简答题：

指出下面代码的错误，说明原因。
interface  a{
   int x = 0;
}
class b{
   int x =1;
}
class c extends b implements a {
   public void px(){
      system.out.println(x);
   }
   public static void main(string[] args) {
      new c().px();
   }
}

写出输出结果：
public class test
{
   public static int a = 5;

   public static void main(string[] args)
  {
     test test = new test();

     test = null;

     system.out.println(test.a);
  }

} 

class something {
    final int i;
    public void dosomething() {
        system.out.println("i = " + i);
    }
}
上面代码正确还是错误？为什么。

介绍java中的collection framework(包括如何写自己的数据结构)?

class something {
    int i;
    public void dosomething() {
        system.out.println("i = " + i);
    }
}
代码是否有错？为什么。

找出以下程序错误。
class test{
    private string par1;
    private string par2;
    test(){
    }
    
    public static void main(string[] arg){
        int a ;
        if(a){
            system.out.println("par1="+par1);
        }else{
            system.out.println("par2=" + par2);
        }
    }
}

选择题：

what will happen when you attempt to compile and run the following code?

(assume that the code is compiled and run with assertions enabled.)

public class asserttest{

public void methoda(int i){

assert i >= 0 : methodb();

system.out.println(i);

}

public void methodb(){  

system.out.println("the value must not be negative");

}

public static void main(string args[]){

asserttest test = new asserttest();

test.methoda(-10); 

}

}

what will happen when you attempt to compile and run the following code? 

class base 

{

int i = 99; 

public void amethod()

{

       system.out.println("base.amethod()");

     }

     base()

{

     amethod();

     }

} 

public class derived extends base

{

int i = -1;

       

public static void main(string argv[])

{

     base b = new derived();

       system.out.println(b.i);

       b.amethod();

     } 

     public void amethod()

{

       system.out.println("derived.amethod()");

     } 

} 

choices:

what will be printed when you execute the following code? 

class x 
{
  y b = new y();
  x() 
 { 
   system.out.print("x"); 
  }
} 

class y 
{
    y() 
   { 
     system.out.print("y"); 
   }
} 

public class z extends x 
{
   y y = new y(); 
  z() 
 { 
    system.out.print("z"); 
  } 
   public static void main(string[] args) 
  {
               new z();
  }
} 

choices:

which is the most appropriate code snippet that can be inserted at line 18 in the following code?

(assume that the code is compiled and run with assertions enabled)

1.  import java.util.*;

2. 

3.  public class asserttest

4.  {

5.      private hashmap cctld;

6.     

7.      public asserttest()

8.      {

9.          cctld = new hashmap();

10.         cctld.put("in", "india");

11.         cctld.put("uk", "united kingdom");

12.         cctld.put("au", "australia");

13.         // more code... 

14.     }

15.     // other methods ....  

16.     public string getcountry(string countrycode)

17.     {

18.         // what should be inserted here?

19.         string country = (string)cctld.get(countrycode);

20.         return country;

21.     }

22. }

give the following method:
 public void method( ){
 string a,b;
 a=new string(“hello world”);
 b=new string(“game over”);
 system.out.println(a+b+”ok”);
 a=null;
 a=b;
 system.out.println(a);
 } 
in the absence of compiler optimization, which is the earliest point the object a refered is definitely elibile to be garbage collection.

     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;
     8.return o;
     9. }
     10.} 
     when is the float object created in line 3, eligible for garbage collection? 

given 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 valid answer: 

what will be the result of executing the following code? 

// filename; superclassx.java

package packagex; 

public class superclassx

{

protected void superclassmethodx()

{

}

int superclassvarx;

} 

 

// filename subclassy.java

1.package packagex.packagey;

2.

3.public class subclassy extends superclassx

4.{

5.superclassx objx = new subclassy();

6.subclassy objy = new subclassy();

7.void subclassmethody()

8.{

9.objy.superclassmethodx();

10.int i;

11.i = objy.superclassvarx;

12.}

13.} 

choices:

what is the result when you compile and run the following code? 

public class test

{ 

public void method()

{

for(int i = 0; i < 3; i++)

       {

       system.out.print(i);

       }

       system.out.print(i);

}

} 

choices:

what results from attempting to compile and run the following code? 

public class ternary

{

public static void main(string args[])

{

int a = 5;

system.out.println("value is - " + ((a < 5) ? 9.9 : 9));

}

} 

choices:

string s=”example string”;which operation is not legal?

given 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 valid answer: 

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?

select valid identifier of java:

which is the most appropriate code snippet that can be inserted at line 18 in the following code?

(assume that the code is compiled and run with assertions enabled)

1.  import java.util.*;

2. 

3.  public class asserttest

4.  {

5.      private hashmap cctld;

6.     

7.      public asserttest()

8.      {

9.          cctld = new hashmap();

10.         cctld.put("in", "india");

11.         cctld.put("uk", "united kingdom");

12.         cctld.put("au", "australia");

13.         // more code... 

14.     }

15.     // other methods ....  

16.     public string getcountry(string countrycode)

17.     {

18.         // what should be inserted here?

19.         string country = (string)cctld.get(countrycode);

20.         return country;

21.     }

22. }

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);
}
}

what will be printed when you execute the following code? 

class x 
{
  y b = new y();
  x() 
 { 
   system.out.print("x"); 
  }
} 

class y 
{
    y() 
   { 
     system.out.print("y"); 
   }
} 

public class z extends x 
{
   y y = new y(); 
  z() 
 { 
    system.out.print("z"); 
  } 
   public static void main(string[] args) 
  {
               new z();
  }
} 

choices:

what will happen when you attempt to compile and run the following code?

