Memory

Stack

• First in, last out
• Every thread has its own stack
• JVM know when to destroy stack(like after one function ends)

Heap

• all objects are stored on the heap
• object in heap that can shared across multiple threads
• variable are a reference to the objects
• local variables are stored on the stack

Pass by value

• For Primitives, pass by value
• For objects, the Reference to the object is passed by value(we are passing the copy of pointer, so it still points to that object)

final keyword

• final, variable can only be assigned once
• is similar to const in C ``` final Customer c= new Customer("John"); c = new Customer("Susan"); //compile error

```

Escaping reference

• if we add records.clear() at end of this code, then it will clear the records
• it will work like this CustomerRecords is defined public instead of private, since we can direcly operate on them
• one solution is that we make this CustomerRecords directly iterable

Better way

• Still, it's not perfect way since iterator also has a remove method
• a better way is to return a new hashmap using constructor like below
• then we are not allowed to edit original object without setter
• so even we do records.getCustomers.clear(), it wont impact on original object

Improvement

• the safe way is to return immutable collections
• make it unmodifiable

Addition

• not even return original objects
• give it a new constructor and return a new object so that no edition will be on original objects