Ikk：新頁面: 檔案:SCJP182-2.jpg the class definitions: class Animal{} class Dog extends Animal{} and the code: public void go(){ ArrayList aList = new ArrayList();...

2013-03-30T00:42:15Z

新頁面: 檔案:SCJP182-2.jpg the class definitions: class Animal{} class Dog extends Animal{} and the code: public void go(){ ArrayList<Dog> aList = new ArrayList<Dog>();...

新頁面

[[檔案:SCJP182-2.jpg]]

the class definitions:
class Animal{}
class Dog extends Animal{}
and the code:
public void go(){
ArrayList<Dog> aList = new ArrayList<Dog>();
takeList(aList);
}
//insert definition of the takeList() method here

Place the correct Compilation Result on each takeList() method definition to indicate whether
or not the go() method would compile given that definition.

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<span style="font-size:medium;">解答</span>

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<span style="font-size: medium;">Ans: <BR>[[檔案:SCJP182-1.png]] </span>

<span style="font-size:medium;"> 解說:
ArrayList<Dog> aList = new ArrayList<Dog>();
上面這條敘述是宣告一個並新增一個aList陣列型式之串列物件，其中限定此串列儲存的物件必須為Dog類別，
因此takeList這個方法要傳入aList這個串列物件，必須宣告接受內為Dog型態的串列物件：
ArrayList list 非泛型用法，不限定串列要放何種類別型態物件，所以可以接收aList

ArrayList<Animal> list 限定串列必須儲存Animal型態物件，如果要接受Animal子類別型態的話，
要使用：ArrayList < ? extends Animal> 表示可代入任何是Animal 或 Animal的子類別型態

ArrayList <Object> 也是同上解釋

ArrayList <?> 表串列中可放任一型態物件

泛型請參考黃彬華講義12章

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{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 182 - 修訂歷史

Ikk：新頁面: 檔案:SCJP182-2.jpg the class definitions: class Animal{} class Dog extends Animal{} and the code: public void go(){ ArrayList aList = new ArrayList();...