Java Learning Note –class(1)

JavaLearning Note –class(1)

Reference: Java Tutorial (Oracle)

 

1.modifiers

 

1). comprehension

                      

Package one: Apple 公司

Package two: Foxconn公司

Alpha:              Apple 的对外关系部

Beta:               Apple的研发部

AlphaSub: Foxconn 的生产部

 

那么,标识符可以这么理解(以 Alpha 部门为例)

public

Apple产品 (iPhone, mac,…) 人人可见

protected

Apple未公布消息(iPhone 7的配置), Apple员工都知道

 Foxconn 的 AlphaSub 接到订单后(继承)也知道

default

Apple的iPhone 8研发计划, Apple员工都知道

private

 Alpha研发部的内部工作, Alpha部门的人直接操作

(getter, setter: 来自其他部门的请求)

 

2) Tips on Choosing an Access Level.

1.Use private unless you have a good reason not to.

2.Avoid public except for constants.

Conclusion:prevent unexpected invoke.

 

2. class methods

class methods

(static method)

cannot access instance variables or instance methods,

unless use an object reference.????????????

cannot use this. keyword, because there is no instance.

 

3.Initializing

{

// whatever code is needed for initialization goes here

//for instance variable, the block will be copied to every constructor.

// with static keyword, it’s used for initialize class variable

}

class Whatever {

    public static varType myVar = initializeClassVariable();      

    private static varType initializeClassVariable() {

// initialization code goes here

// can be reused later if you need to reinitialize the class variable.???????????

    }

}