Sun java认证考试真题答案及部分解析（三）

41. What will be the output of the following code?

public class Test

{ 

public static String output="";

public static void foo(int i)

{

try

{

if(i==1)

{

throw new Exception();

}

output +="1";

}

catch(Exception e)

{

output+="2";

return;

}

finally

{

output+="3";

}

output+="4";

}

public static void main(String args[])

{

foo(0);

System.out.print(output + " ");

foo(1);

System.out.println(output);

}

}

Select 1 correct answer:

A. 134 134234 

B. 13 123

C. 134 13423

D. 14 13423

答案：C

42. What will be the output of the following code?

public class Test

{ 

public static void main(String args[])

{

int i=1,j=10;

do{

if(i++>--j) continue;

}while(i<5);

System.out.println(i +" " +j);

}

}

Select 1 correct answer:

A. i=6 j=5 

B. i=5 j=5 

C. i=6 j=4 

D. i=5 j=6 

E. i=6 j=6

答案：D

43. What will be the output of the following code?

interface Foo{

int k=0;

}

public class Test implements Foo{

public static void main(String args[]){

Test test =new Test();

System.out.print(test.k + " ");

System.out.print(Test.k + " ");

System.out.println(Foo.k);

}

}

Select 1 correct answer:

A. 0 0 0

B. A runtime exception is thrown.

C. The code does not compile.

解析：考察对接口的理解：接口中所有的变量都是public static final，并且不允许没有初始值。

答案：A

44. What will be the output of the following code?

class Dum

{

private int f = 5;

public void setF(int f)

{

this.f = f;

}

public int getF()

{

return f;

}

}

public class Test{

public static void change(Dum d)

{

d.setF(4581);

}

public static void main(String args[]){

Dum dd = new Dum();

System.out.print(dd.getF() + " ");

change(dd);

System.out.println(dd.getF());

}

}

Select 1 correct answer: 

A. 5 5

B. The code will not compile.

C. Runtime exception will be thrown.

D. 5 4581

答案：D

45. What will be the output of the following code?

public class Test{

public static void add3(Integer i){

int val=i.intValue();

val+=3;

i=new Integer(val);

}

public static void main(String args[]){

Integer i=new Integer(0);

add3(i);

System.out.println(i.intValue());

}

}

Select 1 correct answer: 

A. The code will not compile. 

B. 0 

C. 3 

D. A runtime exception will be thrown.

答案：B

46. What will be the output of the following code?

public class Test{

public static void stringReplace(String text){

text=text.replace('j','l');

}

public static void bufferReplace(StringBuffer text){

text=text.append("c");

}

public static void main(String args[]){

String textString=new String("java");

StringBuffer textBuffer=new StringBuffer("java");

stringReplace(textString);

bufferReplace(textBuffer);

System.out.println(textString + " " + textBuffer);

}}

Select 1 correct answer: 

A. lava javac

B. lava java

C. java javac

D. The code will not compile.

解析：string是不可变的，故会产生新的引用，但这一引用并不能通过stringReplace反映到外面的text变量上，而StringBuilder是可变的， 对其的改变会改变自己，同时返回自己的引用。

答案：C

47. Given the following code:

class EnclosingOne{

public class InsideOne{}

}

public class InnerTest{

public static void main(String args[]){

EnclosingOne eo=new EnclosingOne();

//insert code here

}

}

Which of the next statements can be placed 

legally in place of //insert code here?

Select all correct answers: 

A. InsideOne ei=eo.new InsideOne();

B. eo.InsideOne ei=eo.new InsideOne();

C. InsideOne ei=EnclosingOne.new InsideOne();

D. InsideOne ei=eo.new InsideOne();

E. EnclosingOne.InsideOne ei=eo.new InsideOne();

解析：考察对嵌套类的操作方法

答案：E

48. Given the following code:

import java.awt.*;

public class Test extends Frame{

public static void main(String[] args){

Test x=new Test();

x.pack();

x.setVisible(true);}

public Test(){

setLayout(new GridLayout(2,2));

Panel p1=new Panel();

add(p1);

Button b1=new Button("One");

p1.add(b1);

Panel p2=new Panel();

add(p2);

Button b2=new Button("Two");

p2.add(b2);

Button b3=new Button("Three");

p2.add(b3);

Button b4=new Button("Four");

add(b4);

}}

What will happen when the frame is resized?

