11.Given the following class definition:

class A{

protected int i;

A(int i){

this.i=i;

}

}

which of the following would be a valid inner class for this class?

Select all valid answers:

A. class B{

}

B. class B extends A{

}

C. class B extends A{

B(){System.out.println(“i=”+i);}

}

D. class B{

class A{}

}

E. class A{}

11。A

此題考查內(nèi)部類(lèi)及關(guān)鍵字“super”的用法。內(nèi)部類(lèi)不能與外部類(lèi)同名。另外，當(dāng)Ｂ繼承Ａ?xí)r，Ａ中的構(gòu)造函數(shù)是帶參數(shù)的，Ｂ中缺省構(gòu)造函數(shù)的函數(shù)體為空；而ＪＡＶＡ編譯器會(huì)為空構(gòu)造函數(shù)體自動(dòng)添加語(yǔ)句“super();”調(diào)用父類(lèi)構(gòu)造函數(shù)，更進(jìn)一步是調(diào)用父類(lèi)的參數(shù)為空的構(gòu)造函數(shù)。而父類(lèi)中沒(méi)有參數(shù)為空的構(gòu)造函數(shù)。

12. Which modifier should be applied to a method for the lock of object this to be obtained prior to excution any of the method body?

A. synchronized

B. abstract

C. final

D. static

E. public

12。A

此關(guān)鍵字可以在兩個(gè)線(xiàn)程同時(shí)試圖訪(fǎng)問(wèn)某一數(shù)據(jù)時(shí)避免數(shù)據(jù)毀損。

13. The following code is entire contents of a file called Example.java,causes precisely one error during compilation:

1) class SubClass extends BaseClass{

2) }

3) class BaseClass(){

4) String str;

5) public BaseClass(){

6) System.out.println(“ok”);}

7) public BaseClass(String s){

8) str=s;}}

9) public class Example{

10) public void method(){

11) SubClass s=new SubClass(“hello”);

12) BaseClass b=new BaseClass(“world”);

13) }

14) }

Which line would be cause the error?

A. 9 B. 10 C. 11 D.12

13。C

當(dāng)一個(gè)類(lèi)中未顯式定義構(gòu)造函數(shù)時(shí)，缺省的構(gòu)造函數(shù)是以類(lèi)名為函數(shù)名，參數(shù)為空，函數(shù)體為空。雖然父類(lèi)中的某一構(gòu)造函數(shù)有字符串參數(shù)s，但是子類(lèi)繼承父類(lèi)時(shí)并不繼承構(gòu)造函數(shù)，所以它只能使用缺省構(gòu)造函數(shù)。故在第11行出錯(cuò)。

14. Which statement is correctly declare a variable a which is suitable for refering to an array of 50 string empty object?

A. String [] a

B. String a[]

C. char a[][]

D. String a[50]

F. Object a[50]

14。A、B

注意，題中問(wèn)的是如何正確聲明一個(gè)一維數(shù)組，并非實(shí)例化或者初始化數(shù)組

15. Give the following java source fragement:

//point x

public class Interesting{

//do something

}

Which statement is correctly Java syntax at point x?

A. import java.awt.*;

B.package mypackage

C. static int PI=3.14

D. public class MyClass{//do other thing…} E. class MyClass{//do something…}

15。A、E

X處可以是一個(gè)輸入，包的定義，類(lèi)的定義。由于常量或變量的聲明只能在類(lèi)中或方法中，故不能選擇C；由于在一個(gè)文件中只能有一個(gè)public類(lèi)，故不能選擇D。

16. Give this class outline:

class Example{

private int x;

//rest of class body…

}

Assuming that x invoked by the code java Example, which statement can made x be directly accessible in main() method of Example.java?

A. Change private int x to public int x

B. change private int x to static int x

C. Change private int x to protected int x

D. change private int x to final int x

16。B

靜態(tài)方法除了自己的參數(shù)外只能直接訪(fǎng)問(wèn)靜態(tài)成員。訪(fǎng)問(wèn)非靜態(tài)成員，必須先實(shí)例化本類(lèi)的一個(gè)實(shí)例，再用實(shí)例名點(diǎn)取。

17. the piece of preliminary analsis work describes a class that will be used frequently in many unrelated parts of a project

“The polygon object is a drawable, A polygon has vertex information stored in a vector, a color, length and width.”

Which Data type would be used?

A. Vector

B. int

C. String

D. Color

E. Date

17。A、B、D

polygon的頂點(diǎn)信息存放在Vector類(lèi)型的對(duì)象內(nèi)部，color定義為Color，length和width定義為int。

注意，這是考試中常見(jiàn)的題型。

18. A class design requires that a member variable should be accessible only by same package, which modifer word should be used?

A. protected

B. public

C. no modifer

D. private

18。C

此題考點(diǎn)是高級(jí)訪(fǎng)問(wèn)控制。請(qǐng)考生查閱高級(jí)訪(fǎng)問(wèn)控制說(shuō)明表格。

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