(assume that the code is compiled and run with assertions enabled.)

public class asserttest{

public void methoda(int i){

assert i >= 0 : methodb();

system.out.println(i);

}

public void methodb(){  

system.out.println("the value must not be negative");

}

public static void main(string args[]){

asserttest test = new asserttest();

test.methoda(-10); 

}

}

which is the most appropriate code snippet that can be inserted at line 18 in the following code?

(assume that the code is compiled and run with assertions enabled)

1.  import java.util.*;

2. 

3.  public class asserttest

4.  {

5.      private hashmap cctld;

6.     

7.      public asserttest()

8.      {

9.          cctld = new hashmap();

10.         cctld.put("in", "india");

11.         cctld.put("uk", "united kingdom");

12.         cctld.put("au", "australia");

13.         // more code... 

14.     }

15.     // other methods ....  

16.     public string getcountry(string countrycode)

17.     {

18.         // what should be inserted here?

19.         string country = (string)cctld.get(countrycode);

20.         return country;

21.     }

22. }

string s=”example string”;which operation is not legal?

下述程序代码中有语法错误的行是（  ）。
int i,ia[10],ib[10];      /*第一行*/
for (i=0;i<=9;i++)        /*第2行*/
  ia[i]=0;          /*第3行*/
ib=ia;    /*第4行*/

what will happen when you attempt to compile and run the following code? 

class base 

{

int i = 99; 

public void amethod()

{

       system.out.println("base.amethod()");

     }

     base()

{

     amethod();

     }

} 

public class derived extends base

{

int i = -1;

       

public static void main(string argv[])

{

     base b = new derived();

       system.out.println(b.i);

       b.amethod();

     } 

     public void amethod()

{

       system.out.println("derived.amethod()");

     } 

} 

choices:

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?

public class x{

   public object m(){

      object o = new float(3.14f);//line 3

      object [] oa = new object[1];//line 4

      oa[0] = o;//line 5

      o=null;//line 6

      return oa[0];//line 7

     }

}
when is the float object, created in line 3,eligible for garbage collection?

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?

what will be the result of executing the following code? 

// filename; superclassx.java

package packagex; 

public class superclassx

{

protected void superclassmethodx()

{

}

int superclassvarx;

} 

 

// filename subclassy.java

1.package packagex.packagey;

2.

3.public class subclassy extends superclassx

4.{

5.superclassx objx = new subclassy();

6.subclassy objy = new subclassy();

7.void subclassmethody()

8.{

9.objy.superclassmethodx();

10.int i;

11.i = objy.superclassvarx;

12.}

13.} 

choices:

what will be printed when you execute the following code? 

class x 
{
  y b = new y();
  x() 
 { 
   system.out.print("x"); 
  }
} 

class y 
{
    y() 
   { 
     system.out.print("y"); 
   }
} 

public class z extends x 
{
   y y = new y(); 
  z() 
 { 
    system.out.print("z"); 
  } 
   public static void main(string[] args) 
  {
               new z();
  }
} 

choices:

what will happen when you attempt to compile and run the following code? 

int output = 10;

boolean b1 = false; 

if((b1 == true) && ((output += 10) == 20))

{

   system.out.println("we are equal " + output);

} 

else

{

   system.out.println("not equal! " + output);

} 

choices:

the following code is entire contents of a file called example.java,causes precisely one error during compilation:
 class subclass extends baseclass{
 }
 class baseclass(){
 string str;
 public baseclass(){
 system.out.println(“ok”);}
 public baseclass(string s){
 str=s;}}
 public class example{
 public void method(){
 subclass s=new subclass(“hello”);
 baseclass b=new baseclass(“world”);
 }
 }

which line would be cause the error? 

下述程序代码中有语法错误的行是（  ）。
int i,ia[10],ib[10];      /*第一行*/
for (i=0;i<=9;i++)        /*第2行*/
  ia[i]=0;          /*第3行*/
ib=ia;    /*第4行*/

what will happen when you attempt to compile and run the following code?

(assume that the code is compiled and run with assertions enabled.)

public class asserttest{

public void methoda(int i){

assert i >= 0 : methodb();

system.out.println(i);

}

public void methodb(){  

system.out.println("the value must not be negative");

}

public static void main(string args[]){

asserttest test = new asserttest();

test.methoda(-10); 

}

}

give the following code:
public class example{
public static void main(string args[] ){
int l=0;
do{
system.out.println(“doing it for l is:”+l);
}while(--l>0)
system.out.println(“finish”);
}
}
which well be output: 

give the following java source fragement:
//point x
public class interesting{
//do something
}
which statement is correctly java syntax at point x? 

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);
}
}

give the code fragment:
if(x>4){
system.out.println(“test 1”);}
else if (x>9){
system.out.println(“test 2”);}
else {
system.out.println(“test 3”);}
which range of value x would produce of output “test 2”? 

what is the result when you compile and run the following code? 

public class test

{ 

public void method()

{

for(int i = 0; i < 3; i++)

       {

       system.out.print(i);

       }

       system.out.print(i);

}

} 

choices:

     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;
     8.return o;
     9. }
     10.} 
     when is the float object created in line 3, eligible for garbage collection?