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- Question
Which of the following are legal lines of code?
- int w = (int)888.8;
- byte x = (byte)1000L;
- long y = (byte)100;
- byte z = (byte)100L;
Options- A. 1 and 2
- B. 2 and 3
- C. 3 and 4
- D. All statements are correct.
- Correct Answer
- All statements are correct.
ExplanationStatements (1), (2), (3), and (4) are correct. (1) is correct because when a floating-point number (a double in this case) is cast to an int, it simply loses the digits after the decimal.(2) and (4) are correct because a long can be cast into a byte. If the long is over 127, it loses its most significant (leftmost) bits.
(3) actually works, even though a cast is not necessary, because a long can store a byte.
Operators and Assignments problems
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- 1. Which two are equal?
- 32/4
- (8 >> 2) << 4
- 2^5
- 128 >>> 2
- 2 >> 5
Options- A. 1 and 2
- B. 2 and 4
- C. 1 and 3
- D. 2 and 3 Discuss
Correct Answer: 2 and 4
Explanation:
(2) and (4) are correct. (2) and (4) both evaluate to 32. (2) is shifting bits right then left using the signed bit shifters >> and <<. (4) is shifting bits using the unsigned operator >>>, but since the beginning number is positive the sign is maintained.(1) evaluates to 8, (3) looks like 2 to the 5th power, but ^ is the Exclusive OR operator so (3) evaluates to 7. (5) evaluates to 0 (2 >> 5 is not 2 to the 5th).
- 2. Which two statements are equivalent?
- 16*4
- 16>>2
- 16/2^2
- 16>>>2
Options- A. 1 and 2
- B. 2 and 4
- C. 3 and 4
- D. 1 and 3 Discuss
Correct Answer: 2 and 4
Explanation:
(2) is correct. 16 >> 2 = 4(4) is correct. 16 >>> 2 = 4
(1) is wrong. 16 * 4 = 64
(3) is wrong. 16/2 ^ 2 = 10
- 3. Which two of the following statements, inserted independently, could legally be inserted into missing section of this code?
- boolean test = (Component instanceof t);
- boolean test = (t instanceof Ticker);
- boolean test = t.instanceof(Ticker);
- boolean test = (t instanceof Component);
import java.awt.*; class Ticker extends Component { public static void main (String [] args) { Ticker t = new Ticker(); /* Missing Statements? */ } }
Options- A. 1 and 4
- B. 2 and 3
- C. 1 and 3
- D. 2 and 4 Discuss
Correct Answer: 2 and 4
Explanation:
(2) is correct because class type Ticker is part of the class hierarchy of t; therefore it is a legal use of the instanceof operator. (4) is also correct because Component is part of the hierarchy of t, because Ticker extends Component.(1) is incorrect because the syntax is wrong. A variable (or null) always appears before the instanceof operator, and a type appears after it. (3) is incorrect because the statement is used as a method (t.instanceof(Ticker);), which is illegal.
- 4. Which three statements are true?
- f1 == f2
- f1 == f3
- f2 == f1[1]
- x == f1[0]
- f == f1[0]
import java.awt.Button; class CompareReference { public static void main(String [] args) { float f = 42.0f; float [] f1 = new float[2]; float [] f2 = new float[2]; float [] f3 = f1; long x = 42; f1[0] = 42.0f; } }
Options- A. 1, 2 and 3
- B. 2, 4 and 5
- C. 3, 4 and 5
- D. 1, 4 and 5 Discuss
Correct Answer: 2, 4 and 5
Explanation:
(2) is correct because the reference variables f1 and f3 refer to the same array object.(4) is correct because it is legal to compare integer and floating-point types.
(5) is correct because it is legal to compare a variable with an array element.
(3) is incorrect because f2 is an array object and f1[1] is an array element.
- 5. In the given program, how many lines of output will be produced?
public class Test { public static void main(String [] args) { int [] [] [] x = new int [3] [] []; int i, j; x[0] = new int[4][]; x[1] = new int[2][]; x[2] = new int[5][]; for (i = 0; i < x.length; i++) { for (j = 0; j < x[i].length; j++) { x[i][j] = new int [i + j + 1]; System.out.println("size = " + x[i][j].length); } } } }
Options- A. 7
- B. 9
- C. 11
- D. 13
- E. Compilation fails Discuss
Correct Answer: 11
Explanation:
The loops use the array sizes (length).It produces 11 lines of output as given below.
