Question

I would like to know how to place a local variable in memory? In method1, do the variable take a place into memory, one time?
In method2, do the variable take a place after deleting old place in memory, for each time?

public void method1() {
    Object obj = null;
    for(.....) {
        obj = come from other-->

    }
}

public void method2() {
    for(.....) {
        Object obj = come from other-->
    }
}

Answer 1

You have a local variables which may be in a register or once in memory.

You also have an object which the local variable references. This will be created on each iteration in both cases.

They are effectively the same, except I would prefer the second case if it is possible as it narrows the scope of the local variable.