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SUN國(guó)際認(rèn)證試題及答案
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1.Which of the following fragments might cause errors?
A. String s = "Gone with the wind";
String t = " good ";
String k = s + t;
B. String s = "Gone with the wind";
String t;
t = s[3] + "one";
C. String s = "Gone with the wind";
String standard = s.toUpperCase();
D. String s = "home directory";
String t = s - "directory";
answer：(BD)這道題考察java字符串和連接符+的理解，B中s[3]是一個(gè)字符，而不能和一個(gè)字符串用連接符連起來(lái)。而D則是我們初學(xué)java時(shí)以為有+必定有-，所以導(dǎo)致錯(cuò)誤。java中的連接符只有一個(gè)就是+。而且字符串和字符是兩個(gè)不同的概念，我們要區(qū)分開(kāi)來(lái)。
2. Given the following code fragment:
1) public void create() {
2) Vector myVect;
3) myVect = new Vector();
4) }
Which of the following statements are true?
A. The declaration on line 2 does not allocate memory space for the variable myVect.
B. The declaration on line 2 allocates memory space for a reference to a Vector object.
C. The statement on line 2 creates an object of class Vector.
D. The statement on line 3 creates an object of class Vector.
E. The statement on line 3 allocates memory space for an object of class Vector
answer:(ADE)這題考察獲得實(shí)例的內(nèi)存變化。定義一個(gè)實(shí)例并不能給對(duì)象分配內(nèi)存空間，系統(tǒng)只給定義的那個(gè)變量分配空間。只有當(dāng)new 出一個(gè)對(duì)象時(shí)系統(tǒng)回給一個(gè)實(shí)例對(duì)象分配內(nèi)存空間。
3. Which are not Java keywords?
A. TRUE
B. sizeof
C. const
D. super
E. void
answer：(AB)sizeof是c++語(yǔ)言的的關(guān)鍵字，不是java的，我做題的時(shí)候覺(jué)得sizeof很熟悉，想當(dāng)然以為它就是java的關(guān)鍵字，結(jié)果可想而知。
4. Which are not Java primitive(基本) types?
A. short
B. Boolean
C. unit
D. float
answer：(BC)java基本數(shù)據(jù)類型只有8個(gè)，而B(niǎo)oolean是引用數(shù)據(jù)類型。選錯(cuò)了，關(guān)鍵是沒(méi)弄清primitive是什么意思，汗顏啊，英語(yǔ)太差了。
5. Which statements about the garbage collection are true?
A. The program developer must create a thread to be responsible for free
the memory.
B. The garbage collection will check for and free memory no longer needed.
C. The garbage collection allow the program developer to explicity and
immediately free the memory.
D. The garbage collection can free the memory used java object at expect
time.
answer：(B)java垃圾自動(dòng)回收機(jī)制，我們不能讓虛擬機(jī)什么時(shí)候開(kāi)始垃圾回收，垃圾回收是不受我們控制的，就算我們想要快點(diǎn)垃圾回收，我們只能通過(guò)一個(gè)gc()函數(shù)希望快點(diǎn)垃圾回收，但是程序回不回提前垃圾回收還是不知道的。所以選b。
6、Which of the following assignment is not correct?
A. float f = 11.1;
B. double d = 5.3E12;
C. double d = 3.14159;
D. double d = 3.14D.
answer：(A)記住基本數(shù)據(jù)類型中int和double都是默認(rèn)的，所以a是錯(cuò)的，把double轉(zhuǎn)換成float型要強(qiáng)制類型轉(zhuǎn)換。第一次碰到這樣的題的時(shí)候我全錯(cuò)，不過(guò)現(xiàn)在好了。
7、Given the uncompleted code of a class:
class Person {
String name, department;
int age;
public Person(String n){ name = n; }
public Person(String n, int a){ name = n; age = a; }
public Person(String n, String d, int a) {
// doing the same as two arguments version of constructor
// including assignment name=n,age=a
department = d;
}
}
Which expression can be added at the "doing the same as..." part of the constructor?
A. Person(n,a);
B. this(Person(n,a));
C. this(n,a);
D. this(name,age).
answer:(C)這題有較大迷惑，要是不認(rèn)真看，估計(jì)會(huì)選d，看看參數(shù)列表是n和a，如果選擇d的話就錯(cuò)了。
8、public void test() {
try { oneMethod();
System.out.println("condition 1");
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println("condition 2");
} catch(Exception e) {
System.out.println("condition 3");
} finally {
System.out.println("finally");
}
}
Which will display if oneMethod run normally?
A. condition 1
B. condition 2
C. condition 3
D. finally
answer：(AD)finally 修飾的最終都將會(huì)運(yùn)行，所以當(dāng)程序正常運(yùn)行，不拋出異常時(shí)，AD都將運(yùn)行。
9 Given the following code fragment:
1) String str = null;
2) if ((str != null) && (str.length() > 10)) {
3) System.out.println("more than 10");
4) }
5) else if ((str != null) & (str.length() < 5)) {
6) System.out.println("less than 5");
7) }
8) else { System.out.println("end"); }
Which line will cause error?
A. line 1
B. line 2
C. line 5
D. line 8
answer：(C)&&和&的區(qū)別，&是按位與計(jì)算，&兩邊的運(yùn)算都要執(zhí)行;&&是邏輯運(yùn)算，當(dāng)左邊為假時(shí)，右邊可以不執(zhí)行。當(dāng)右邊執(zhí)行時(shí)，可能有 (str.length()空指針異常)。
10、Given the following code:
public class Person{
static int arr[] = new int[10];
public static void main(String a[]) {
System.out.println(arr[1]) ;
}
}
Which statement is correct?
A. When compilation some error will occur.
B. It is correct when compilation but will cause error when running.
C. The output is zero.
D. The output is null.
answer：(C)java數(shù)組默認(rèn)初始化都為0.
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