Thủ thuật với các loại dung lượng lưu trữ là chuyển các đối tượng vào một cái gì đó có thể tồn tại trên các phương tiện khác, và có thể được sống lại vào một bộ nhớ RAM thường xuyên dựa trên đối tượng khi cần thiết. Java cung cấp hỗ trợ cho sự kiên trì trọng lượng nhẹ, | . This is one place in which the compiler appropriately does complain about forward referencing since this has to do with the order of initialization and not the way the program is compiled. Feedback This approach to initialization is simple and straightforward. It has the limitation that every object of type Initialvalues will get these same initialization values. Sometimes this is exactly what you need but at other times you need more flexibility. Feedback Constructor initialization The constructor can be used to perform initialization and this gives you greater flexibility in your programming since you can call methods and perform actions at run time to determine the initial values. There s one thing to keep in mind however you aren t precluding the automatic initialization which happens before the constructor is entered. So for example if you say class Counter int i Counter i 7 . . . then i will first be initialized to 0 then to 7. This is true with all the primitive types and with object references including those that are given explicit initialization at the point of definition. For this reason the compiler doesn t try to force you to initialize elements in the constructor at any particular place or before they are used initialization is already guaranteed6. Feedback Order of initialization Within a class the order of initialization is determined by the order that the variables are defined within the class. The variable definitions may be 6 In contrast C has the constructor initializer list that causes initialization to occur before entering the constructor body and is enforced for objects. See Thinking in C 2nd edition available on this book s CD ROM and at . 208 Thinking in Java scattered throughout and in between method definitions but the variables are initialized before any methods can be called even the constructor. For example Feedback c04 Demonstrates initialization order. import .
