java程式設計師認證試題練習
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一.說明:(真實考試)
2.考題形式:多選,單選,簡答
3.題量:60
4.考試時間:120分鐘
二.模擬題
h statement about the garbage collection mechanism are true?
A. Garbage collection require additional programe code in cases where multiple threads are running.
B. The programmer can indicate that a reference through a local variable is no longer of interest.
C. The programmer has a mechanism that explicity and immediately frees the memory used by Java objects.
D. The garbage collection mechanism can free the memory used by Java Object at explection time.
E. The garbage collection system never reclaims memory from objects while are still accessible to running user threads.
2. Give the following method:
1) public void method( ){
2) String a,b;
3) a=new String(“hello world”);
4) b=new String(“game over”);
5) tln(a b ”ok”);
6) a=null;
7) a=b;
8) tln(a);
9) }
In the absence of compiler optimization, which is the earliest point the object a refered is definitely elibile to be garbage collection.
A. before line 3
re line 5
C. before line 6
re line 7
E. Before line 9
3. In the class vent,which is the parent class upon which jdk1.1 awt events are based there is a method called getID which phrase accurately describes the return value of this method?
A. It is a reference to the object directly affected by the cause of the event.
B. It is an indication of the nature of the cause of the event.
C. It is an indication of the position of the mouse when it caused the event.
D. In the case of a mouse click, it is an indication of the text under the mouse at the time of the event.
E. It tells the state of certain keys on the keybord at the time of the event.
F. It is an indication of the time at which the event occurred.
4. Which statement about listener is true?
A. Most component allow multiple listeners to be added.
B. If multiple listener be add to a single component, the event only affected one listener.
C. Component don?t allow multiple listeners to be add.
D. The listener mechanism allows you to call an addXxxxListener method as many times as is needed, specifying as many different listeners as your design require.
the following code:
public class Example{
public static void main(String args[] ){
int l=0;
do{
tln(“Doing it for l is:” l);
}while(--l>0)
tln(“Finish”);
}
}
Which well be output:
A. Doing it for l is 3
B. Doing it for l is 1
C. Doing it for l is 2
D. Doing it for l is 0
E. Doing it for l is ?C1
F. Finish見1-5題答案
答案及詳細分析：
1。B、E
JAVA的垃圾回收機制是通過一個後臺系統級執行緒對記憶體分配情況進行跟蹤實現的，對程式設計師來說是透明的，程式設計師沒有任何方式使無用記憶體顯示的、立即的被釋放。而且它是在程式執行期間發生的。
答案B告訴我們程式設計師可以使一個本地變數失去任何意義，例如給本地變數賦值為“null”;答案E告訴我們在程式執行期間不可能完全釋放記憶體。
2。D
第6行將null賦值給a以後，a以前儲存的引用所指向的記憶體空間就失去了作用，它可能被釋放。所以物件a可能最早被垃圾回收是在第7行以前，故選擇D選項。
3。B
請查閱JAVA類庫。getID方法的返回值是“event type”。在認證考試中，總會有類似的書本以外的知識，這隻能靠多實踐來增長知識了。
4。A、D
控制元件可以同時使用多個“addXxxxListener”方法加入多個監測器。並且當多個監測器加入到同一控制元件中時，事件可以響應多個監測器，響應是沒有固定順序的。
5。D、F
本題主要考察考生對流程控制的掌握情況。這是當型迴圈，條件為真執行，條件為假則退出。迴圈體至少執行一次，故會輸出D。迴圈體以外的語句總會被執行，故輸出F。
6. Give the code fragment:
1) switch(x){
2) case 1:tln(“Test 1”);break;
3) case 2:
4) case 3:tln(“Test 2”);break;
5) default:tln(“end”);
6) }
which value of x would cause “Test 2” to the output:
A. 1
B. 2
C. 3
D. default
7. Give incompleted method:
1)
2) { if(unsafe()){//do something…}
3) else if(safe()){//do the other…}
4) }
The method unsafe() well throe an IOException, which completes the method of declaration when added at line one?