Select all correct answers:

A. All buttons' height is changed. 

B. All buttons' width is changed. 

C. The height of button "One" is changed.

D. The height of button "Two" is changed.

E. The width of button "Four" is changed.

F. Both the width and the height of button "Four" are changed.

答案：EF

49. Which four types of objects can be thrown using "throws"?

A. Error

B. Event

C. Object

D. Exception

E. Throwable

F. RuntimeException

答案：A D E F

50. What will be the output of the following code?

1 public class X {

2 public static void main(String[] args) {

3 int[] a=new int[1];

4 modify(a);

5 System.out.println(a[0]);

6 }

7 public static void modify(int[] a){

8 a[0]++;}

9 }

Select 1 correct answer:

A. The program runs and prints 0.

B. The program runs and prints 1.

C. The program runs but aborts with an exception.

D. An error "possible undefined variable" at line 4 

   causes compilation to fail;

E. An error "possible undefined variable" at line 8 

   causes compilation to fail;

答案：B

51. What will be the result of trying to compile

    and run the following code?

1 public class X {

2 public static void main(String[] args) {

3 byte b = 127;

4 byte c = 126;

5 byte d = b+c;

6 }

7 }

Select 1 correct answer:

A. The code compiles but line 5 throws a runtime exception.

B. Line 5 fails to compile.

C. Successful compilation.

答案：B 原因在于，数值提升仅允许使用同一性转换，扩展基本转换或拆箱转换，而不允许使用收缩基本转换。而且，在进行二元运算时，会进行数值提升，至少提升到int。

52. What happens when we attempt to compile and 

    run the following code?

1. public class Logic {

2. static long sixteen = 0x0010;

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

4. long N = sixteen >> 4;

5. System.out.println( "N = " + N );

6. }

7. }

Select 1 correct answer:

A. The compiler will object to line 4 combining a long with an int.

B. The program will compile and run, producing the output "N = 0".

C. The program will compile and run, producing the output "N = 1".

D. A runtime exception will be thrown.

答案：C

53. What will be the output?

public class Test {

public static void main( String[] args ) {

int i = 1;

int j = i++;

if( ( i > ++j ) && ( i++ == j ) ) {

i += j;

}

System.out.println( i + " " + j );

}

}

Select 1 correct answer:

A. 2 1

B. 1 1

C. 2 2

D. 1 2

解析：&&为短路与，如果第一个为false，则不再继续运算

答案：C

54. Which statement is true for the class java.util.HashSet?

Select all correct answers:

A. The elements in the collection are ordered.

B. The collection is guaranteeded to be immutable.

C. The elements in the collection are guaranteed to be unique.

D. The elements in the collection are accessed using a unique key.

E. The elements in the collection are guaranteed to be synchronized.

答案：D

注意：HashSet不是同步的。

55. What will be the output of the following code?

public class Test

{

public static void main( String []args ) {

StringBuffer a = new StringBuffer("A");

StringBuffer b = new StringBuffer("B");

operate( a,b );

System.out.println( a + "," + b );

}

public static void operate( StringBuffer x, StringBuffer y ) {

x.append( y );

y = x;

}

}

Select 1 correct answer:

A. A, B

B. The code will not compile.

C. B, A

D. AB, B

答案：D

56. What will be the output of the following code?

public class Test

{

public static void main(String[] args) {

class Foo

{

public int i=3;

}

Object o = (Object)new Foo();

Foo foo = (Foo)o;

System.out.println( foo.i );

}

}

Select 1 correct answer:

A. Compile time error.

B. Run time error.

C. 3

答案：C

57. Given the following code fragment, what will happen 

    when we try to compile and run the showSmall method?

1. public void printArray( long[] x ){

2. for(int i = 0 ; i < x.length ; i++ ){

3. System.out.println("# " + i + " = " + x[i] );

4. }

5. }

6. int[] small = { 1,2,3,4,5,6,7,8,9,0 };

7. public void showSmall() {

8. printArray( small );

9. }

Select 1 correct answer:

A. The code compiles and the JVM automatically promotes 

   the int array to a long array.

B. The compiler complains that there is no method matching

   the use in line 8.

C. The code compiles but a runtime ClassCastException 

   is thrown in line 8.

解析：考察对类型提升的理解：JVM不能自动将int数组提升为long数组。

答案：B

58. What will be the output of the following program? 

class A implements Runnable {

public int i = 1;

public void run() {

System.out.println("in run");

this.i = 10;

System.out.println(i);

}

}

public class Test {

public static void main(String args[]) {

A a = new A();

new Thread(a).start();

int j = a.i;

System.out.println(j);

}

}

Select 1 correct answer:

A. 1

B. 10

C. The code compiles but a runtime is thrown.

D. The program runs but the exact output cannot be determined.

答案：D

59. What happens on trying to compile and run the following code?

1. public class EqualsTest{

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

3. float A = 1.0F / 3.0F ;

4. if( ( A * 3.0) == 1.0F )

       System.out.println( "Equal" );

5. else System.out.println( "Not Equal" );

6. }

7. }

Select 1 correct answer:

A. The program compiles and prints "Not Equal".

B. The program compiles and prints "Equal".

C. The compiler objects to line 3.

D. The compiler objects to using == with primitives in line 4.

答案：A