Do unused local variables in a method acquire memory in JVM?

Question

I came across this post in SO Do uninitialized primitive instance variables use memory?

It states \"In Java, does it cost memory to declare a class level instance va

Answer 1

Expanding slightly on the testcase from @JonKiparsky:

public class StackSlotTest {
    public int bar(){
        int a;
        a = 5;
        System.out.println("foo");
        return a;
    }

    public int foo(){
        int x;
        int a;
        a = 5;
        System.out.println("foo");
        return a;
      }
}

I added the variable a to both methods, and added a set and use of it in both.

  public int bar();
    Code:
       0: iconst_5
       1: istore_1
       2: getstatic     #2                  // Field java/lang/System.out:Ljava/
io/PrintStream;
       5: ldc           #3                  // String foo
       7: invokevirtual #4                  // Method java/io/PrintStream.printl
n:(Ljava/lang/String;)V
      10: iload_1
      11: ireturn

Above you see that the iload_1 bytecode loads the value of a to be returned. The second stack slot is referenced. (The first is the this pointer.)

  public int foo();
    Code:
       0: iconst_5
       1: istore_2
       2: getstatic     #2                  // Field java/lang/System.out:Ljava/
io/PrintStream;
       5: ldc           #3                  // String foo
       7: invokevirtual #4                  // Method java/io/PrintStream.printl
n:(Ljava/lang/String;)V
      10: iload_2
      11: ireturn

In this case the value of a is loaded with iload_2, to access the third slot, because the second slot is occupied (sort of) by the (totally unused) variable x.