A. public IOException methodName()
B. public void methodName()
C. public void methodName() throw IOException
D. public void methodName() throws IOException
E. public void methodName() throws Exception
8. Give the code fragment:
if(x>4){
tln(“Test 1”);}
else if (x>9){
tln(“Test 2”);}
else {
tln(“Test 3”);}
Which range of value x would produce of output “Test 2”?
A. x<4
B. x>4
C. x>9
D. None
9. Give the following method:
public void example(){
try{
unsafe();
tln(“Test1”);
}catch(SafeException e){tln(“Test 2”);
}finally{tln(“Test 3”);}
tln(“Test 4”);
Which will display if method unsafe () run normally?
A. Test 1
B. Test 2
C. Test 3
D. Test 4
10. Which method you define as the starting point of new thread in a class from which new the thread can be excution?
A. public void start()
B. public void run()
C. public void int()
D. public static void main(String args[])
E. public void runnable()
6-10答案:
6。B.C
在開關語句中，標號總是不被當做語句的一部分，標號的作用就是做為條件判斷而已，一旦匹配成功，就執行其後的語句，一直遭遇break語句為止。(包括default語句在內)
7。D、F
IOException異常類是Exception的子類。根據多型性的定義，IOException物件也可以被認為是Exception型別。還要注意在方法宣告中丟擲異常應用關鍵字“throws”。
8。D
只有兩種情況：大於4時輸出“Test1”，小於等於4時輸出“Test3”。
9。A、C、D
在正常情況下，列印Test1、Test3、Test4;在產生可捕獲異常時列印Test2、Test3、Test4;在產生不可捕獲異常時，列印Test3，然後終止程式。注意finally後面的語句總是被執行。
10。B
執行緒的執行是從方法“run( )”開始的，該方法是由系統呼叫的。程式設計師手工呼叫方法start()，使執行緒變為可執行狀態。
n the following class definition:
class A{
protected int i;
A(int i){
this.i=i;
}
}
which of the following would be a valid inner class for this class?
Select all valid answers:
A. class B{
}
B. class B extends A{
}
C. class B extends A{
B(){tln(“i=” i);}
}
D. class B{
class A{}
}
E. class A{}
12. Which modifier should be applied to a method for the lock of object this to be obtained prior to excution any of the method body?
A. synchronized
B. abstract
C. final
D. static
E. public
13. The following code is entire contents of a file called ,causes precisely one error during compilation:
1) class SubClass extends BaseClass{
2) }
3) class BaseClass(){
4) String str;
5) public BaseClass(){
6) tln(“ok”);}
7) public BaseClass(String s){
8) str=s;}}
9) public class Example{
10) public void method(){
11) SubClass s=new SubClass(“hello”);
12) BaseClass b=new BaseClass(“world”);
13) }
14) }
Which line would be cause the error?
A. 9 B. 10 C. 11 D.12
14. Which statement is correctly declare a variable a which is suitable for refering to an array of 50 string empty object?
A. String [] a
B. String a[]
C. char a[][]
D. String a[50]
F. Object a[50]
15. Give the following java source fragement:
//point x
public class Interesting{
//do something
}
Which statement is correctly Java syntax at point x?
A. import .*;
age mypackage
C. static int PI=3.14
D. public class MyClass{//do other thing…} E. class MyClass{//do something…}11-15答案：
11。A
此題考查內部類及關鍵字“super”的'用法。內部類不能與外部類同名。另外，當B繼承A時，A中的建構函式是帶引數的，B中預設建構函式的函式體為空;而JAVA編譯器會為空建構函式體自動新增語句“super();”呼叫父類建構函式，更進一步是呼叫父類的引數為空的建構函式。而父類中沒有引數為空的建構函式。
12。A
此關鍵字可以在兩個執行緒同時試圖訪問某一資料時避免資料毀損。
13。C
當一個類中未顯式定義建構函式時，預設的建構函式是以類名為函式名，引數為空，函式體為空。雖然父類中的某一建構函式有字串引數s，但是子類繼承父類時並不繼承建構函式，所以它只能使用預設建構函式。故在第11行出錯。
14。A、B
注意，題中問的是如何正確宣告一個一維陣列，並非例項化或者初始化陣列
15。A、E
X處可以是一個輸入，包的定義，類的定義。由於常量或變數的宣告只能在類中或方法中，故不能選擇C;由於在一個檔案中只能有一個public類，故不能選擇D。
16. Give this class outline:
class Example{
private int x;
//rest of class body…
}
Assuming that x invoked by the code java Example, which statement can made x be directly accessible in main() method of ?
