25
      14: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
      17: ldc           #3                  // String less than 20
      19: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      22: goto          33
      25: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
      28: ldc           #5                  // String greater than 20
      30: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      33: iinc          1, 1
      36: goto          2
      39: return
}

Note the boldfaced operations at offsets 9 and 11.

Great explanation @T.J. Crowder. It cleared my confusion. I think I have to change my approach. +1 for this clear and detailed answer. — Anant666, Apr 04 '17 at 13:23

Does java uses memory in case of integer/Double/Float number usage

1 Answers1