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Sun java認(rèn)證考試答案
SUN認(rèn)證是給網(wǎng)絡(luò)設(shè)計界建立的一套認(rèn)證標(biāo)準(zhǔn)，Sun公司推出了Java以及Solaris技術(shù)認(rèn)證方案。小編收集一些Sun java認(rèn)證考試真題答案，希望發(fā)夾認(rèn)真做題!
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：如果沒有初始化便使用基本變量類型，會導(dǎo)致編譯時異常，程序不能編譯。
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 inserted 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 從子類型到父類型的轉(zhuǎn)換是擴(kuò)展引用轉(zhuǎn)換，不需要在運(yùn)行時采取特殊的動作，不會在運(yùn)行時拋出異常。
B 從超類型到子類型的轉(zhuǎn)換是收縮引用轉(zhuǎn)換，需要在運(yùn)行時執(zhí)行測試，以查明實際的引用值是否是新類型的合法值.如果不是， 則會拋出ClassCascException 。在這里，b本身不是MyCast類型的值，因此會導(dǎo)致運(yùn)行時異常。
C 從int到double的轉(zhuǎn)換是擴(kuò)展基本轉(zhuǎn)換，基本類型之間的擴(kuò)展轉(zhuǎn)換永遠(yuǎn)不會導(dǎo)致運(yùn)行時異常。但從int或long到float，或者是從long到double都可能導(dǎo)致精度丟失。
D 不允許進(jìn)行int和boolean之間的類型轉(zhuǎn)換
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 任何對象都可以賦給Object類型的對象，正確
B 子類賦給超類是擴(kuò)展引用轉(zhuǎn)換，可以進(jìn)行
C 收縮引用轉(zhuǎn)換，錯誤
D 擴(kuò)展引用轉(zhuǎn)換，可以進(jìn)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類沒有override toString方法，故在調(diào)用println(this)時會直接顯示類的有關(guān)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虛擬機(jī)規(guī)范約定，類的初始化發(fā)生在首次主動使用時。靜態(tài)變量和靜態(tài)初始化塊的先后，實際上取決于它們在類中出現(xiàn)的先后順序。
7. Given the following code what is the effect of a being 5?
public class Test {
public void add(int a) {
loop: for (int i = 1; i < 3; i++){
for (int j = 1; j < 3; j++) {
if (a == 5) {
break loop;
}
System.out.println(i * j);
}
}
}
}
Select 1 correct answer:
A. Generates a runtime error
B. Throws an ArrayIndexOutOfBoundsException
C. Prints the values: 1, 2, 2, 4
D. Produces no output
解析：考察標(biāo)記和break的使用。單純使用break只跳出當(dāng)前循環(huán)(一層)。如果在要跳出的循環(huán)前加標(biāo)記，那么在加過標(biāo)記的循環(huán)中的任何地方都可以使用break 標(biāo)記 來跳出該循環(huán)
答案：D
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