D:\Java>javac Test.java D:\Java>java Test size = 1 size = 2 size = 3 size = 4 size = 2 size = 3 size = 3 size = 4 size = 5 size = 6 size = 7
Therefore, 11 is the answer.
- 6. Which two statements are equivalent?
- 3/2
- 3<2
- 3*4
- 3<<2
Options- A. 1 and 2
- B. 2 and 3
- C. 3 and 4
- D. 1 and 4 Discuss
Correct Answer: 3 and 4
Explanation:
(1) is wrong. 3/2 = 1 (integer arithmetic).(2) is wrong. 3 < 2 = false.
(3) is correct. 3 * 4 = 12.
(4) is correct. 3 <<2= 12. In binary 3 is 11, now shift the bits two places to the left and we get 1100 which is 12 in binary (3*2*2).
- 7. Given that EOFException and FileNotFoundException are both subclasses of IOException, and further assuming this block of code is placed into a class, which statement is most true concerning this code?
System.out.print("Start "); try { System.out.print("Hello world"); throw new FileNotFoundException(); } System.out.print(" Catch Here "); /* Line 7 */ catch(EOFException e) { System.out.print("End of file exception"); } catch(FileNotFoundException e) { System.out.print("File not found"); }
Options- A. The code will not compile.
- B. Code output: Start Hello world File Not Found.
- C. Code output: Start Hello world End of file exception.
- D. Code output: Start Hello world Catch Here File not found. Discuss
Correct Answer: The code will not compile.
Explanation:
Line 7 will cause a compiler error. The only legal statements after try blocks are either catch or finally statements.Option B, C, and D are incorrect based on the program logic described above. If line 7 was removed, the code would compile and the correct answer would be Option B.
- 8. Given that all methods of class FileOutputStream, including close(), throw an IOException, which of these is true?
import java.io.*; public class MyProgram { public static void main(String args[]) { FileOutputStream out = null; try { out = new FileOutputStream("test.txt"); out.write(122); } catch(IOException io) { System.out.println("IO Error."); } finally { out.close(); } } }
Options- A. This program will compile successfully.
- B. This program fails to compile due to an error at line 4.
- C. This program fails to compile due to an error at line 6.
- D. This program fails to compile due to an error at line 18. Discuss
Correct Answer: This program fails to compile due to an error at line 18.
Explanation:
Any method (in this case, the main() method) that throws a checked exception (in this case, out.close() ) must be called within a try clause, or the method must declare that it throws the exception. Either main() must declare that it throws an exception, or the call to out.close() in the finally block must fall inside a (in this case nested) try-catch block.- 9. Which statement is true?
Options- A. A try statement must have at least one corresponding catch block.
- B. Multiple catch statements can catch the same class of exception more than once.
- C. An Error that might be thrown in a method must be declared as thrown by that method, or be handled within that method.
- D. Except in case of VM shutdown, if a try block starts to execute, a corresponding finally block will always start to execute. Discuss
- An exception arising in the finally block itself.
- The death of the thread.
- The use of System.exit()
- Turning off the power to the CPU.
Correct Answer: Except in case of VM shutdown, if a try block starts to execute, a corresponding finally block will always start to execute.
Explanation:
A is wrong. A try statement can exist without catch, but it must have a finally statement.B is wrong. A try statement executes a block. If a value is thrown and the try statement has one or more catch clauses that can catch it, then control will be transferred to the first such catch clause. If that catch block completes normally, then the try statement completes normally.
C is wrong. Exceptions of type Error and RuntimeException do not have to be caught, only checked exceptions (java.lang.Exception) have to be caught. However, speaking of Exceptions, Exceptions do not have to be handled in the same method as the throw statement. They can be passed to another method.
If you put a finally block after a try and its associated catch blocks, then once execution enters the try block, the code in that finally block will definitely be executed except in the following circumstances:
- 10. Which statement is true?
Options- A. catch(X x) can catch subclasses of X where X is a subclass of Exception.
- B. The Error class is a RuntimeException.
- C. Any statement that can throw an Error must be enclosed in a try block.
- D. Any statement that can throw an Exception must be enclosed in a try block. Discuss
Correct Answer: catch(X x) can catch subclasses of X where X is a subclass of Exception.
Explanation:
Option A is correct. If the class specified in the catch clause does have subclasses, any exception object that subclasses the specified class will be caught as well.Option B is wrong. The error class is a subclass of Throwable and not Runtime Exception.
Option C is wrong. You do not catch this class of error.
Option D is wrong. An exception can be thrown to the next method higher up the call stack.
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- 1. Which two are equal?