java经典常用笔试题（一）

1.
 1)  public class ReturnIt{
   
   
 2)  returnType methodA(byte x, double y){
   
   
 3)  return (short)x/y*2;
 4)  }
 5)  }
 what is valid returnType for methodA in line 2?
Answer:double

2.
 1)  class Super{
   
   
 2)  public float getNum(){
   
   return 3.0f;}
 3)  }
 4)
 5)  public class Sub extends Super{
   
   
 6)
 7)  }
which method, placed at line 6, will cause a compiler error?
A. public float getNum(){
   
   return 4.0f;}
B. public void getNum(){
   
   }
C. public void getNum(double d){
   
   }
D. public double getNum(float d){
   
   return 4.0d;}
Answer:B

3. public class IfTest{
   
   
 public static void main(String args[]){
   
   
        int x=3;
 int y=1;
 if(x=y)
 System.out.println("Not equal");
 else
 System.out.println("Equal");
 }
 }
 what is the result?
Answer:compile error

4. public class Foo{
   
   
  public static void main(String args[]){
   
   
  try{
   
   return;}
   finally{
   
    System.out.println("Finally");}
   }
    }
 what is the result?
 A. print out nothing
 B. print out "Finally"
 C. compile error
Answer:B

5. public class Test{
   
   
  public static String output="";
   public static void foo(int i){
   
   
    try {
   
   
if(i==1){
   
   
throw new Exception();
}
output +="1";
 }
 catch(Exception e){
   
   
 output+="2";
 return;
 }
 finally{
   
   
 output+="3";
  }
 output+="4";
 }
 public static void main(String args[]){
   
   
 foo(0);
 foo(1);
 24)  
    }
    }
 what is the value of output at line 24?

Answer:13423

6. public class IfElse{
   
   
 public static void main(String args[]){
   
   
 if(odd(5))
 System.out.println("odd");
 else
 System.out.println("even");
 }
  public static int odd(int x){
   
   return x%2;}  
  }
  what is output?


Answer:Compile Error

7. class ExceptionTest{
   
   
  public static void main(String args[]){
   
   
  try{
   
   
methodA();
}
  catch(IOException e){
   
   
System.out.println("caught IOException");
  }
  catch(Exception e){
   
   
  System.out.println("caught Exception");
   }
  }
  }
 If methodA() throws a IOException, what is the result?
Answer:caught IOException
exception can catch once only
if change the sequence of catch
  catch(IOException e) can't execute  and compiler will report rongyu error

8. int i=1,j=10;
 do{
   
   
 if(i++>--j) continue;
 }while(i<5);
After Execution, what are the value for i and j?
A. i=6 j=5
B. B.i=5 j=5
C. i=6 j=4
D. i=5 j=6
E. i=6 j=6
Answer:D

9. 1)public class X{
   
   
 2) public Object m(){
   
   
 3) Object o=new Float(3.14F);
 4) Object[] oa=new Object[1];
 5) oa[0]=o;
 6) o=null;
 7) oa[0]=null;
 System.out.println(oa[0]);
 9) }
 10) }
 which line is the earliest point the object a refered is definitely elibile
 to be garbage collectioned?
 A.After line 4   B. After line 5  C.After line 6  
 D.After line 7   E.After line 9(that is,as the method returns)
Answer:D

10.    1)  interface Foo{
   
   
     2)int k=0;
     3) }
     4) public class Test implements Foo{
   
   
     5) public static void main(String args[]){
   
   
     6)int i;
     7)Test test =new Test();
     8)i=test.k;
     9)i=Test.k;
    10)i=Foo.k;
    11)     }
    12) }
   what is the result?
Answer:compile successed and i=0

11. what is reserved words in java?
  A. run
  B. default
  C. implement
  D. import
Answer:B,D

12. public class Test{
   
   
   public static void main(String[] args){
   
   
   String foo=args[1];
   Sring bar=args[2];
   String baz=args[3];
    }
    }
   java Test Red Green Blue
  what is the value of baz?
  A. baz has value of ""
  B. baz has value of null
  C. baz has value of "Red"
  D. baz has value of "Blue"
  E. baz has value of "Green"
  F. the code does not compile
  G. the program throw an exception
Answer:G

13. int index=1;
  int foo[]=new int[3];
  int bar=foo[index];
  int baz=bar+index;
  what is the result?
  A. baz has a value of 0
  B. baz has value of 1
  C. baz has value of 2
  D. an exception is thrown
  E. the code will not compile
Answer:B

14. which three are valid declaraction of a float?
   A. float foo=-1;
   B. float foo=1.0;
   C. float foo=42e1;
   D. float foo=2.02f;
   E. float foo=3.03d;
   F. float foo=0x0123;
Answer:A,D,F

15. public class Foo{
   
   
   public static void main(String args[]){
   
   
   String s;
   System.out.println("s="+s);
    }
   }
   what is the result?
Answer:compile error

16.   1) public class Test{
   
   
    2) public static void main(String args[]){
   
   
    3) int i=oxFFFFFFF1;
    4) int j=~i;
    5)
    6) }
    7) }
  which is decimal value of j at line 5?
  A. 0      B.1    C.14    D.-15    E. compile error at line 3    
  F. compile error at line 4
Answer:C

17. float f=4.2F;
  Float g=new Float(4.2F);
  Double d=new Double(4.2);
  Which are true?
  A. f==g   B. g==g   C. d==f   D. d.equals(f)  E d.equals(g)  F. g.equals(4.2);
Answer:B,E

18.  public class Test{
   
   
   public static void add3(Integer i){
   
   
 3) int val=i.intvalue();
    val+=3;
    i=new Integer(val);
    }
    public static void main(String args[]){
   
   
     Integer i=new Integer(0);
        add3(i);
     System.out.println(i.intvalue());
     }
       }
    what is the  result?
    A. compile fail       B.print out "0"      C.print out "3"  
    D.compile succeded but exception at line 3
Answer:B

19. public class Test{
    public static void main(String[] args){
    System.out.println(6^3);
    }
    }
    what is output?
    Answer:5
    ^ is yi huo

20. public class Test{
   
   
   public static void stringReplace(String text){
   
   
     text=text.replace('j','l');
    }
    public static void bufferReplace(StringBuffer text){
   
   
      text=text.append("c");
     }
   public static void main(String args[]){
   
     
     String textString=new String("java");
     StringBuffer textBuffer=new StringBuffer("java");
      StringReplace(textString);
      bufferReplace(textBuffer);
    System.out.println(textString+textBuffer);
      }
      }
   what is the output?
Answer:javajavac

21. public class ConstOver{
   
   
   public ConstOver(int x, int y, int z){
   
   }
    }
   which two overload the ConstOver constructor?
   A.ConstOver(){
   
   }
   B.protected int ConstOver(){
   
   }   //not overload ,but no a error
   C.private ConstOver(int z, int y, byte x){
   
   }
   D.public void ConstOver(byte x, byte y, byte z){
   
   }
   E.public Object ConstOver(int x, int y, int z){
   
   }
Answer:A,C

22. public class MethodOver{
   
   
    public void setVar(int a, int b, float c){
   
   }
    }
   which overload the setVar?
   A.private void setVar(int a, float c, int b){
   
   }
   B.protected void setVar(int a, int b, float c){
   
   }
   C.public int setVar(int a, float