java程序員認證模擬試題及解析
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Java程序員認證模擬題及詳細分析(1)
26. Give following class:
class AClass{
private long val;
public AClass(long v){val=v;}
public static void main(String args[]){
AClass x=new AClass(10L);
AClass y=new AClass(10L);
AClass z=y;
long a=10L;
int b=10;
}
}
Which expression result is true?
A. a==b;
B. a==x;
C. y==z;
D. x==y;
E. a==10.0;
27. A socket object has been created and connected to a standard internet service on a remote network server. Which construction give the most suitable means for reading ASCII data online at a time from the socket?
A. InputStream in=s.getInputStream();
B. DataInputStream in=new DataInputstream(s.getInputStream());
C. ByteArrayInputStream in=new ByteArrayInputStream(s.getInputStream());
D. BufferedReader in=new BufferedReader(new InputStreamReader(s.getInputStream()));
E. BufferedReader in=new BufferedReader(new InputStreamReader(s.getInputStream()),”8859-1”);
28. String s=”Example String”;
Which operation is legal?
A. s>>>=3;
B. int i=s.length();
C. s[3]=”x”;
D. String short_s=s.trim();
E. String t=”root” s;
29. What happens when you try to compile and run the following program?
class Mystery{
String s;
public static void main(String[] args){
Mystery m=new Mystery();
m.go();
}
void Mystery(){
s=”constructor”;
}
void go(){
System.out.println(s);
}
}
A. this code will not compile
B. this code compliles but throws an exception at runtime
C. this code runs but nothing appears in the standard output
D. this code runs and “constructor” in the standard output
E. this code runs and writes ”null” in the standard output 30. What use to position a Button in a Frame ,only width of Button is affected by the Frame size, which Layout Button well be set ?
A. FlowLayout;
B. GridLayout;
C. North of BorderLayout
D. South of BorderLayout
E. East or West of BorderLayout
31. What use to position a Button in a Frame, size of Button is not affected by the Frame size, which Layout Button will be set?
A. FlowLayout;
B. GridLayout;
C. North of BorderLayout
D. South of BorderLayout
E. East or West of BorderLayout
32. An AWT GUI under exposure condition, which one or more method well be invoke when it redraw?
A. paint();
B. update();
C. repaint();
D. drawing();
33. Select valid identifier of Java:
A. userName
B. %passwd
C. 3d_game
D. $charge E. this
34. Which are Java keyword?
A. goto
B. null
C. FALSE
D. native
E. const
35. Run a corrected class: java ?Ccs AClass a b c
Which statement is true?
A. args[0]=”-cs”;
B. args[1]=”a b c”;
C. args[0]=”java”;
D. args[0]=”a”; E. args[1]=?b?
36. Give the following java class:
public class Example{
static int x[]=new int[15];
public static void main(String args[]){
System.out.println(x[5]);
}
}
Which statement is corrected?
A. When compile, some error will occur.
B. When run, some error will occur.
C. Output is zero.
D. Output is null.
37. Give the following java class:
public class Example{
public static void main(String args[]){
static int x[] = new int[15];
System.out.println(x[5]);
}
}
Which statement is corrected?
A. When compile, some error will occur.
B. When run, some error will occur.
C. Output is zero.
D. Output is null.
38. Short answer:
The decimal value of i is 12, the octal i value is:
39. Short answer:
The decimal value of i is 7, the hexadecimal i value is:
40. Which is the range of char?
A. 27~27-1
B. 0~216-1
C. 0~216
D. 0~28 41. Which is the range of int type?
A. -216~216-1
B.- 231~231-1
C. -232~232-1
D. -264~264-1
42. Give the following class:
public class Example{
String str=new String(“good”);
char ch[]={
public static void main(String args[]){
Example ex=new Example();
ex.change(ex.str,ex.ch);
System.out.println(ex.str ”and” ex.ch);
}
public void change(String str,char ch[]){
str=”test ok”;ch[0]=?g?
}
}
Which is the output:
A. good and abc
B. good and gbc
C. test ok and abc
D. test ok and gbc
43. Which code fragments would correctly identify the number of arguments passed via command line to a Java application, exclude the name of the class that is being invoke.
A. int count = args.length;
B. int count = args.length-1;
C. int count=0; while(args[count]!=null)
count ;
D. int count=0;while
(!(args[count].equals(“”))) count ;
44. FilterOutputStream is the parent class for BufferedOutputStream, DataOutputStream and PrintStream. Which classes are valid argument for the constructor of a FilterOutputStream?
A. InputStream
B. OutputStream
C. File
D. RandomAccessFile
E. StreamTokenizer
45. Given a TextArea using a proportional pitch font and constructed like this:
TextArea t=new TextArea(“12345”,5,5);
Which statement is true?
A. The displayed width shows exactly five characters one each line unless otherwise constrained
B. The displayed height is five lines unless otherwise constrained
C. The maximum number of characters in a line will be five
D. The user will be able to edit the character string
E. The displayed string can use multiple fonts
46. Given a List using a proportional pitch font and constructed like this:
List l=new List(5,true);
Which statement is true?