A. Change private int x to public int x
B. change private int x to static int x
C. Change private int x to protected int x
D. change private int x to final int x
17. the piece of preliminary analsis work describes a class that will be used frequently in many unrelated parts of a project
“The polygon object is a drawable, A polygon has vertex information stored in a vector, a color, length and width.”
Which Data type would be used?
A. Vector
B. int
C. String
D. Color
E. Date
18. A class design requires that a member variable should be accessible only by same package, which modifer word should be used?
A. protected
B. public
C. no modifer
D. private
h declares for native method in a java class corrected?
A. public native void method(){}
B. public native void method();
C. public native method();
D. public void method(){native;}
E. public void native method();
20. Which modifer should be applied to a declaration of a class member variable for the value of variable to remain constant after the creation of the object?
16-20答安：
16。B
靜態方法除了自己的引數外只能直接訪問靜態成員。訪問非靜態成員，必須先例項化本類的一個例項，再用例項名點取。
17。A、B、D
polygon的頂點資訊存放在Vector型別的物件內部，color定義為Color，length和width定義為int。
注意，這是考試中常見的題型。
18。C
此題考點是高階訪問控制。請考生查閱高階訪問控制說明表格。
19。B
native關鍵字指明是對本地方法的呼叫，在JAVA中是隻能訪問但不能寫的方法，它的位置在訪問許可權修飾語的後面及返回值的前面。
20。final
定義常量的方法是在變數定義前加final關鍵字。
21. Which is the main() method return of a application?
A. String
B. byte
C. char
D. void
22. Which is corrected argument of main() method of application?
A. String args
B. String ar[]
C. Char args[][]
D. StringBuffer arg[]
23. “The Employee object is a person, An Employee has appointment store in a vector, a hire date and a number of dependent”
short answer: use shortest statement declare a class of Employee.
24. Give the following class defination inseparate source files:
public class Example{
public Example(){//do something}
protected Example(int i){//do something}
protected void method(){//do something}
}
public class Hello extends Example{//member method and member variable}
Which methods are corrected added to the class Hello?
A. public void Example(){}
B. public void method(){}
C. protected void method(){}
D. private void method(){}
25. Float s=new Float(0.9F);
Float t=new Float(0.9F);
Double u=new Double(0.9);
Which expression?s result is true?
A. s==t
B. ls(t)
C. s==u
D. ls(u)
21-15答案：
21。D
main()方法沒有返回值，所以必須用void修飾。main()方法的返回值不能任意修改。
22。B
main()方法的引數是字串陣列，引數名可以任意定義。
23。public class Employee extends Person
這也是真實考試中常見的一種題型。要注意題目敘述中“is a”表示 “extends”的含義。
24。A、B、C
考察的知識點是方法覆蓋，其中要注意的是方法覆蓋時，子類方法的訪問許可權不能小於父類方法的訪問許可權。另外，選項A並不是父類建構函式，它是子類中的新方法。
25。A、B
考察“==”及方法“equals()”的用法。注意以下幾點區別：
1) 引用型別比較引用;基本型別比較值。
2) equals()方法只能比較引用型別，“==”可比較引用及基本型別。
3) 當用equals()方法進行比較時，對類File、String、Date及封裝類(Wrapper Class)來說，是比較型別及內容。
4) 用“==”進行比較時，符號兩邊的資料型別必須一致(可相互轉換的基本型別除外)，否則編譯出錯。
