Prepare SCJP 310-035

Author: Razvan MIHAIU
razvan_rem@rem_mihaiu.name (please remove '_rem' and 'rem_')
From: www.mihaiu.name
Date: 17/10/2004

Page 1: SCJP questions 1-20

Page 2: SCJP questions 21-40





  1. What is the output of the following code ?

    Long longL1 = new Long(5); int intI1 = 5; if (longL1.equals(intI1)) System.out.println("longL1 is equal with intI1");

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile: all equals() methods are taking Object references as parameter.

  2. What is the output of the following code ?
    public void someMethod() { int arr[]; arr[0] = 23; System.out.println(arr[0]); }

    \/\/\/\/\/\/\/\/\/\/

    The code does NOT compile ! The array must be initialized after declaration:

    int arr[] = new int [10];
  3. What is the output of the following code ?
    public static void printResult(Integer arr[]) { if (arr instanceof Float[]) System.out.println("arr is instance of Float[]"); }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! Since the reference 'arr' can never point to an instance type Float[] the compiler flags this as an error. OTOH a reference of type Object can point to an object of type Float[]:

    public static void printResult(Object obj) { if (obj instanceof Float[]) System.out.println("obj is instance of Float[]"); }
  4. What is wrong with the following code ?
    int []fontSize = {9, 11, 17, 21}; String [][] fintDesc = { {"TimesNewRoman", "bold"}, {"Courier", "italic"}, {"DingBats", "normal"}};

    \/\/\/\/\/\/\/\/\/\/

    Nothing ! An array can be directly initialized this way.

  5. Does the following code compile ?
    char c = 4096;

    \/\/\/\/\/\/\/\/\/\/

    Yes ! 4096 fits in a char (the compiler is smart enough to see that the integer 4096 will fit in a char; an automatic conversion from int to char is performed)

  6. What is the output of the following code ?

    char ch = 'c'; switch(ch) { case 1: System.out.println("1");break; case -1: System.out.println("-1");break; default: System.out.println("default");break; }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! (the constant -1 is out of the range of char)

  7. What is the output of the following code ?
    long ll = 100; switch(ll) { case 1: System.out.println("1");break; case -1: System.out.println("-1");break; default: System.out.println("default");break; }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! Only integers or types that can be promoted to an integer ("byte", "char" and "short") can appear in a switch statement.

  8. What is the output of the following code ?
    Integer ii = new Integer(23); switch(ii) { case 1: System.out.println("1");break; case -1: System.out.println("-1");break; default: System.out.println("default");break; }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! The Integer class cannot be used instead of primary type int.

  9. In Java there are 4 types of datatypes: primitives, classes, interfaces and arrays. True/False

    \/\/\/\/\/\/\/\/\/\/

    Answer: True.

  10. Java provides 4 primitive data types: characters, integers, floating and boolean.

    \/\/\/\/\/\/\/\/\/\/

    Answer: Yes.

  11. How many bits are used to store a boolean value ?

    \/\/\/\/\/\/\/\/\/\/

    The number of bits is system-dependent. Java guarantees that a boolean can store true or false values but it does not specify how many bits will be used to actually store that info.

  12. Can you compile and run the following code ?
    public class SimpleJava { static void main(String args[]) { System.out.println("SimpleJava ...."); } }

    \/\/\/\/\/\/\/\/\/\/

    You can compile but you cannot run. (the main method is not public)

  13. Which statement is true about the following code?
    public class CDummy { public static void main(String argv[]) { String str1 = new String("test1"); StringBuffer str2 = new StringBuffer("test2"); printIt(str1); printIt(str2); } public static void printIt(String s) { System.out.println(s); } }

    \/\/\/\/\/\/\/\/\/\/

    This code will not compile. An instance of StringBuffer cannot be passed to a method that is expecting an instance of String.

  14. What is the output of the following code ?
    public class CDummy { public static void main(String args[]) { System.out.println("CDummy..."); try { doIt(); } catch (RuntimeException ee) {;} catch (ArithmeticException ee) {;} catch (Exception ee) {;} } static void doIt() throws ArithmeticException, RuntimeException, Exception { System.out.println("DoIt!"); } }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! The catch exception order is wrong. The exception order should be:

    catch (ArithmeticException ee) {;} catch (RuntimeException ee) {;} catch (Exception ee) {;}
  15. What is the output of the following code ?
    public class CDummy { public static void main(String args[]) { System.out.println("CDummy..."); doIt(); } static public doIt() { System.out.println("DoIt!"); } }

    \/\/\/\/\/\/\/\/\/\/

    The code does not compile ! The function doIt() must have a return type.

  16. If the System.exit() function is called in a catch block, will the finally block be executed ?

    \/\/\/\/\/\/\/\/\/\/

    No ! The current thread will instantly finish.

  17. If the return() function is called in a catch block, will the finally block be executed ?

    \/\/\/\/\/\/\/\/\/\/

    Yes !

  18. Will the following code compile ?
    static int doIt() throws ArithmeticException, RuntimeException, Exception { System.out.println("DoIt!"); throw new ArithmeticException(); return 7; }

    \/\/\/\/\/\/\/\/\/\/

    No ! The return statement is unreachable.

  19. What is the output of the following program ?
    public class CDummy { public static void main(String args[]) { System.out.println("CDummy..."); System.out.println("textX() = " + testX()); } public static int testX() { try { return 1; }catch(ArithmeticException aex) { return 2 ; }catch(Exception ex) { return 3; }finally { return 4; } } }

    \/\/\/\/\/\/\/\/\/\/

    The output is 4. Because the finally clause is calling return there is a warning, because the return code 1 (from the try block) is discarded.

  20. What is the output of the following program ?
    public class CDummy { public static void main(String args[]) { System.out.println("CDummy..."); System.out.println("textX() = " + testX()); } public static int testX() { try { throw new ArithmeticException(); }catch(ArithmeticException aex) { return 2 ; }catch(Exception ex) { return 3; }finally { return 4; } } }

    \/\/\/\/\/\/\/\/\/\/

    The output is 4. Because the finally clause is calling return there is a warning, because the return code 2 (from the catch block) is discarded.










Best regards,
Razvan MIHAIU



Razvan Mihaiu � 2000 - 2017