A. The displayed item exactly five lines unless otherwise constrained
B. The displayed item is five lines init, but can displayed more than five Item by scroll
C. The maximum number of item in a list will be five.
D. The list is multiple mode
47. Given this skeleton of a class currently under construction:
public class Example{
int x,y,z;
public Example (int a, int b) {
//lots of complex computation
x=a; y=b;
}
public Example(int a, int b, int c){
// do everything the same as single argument
// version of constructor
// including assignment x=a, y=b, z=c
z=c;
}
}
What is the most concise way to code the “do everything…” part of the constructor taking two arguments?
Short answer:
48. Which correctly create a two dimensional array of integers?
A. int a[][] = new int[][];
B. int a[10][10] = new int[][];
C. int a[][] = new int[10][10];
D. int [][]a = new int[10][10];
E. int []a[] = new int[10][10];
49. Which are correct class declarations? Assume in each case that the text constitutes the entire contents of a file called Fred.java?
A. public class Fred{
public int x = 0;
public Fred (int x){
this.x=x;
}
}
B. public class fred{
public int x = 0;
public Fred (int x){
this.x=x;
}
}
C. public class Fred extends MyBaseClass, MyOtherBaseClass{
public int x = 0;
public Fred(int xval){
x=xval;
}
}
D. protected class Fred{
private int x = 0;
private Fred (int xval){
x=xval;
}
}
E. import java.awt.*;
public class Fred extends Object{
int x;
private Fred(int xval){
x = xval;
}
} 50. A class design requires that a particular member variable must be accessible for direct access by any subclasses of this class. but otherwise not by classes which are not members of the same package. What should be done to achieve this?
A. The variable should be marked public
B. The variable should be marked private
C. The variable should be marked protected
D. The variable should have no special access modifier
E. The variable should be marked private and an accessor method provided
答案及詳細分析：
26。A、C、E
考察的知識點是比較基本類型與對象類型的不同之處，基本類型進行的是值比較，而對象類型進行的是地址比較，也就是對指向它們內存地址的指針進行比較。
27。E
在程序中實現字節與字符轉換時，采用規范“ISO8859-1”是最適宜的方式。
28。B、D、E
移位操作只對整型有效，故不能選A;String類型并非數組，故不能用C所示方法取其中的某一位;B中的length方法返回字符串長度;D中trim方法返回字符串去掉其前后的空格后的新字符串;字符串可以用“ ”進行合并。
29。E
回答本題時要細心閱讀程序，注意“void Mistery(){}”并非構造函數，因為構造函數是沒有返回值時，它只是與類名一致的方法名而已。注意到這一點，此題就沒有什么難度了。
30。C、D
考察對布局管理器知識的掌握情況。BorderLayout的特性是當容器的尺寸改變時，North、South、West、East位置控件的較窄邊長度不變，較長邊長度變化。但控件的相對位置不變。
31。A
FlowLayout的特性是其中的控件大小不隨著容器尺寸的變化而變化，但控件的相對位置會有所改變。
32。A(多選)
請注意，此題雖然是多選題，但正確答案只有一個。不管在什么情況下，圖形要進行重繪，最終總會調用paint()方法，而且也只有paint()方法總會被調用。
33。A、D
Java中的標識符是以字符開頭，字符包括字母、下劃線“_”、美圓符“$”。不能以數字開頭，也不能是Java關鍵字。
34。A、B、D、E
注意：goto、const是Java關鍵字，但是不使用。
35。D
cs是運行時可選擇的java命令的參數，類名后才是由用戶指定的傳入程序中的實參，并且參數是字符串類型，故E也是不正確的。
36。C
數組是引用類型，它的元素相當于類的成員變量，而成員變量是可以被隱式初始化的，所以數組的元素也可以被隱式初始化，int類型被隱式初始化為0，所以選擇C。
37。A
自動變量不能被static修飾，如果將static關鍵字去掉，答案選擇C。
38。014
將十進制化成八進制后在數字前加“0”。
39。0x7
十六進制數用在數字前加“0x”表示。
40。B
字符類型是用16位UniCode表示的。
41。B
整型數的取值范圍是- 2n~2n-1，n表示各種類型的表示位數。
42。B
JAVA中的參數傳遞全是值傳遞，所不同的是，對于引用類型來說，變量內部存放的是對象內存空間的引用，所以引用類型在進行參數傳遞時，是將引用拷貝給形式參數。所以在方法中絕不可能改變主調方法中引用變量的引用，但是可能改變主調方法中引用變量的某一屬性(就象對ch[0]的改變一樣)。
43。A
注意main()方法的參數數組是在程序運行時由系統創建的，大小已經固定了。選項C、D引用args[count]可能會導致數組指針越界異常。
44。B
請查閱類結構，并注意他們的繼承關系。這主要考查流鏈知識點。
45。B
控件TextArea如題中的構造方法的后兩個參數分別表示行、列。注意題中的關鍵詞語“prorortional pitch”，所以不一定是5列字，但一定是5行。
46。B
“5”表示可以選擇的項目數顯示為5行，但可以拖動滑塊觀察其它選項。“true”表示可以多選。
47。this(a,b);
注意教材中提到使用this方法可以簡化構造函數的編寫。此時它必須放在構造函數的第一句。
48。C、D、E
JAVA語言中聲明數組時，方括號與變量的位置關系非常靈活。
49。A、E
Java中大小寫敏感，注意文件名是Fred.java，故B錯誤;Java中不支持多繼承，故C錯誤;Java中與文件名相同的類名的訪問權限一定是public，故D錯誤。
50。C
請查閱關于訪問權限的表格說明。
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