share Java variable assignment and some basic concept，very important but lose them easily

1. The actual parameter (or argument expression) is fully evaluated and the resulting value is copied into a location being used to hold the formal parameter's value during method/function execution. That location is typically a chunk of memory on the runtime stack for the application (which is how Java handles it), but other languages could choose parameter storage differently. Pass-by-value

2. The formal parameter merely acts as an alias for the actual parameter. Anytime the method/function uses the formal parameter (for reading or writing), it is actually using the actual parameter . Pass-by-reference

3. Dog dog = new Dog( "Tom" ); Dog Heap

4. DogHouse house = new DogHouse(); house.assignNullToName( dog ); public void assignNullToName(Dog locDog ) Dog Dog pass-by- value or pass-by-copy Heap

5. locDog = null ; Dog Dog Heap

7. 物件參考變數 (reference variable) 保存的是 存取物件的方法

8. 物件參考變數不是物件的 container ，而是 類似 物件的指標 (pointer) 或位址 (address) ，在 Java 中我們不會也不該知道 reference variable 中真實內容是什麼，它只是用來代表單一的物件。只有 JVM 才知道如何用 reference variable 取得物件