Class Back

• 屬性有默認值且可直接初始化(C++需要用在構造函數初始化)
• 一旦函數有構造函數Constructor, 默認的Constructor將失效
• 可以通過調用super來調用父類

The order of Initialization

Override & Overload

Polymorphism

• 多態的理解: 指不同對象處理同一事件的方式並不同

eg.貓與狗同屬於動物類, 動物有叫的方法. 但是對於貓和狗來說, 叫的方式不同.

• 多態的本質: Dynamic Binding(動態綁定)
• Upcast: Base_Class p = new Derived_Class();

Inheritance

• 抽象類與接口都不能實例化
• 一個類只能繼承一個抽象類,原因菱形多重繼承存在二義性
• 一個類可以實現多個接口(間接實現多重繼承)
• 抽象類中可以有已經實現的方法, 但接口中不能實現方法
• 接口中的所有成員均為public
• 先extends, 後implements

Super Class:

class Super_Class
{
    protected void method()
    {
        //method of superclass
    }
}

class Sub_Class
{
    @Override
    //@Override起到斷言作用，檢測所重寫的方法是否拼寫正確，否則報錯。若無該句，編譯器會認為這是新方法
    public void method()
    {
        //method of subclass
    }
}

Abstract Class:

abstract class Abstract_Class
{
    public abstract void method();
}

class Derived_Class extends Abstract_Class
{
    //(override)...
    public void method(){//...} //子類重寫的函數訪問級別不能比父類低
}

Interface:

class Derived_Class implements Iinterface
{
    //(implements)...
}

Specifers: Static & Final

Static

• static成員給所有該類中的成員提供訪問性,且可以保證唯一性(構造函數私有)
• 可直接通過類名調用static成員

Final

Access Specifers: Public, Private, Protected & Omitted

Member

Class

How to get the type of an instance

Student me = new Student("PuiMan Cheui", "13121215");
System.out.println(me.getClass().getName());

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