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Sun java认证考试真题答案
SUN认证是给网络设计界建立的一套认证标准，Sun公司推出了Java以及Solaris技术认证方案。以下是小编整理的关于Sun java认证考试真题答案，希望大家认真阅读!
1. What gets printed when the following program
is compiled and run?
class Test {
public static void main(String args[]) {
int i;
do {
i++;
} while (i < 0);
System.out.println(i);
}
}
Select 1 correct answer:
A. The program does not compile as i is not initialized.
B. The program compiles but does not run.
C. The program compiles and runs but does not print anything.
D. The program prints 0.
E. The program prints 1.
答案：A：如果没有初始化便使用基本变量类型，会导致编译时异常，程序不能编译。
2. What gets printed when the following program
is compiled and run?
public class XYZ {
public static void main(String args[]) {
int i,j,k;
for (i = 0; i < 3; i++)
{
for(j=1; j < 4; j++)
{
for(k=2; k<5; k++)
{
if((i == j) && (j==k))
System.out.println(i);
} } } } }
Select 1 correct answer:
A. 0
B. 1
C. 2
D. 3
E. 4
答案：C
3. Given the following code :
class Base{}
public class MyCast extends Base{
static boolean b1=false;
static int i = -1;
static double d = 10.1;
public static void main(String argv[]){
MyCast m = new MyCast();
Base b = new Base();
//Here
}
}
Which of the following, if ed at the comment //Here
will allow the code to compile and run without error?
Select 2 correct answers:
A. b = m;
B. m = b;
C. d = i;
D. b1 = i;
解析：A 从子类型到父类型的转换是扩展引用转换，不需要在运行时采取特殊的动作，不会在运行时抛出异常。
B 从超类型到子类型的转换是收缩引用转换，需要在运行时执行测试，以查明实际的引用值是否是新类型的合法值.如果不是， 则会抛出ClassCascException 。在这里，b本身不是MyCast类型的值，因此会导致运行时异常。
C 从int到double的转换是扩展基本转换，基本类型之间的扩展转换永远不会导致运行时异常。但从int或long到float，或者是从long到double都可能导致精度丢失。
D 不允许进行int和boolean之间的类型转换
答案：A、C
4. Given the following classes which of the following
will compile without error?
interface IFace{}
class CFace implements IFace{}
class Base{}
public class ObRef extends Base{
public static void main(String argv[])
{
ObRef ob = new ObRef();
Base b = new Base();
Object o1 = new Object();
IFace o2 = new CFace();
}
}
Select 3 correct answers:
A. o1 = o2;
B. b = ob;
C. ob = b;
D. o1 = b;
解析：A 任何对象都可以赋给Object类型的对象，正确
B 子类赋给超类是扩展引用转换，可以进行
C 收缩引用转换，错误
D 扩展引用转换，可以进行
答案 A B D
5. What is the result of compiling and running the following code?
1 public class Test {
2 static int total = 10;
3 public static void main (String args []) {
4 new Test();
5 }
6 public Test () {
7 System.out.println("In test");
8 System.out.println(this);
9 int temp = this.total;
10 if (temp > 5) {
11 System.out.println(temp);
12 }
13 }
14 }
Select 1 correct answer:
A. The class will not compile
B. The compiler reports an error at line 2
C. The compiler reports an error at line 9
D. The value 10 is one of the printed elements
E. The class compiles but generates a runtime error
答案：D 由于test类没有override toString方法，故在调用println(this)时会直接显示类的有关信息。
6. Carefully examine the following code:
public class StaticTest {
static { System.out.println("Hi there"); }
public void print() {
System.out.println("Hello");
}
public static void main(String args []) {
StaticTest st1 = new StaticTest();
st1.print();
StaticTest st2 = new StaticTest();
st2.print();
}}
When will the string "Hi there" be printed?
Select 1 correct answer:
A. Never
B. Each time a new instance is created
C. Once, when the class is first loaded into the JVM
D. Only when the static method is called explicitly
答案 C
Java虚拟机规范约定，类的初始化发生在首次主动使用时。静态变量和静态初始化块的先后，实际上取决于它们在类中出现的先后顺序。
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