java认证考试试卷_java认证考试试题及答案

java认证考试试卷_java认证考试试题及答案java认证考试试题及答案故答案为C。12.Whatistheresultafterthefollowingcodeexecutes?1shorts=0x00FD;2byteb=(byte)s;3System.out.println(b);Select1correctanswer:A.Compiletimeerrorinline1B.Comp…

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java认证考试试题及答案

故答案为C。

12. What is the result after the following code executes?

1 short s = 0x00FD;

2 byte b = (byte)s;

3 System.out.println(b);

Select 1 correct answer:

A. Compile time error in line 1

B. Compile time error in line 2

C. 0

D. -3

E. -2

解析:考察对强制类型转换的理解,java中,short类型为16位,占据两个字节,byte类型为八位。第二行,对s进行了强制类型转换,而这实际上是一个收缩基本转换,从带符号整数到整型T的收索转换只是简单地丢弃除n个最低阶位以外的其它所有位,这可能导致数目或者符号的变化。

Java中所有的整数类型都具有符号位,故需要考虑二进制表示

b=0xFD=1111 1101,是一个补码。

将最高位为1的补码转换为原码的步骤为(最高位为0的补码和原码相同)先将补码全部取反,然后+1

b取反后得到0000 0010,加1 : 0000 0011,即3,考虑到这是一个附负数,最后的结果为-3

答案:D

13. Given the following method in an application:

1. public String setFileType( String fname ){

2. int p = fname.indexOf( ‘.’ );

3. if( p > 0 ) fname = fname.substring( 0,p );

4. fname += “.TXT”;

5. return fname;

6. }

and given that another part of the class has the following code:

7. String TheFile = “Program.java”;

8. File F = new File( setFileType( TheFile ) );

9. System.out.println( “Created ” + TheFile );

what will be printed by the statement in line 9?

Select 1 correct answer:

A. Created Program.java

B. Created Program.txt

C. Created Program.java.txt

答案:A

14. Here is the ActionEvent family tree:

java.lang.Object

|— java.util.EventObject

|— java.awt.AWTEvent

|—- java.awt.event.ActionEvent

Suppose we have the following code to count events and

save the most recent event:

int evtCt = 0 ;

AWTEvent lastE ;

public void saveEvent( AWTEvent evt )

{

lastE = evt ;

evtCt++ ;

}

Which of the following calls of saveEvent would run

without causing an exception?

Select all possible answers:

A. call with an AWTEvent object reference

B. call with an ActionEvent object reference

C. call with an EventObject object reference

D. call with null value

答案:ABD

15. Suppose we have two classes defined as follows:

class ApBase extends Object implements Runnable

class ApDerived extends ApBase implements Observer

Given two variables created as follows:

ApBase aBase = new ApBase() ;

ApDerived aDer = new ApDerived();

Which of the following Java code fragments will

compile and execute without error?

Select 1 correct answer:

A. Object obj = aBase ; Runnable rn = obj ;

B. Object obj = aBase ; Runnable rn = (Runnable) obj ;

C. Object obj = aBase ; Observer ob = (Observer)aBase ;

D. Object obj = aDer ; Observer ob2 = obj ;

答案:B?

16. The following lists the complete contents

of the file named Derived.java:

1. public class Base extends Object {

2. String objType ;

3. public Base(){ objType = “I am a Base type” ;

4. }

5. }

6.

7. public class Derived extends Base {

8. public Derived() { objType = “I am a Derived type”;

9. }

10. public static void main(String args[] ){

11. Derived D = new Derived();

12. }

13. }

What will happen when this file is compiled?

Select 1 correct answer:

A. Two class files, Base.class and Derived.class will be created

B. The compiler will object to line 1

C. The compiler will object to line 7

解析:

答案:B

17. The following method is designed to convert an input string

to a floating point number, while detecting a bad format.

Assume that factor is correctly defined elsewhere:

public boolean strCvt( String s ){

try {

factor = Double.valueOf( s ).doubleValue();

return true ;

} catch(NumberFormatException e){

System.out.println(“Bad number ” + s );

factor = Double.NaN ;

}finally { System.out.println(“Finally”);

}

return false ; }

Which of the following descriptions of the results of various

inputs to the method are correct? Select all possible answers:

A. Input = “0.234”

Result:factor = 0.234, “Finally” is printed, true is returned.

B. Input = “0.234”

Result:factor = 0.234, “Finally” is printed, false is returned.

C. Input = null

Result:factor = NaN, “Finally” is printed, false is returned.

D. Input = null

Result:factor unchanged,”Finally” is printed,

NullPointerException is thrown.

解析:finally无论在什么情况下都会执行。

对于double.valueof,当输入为null(注意,不是字符串null,字符串null仍然会导致NumberFormatException)时,会导致NullPointerException

答案:A D

18. Here is the hierarchy of Exceptions related to

array index errors:

Exception

+– RuntimeException

+– IndexOutOfBoundsException

+– ArrayIndexOutOfBoundsException

+– StringIndexOutOfBoundsException

Suppose you had a method X which could throw both

array index and string index exceptions. Assuming

that X does not have any try – catch statements,

which of the following statements are correct?

A. The declaration for X must include

“throws ArrayIndexOutOfBoundsException,

StringIndexOutOfBoundsException”.

B. If a method calling X catches IndexOutOfBoundsException, both

array and string index exceptions will be caught.

C. If the declaration for X includes “throwsIndexOutOfBoundsException”,

any calling method must use a try – catch block.

D. The declaration for X does not have to mention exceptions.

解析:RuntimeException是运行时异常,属于不可查异常,程序无需声明,也无需处理。

答案:BD

19. Given the following listing of the Widget class:

1 class Widget extends Thingee{

2 static private int widgetCount = 0 ;

3 public String wName ;

4 int wNumber ;

5

6 static synchronized int addWidget(){ widgetCount++ ;

7 wName = “I am Widget # ” + widgetCount ;

8 return widgetCount ;

9 }

10 public Widget(){

11 wNumber = addWidget();

12 }

13 }

What happens when we try to compile the class and use

multiple Widget objects in a program?

Select 1 correct answer:

A. The class compiles and each Widget will get a unique wNumber

and wName reflecting the order in which the Widgets were created.

B. The compiler objects to line 7

C. A runtime error occurs in the addWidget method

答案:B 原因:静态方法操作的必须是静态变量

20. Given the following class definition:

public class DerivedDemo extends Demo

{

int M, N, L ;

public DerivedDemo( int x, int y )

{

M = x ; N = y ;

}

public DerivedDemo( int x )

{

super( x );

}

}

Which of the following constructor signatures MUST exist

in the Demo class for DerivedDemo to compile correctly?

Select 2 correct answers:

A. public Demo( int a, int b )

B. public Demo( int c )

C. public Demo( )

答案:B C

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