The basic of Java-Extends,Encapsulation,Abstract,Object,Singleton,Static(Day04)

原创于 2021-08-19 11:09:08 发布 · 169 阅读

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本文详细解读了Java中静态变量的存储位置、静态块与构造器的区别，以及final关键字的使用规则。特别强调了字符串类型在不同版本中的存储变化。此外，还介绍了Integer类的两种转换方法及其区别。读者将对类的静态概念有更深入的理解。

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1. We cannot create local variables in 'static' method, since local variables are existed in stack, and they will be destroyed when the method are down, conversely, 'static' stored in method area.

2. Static block will be executed before constructor, because it implemented when a class begin to execute, so they only create one time. By contrary, constructor only created after we instantiate object, but they can execute without limitation.

3. A variable modified by 'final', it only can assign when we declare it at the beginning or in constructor.

4. Field == member variables

5. The type of String is stored in constant pool. Storing in the method area(before jdk version 1.7), and than in heap(after version 1.8)

6. Wrapper Class: Integer,parseInt() -- String convert into int(int)

Integer.valueOf() -- String convert into int(Integer)

7. We cannot use 'this' in a static method, since static method belong to class type, and 'this' is object, so