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- Question
Which three are methods of the Object class?
- notify();
- notifyAll();
- isInterrupted();
- synchronized();
- interrupt();
- wait(long msecs);
- sleep(long msecs);
- yield();
Options- A. 1, 2, 4
- B. 2, 4, 5
- C. 1, 2, 6
- D. 2, 3, 4
- Correct Answer
- 1, 2, 6
Explanation(1), (2), and (6) are correct. They are all related to the list of threads waiting on the specified object.(3), (5), (7), and (8) are incorrect answers. The methods isInterrupted() and interrupt() are instance methods of Thread.
The methods sleep() and yield() are static methods of Thread.
D is incorrect because synchronized is a keyword and the synchronized() construct is part of the Java language.
More questions
- 1. 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. Discuss
Correct Answer: All statements are correct.
Explanation:
Statements (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.
- 2. What will be the output of the program?
int I = 0; label: if (I < 2) { System.out.print("I is " + I); I++; continue label; }
Options- A. I is 0
- B. I is 0 I is 1
- C. Compilation fails.
- D. None of the above Discuss
Correct Answer: Compilation fails.
Explanation:
The code will not compile because a continue statement can only occur in a looping construct. If this syntax were legal, the combination of the continue and the if statements would create a kludgey kind of loop, but the compiler will force you to write cleaner code than this.- 3. What will be the output of the program?
interface Foo141 { int k = 0; /* Line 3 */ } public class Test141 implements Foo141 { public static void main(String args[]) { int i; Test141 test141 = new Test141(); i = test141.k; /* Line 11 */ i = Test141.k; i = Foo141.k; } }
Options- A. Compilation fails.
- B. Compiles and runs ok.
- C. Compiles but throws an Exception at runtime.
- D. Compiles but throws a RuntimeException at runtime. Discuss
Correct Answer: Compiles and runs ok.
Explanation:
The variable k on line 3 is an interface constant, it is implicitly public, static, and final. Static variables can be referenced in two ways:Via a reference to any instance of the class (line 11)
Via the class name (line 12).
- 4. What will be the output of the program?
public class Test { public static void main(String args[]) { int i = 1, j = 0; switch(i) { case 2: j += 6; case 4: j += 1; default: j += 2; case 0: j += 4; } System.out.println("j = " + j); } }
Options- A. j = 0
- B. j = 2
- C. j = 4
- D. j = 6 Discuss
Correct Answer: j = 6
Explanation:
Because there are no break statements, the program gets to the default case and adds 2 to j, then goes to case 0 and adds 4 to the new j. The result is j = 6.- 5. What will be the output of the program?
Float f = new Float("12"); switch (f) { case 12: System.out.println("Twelve"); case 0: System.out.println("Zero"); default: System.out.println("Default"); }
Options- A. Zero
- B. Twelve
- C. Default
- D. Compilation fails Discuss
Correct Answer: Compilation fails
Explanation:
The switch statement can only be supported by integers or variables more "narrow" than an integer i.e. byte, char, short. Here a Float wrapper object is used and so the compilation fails.- 6. What will be the output of the program?
for (int i = 0; i < 4; i += 2) { System.out.print(i + " "); } System.out.println(i); /* Line 5 */
Options- A. 0 2 4
- B. 0 2 4 5
- C. 0 1 2 3 4
- D. Compilation fails. Discuss
Correct Answer: Compilation fails.
Explanation:
Compilation fails on the line 5 - System.out.println(i); as the variable i has only been declared within the for loop. It is not a recognised variable outside the code block of loop.- 7. What will be the output of the program?
import java.util.*; class I { public static void main (String[] args) { Object i = new ArrayList().iterator(); System.out.print((i instanceof List)+","); System.out.print((i instanceof Iterator)+","); System.out.print(i instanceof ListIterator); } }
Options- A. Prints: false, false, false
- B. Prints: false, false, true
- C. Prints: false, true, false
- D. Prints: false, true, true Discuss
Correct Answer: Prints: false, true, false
Explanation:
The iterator() method returns an iterator over the elements in the list in proper sequence, it doesn't return a List or a ListIterator object.A ListIterator can be obtained by invoking the listIterator method.
- 8. What will be the output of the program?
public class CommandArgs { public static void main(String [] args) { String s1 = args[1]; String s2 = args[2]; String s3 = args[3]; String s4 = args[4]; System.out.print(" args[2] = " + s2); } }and the command-line invocation is> java CommandArgs 1 2 3 4
Options- A. args[2] = 2
- B. args[2] = 3
- C. args[2] = null
- D. An exception is thrown at runtime. Discuss
Correct Answer: An exception is thrown at runtime.
Explanation:
An exception is thrown because in the code String s4 = args[4];, the array index (the fifth element) is out of bounds. The exception thrown is the cleverly named ArrayIndexOutOfBoundsException.- 9. 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
- 10. What two statements are true about properly overridden hashCode() and equals() methods?
- hashCode() doesn't have to be overridden if equals() is.
- equals() doesn't have to be overridden if hashCode() is.
- hashCode() can always return the same value, regardless of the object that invoked it.
- equals() can be true even if it's comparing different objects.
Options- A. 1 and 2
- B. 2 and 3
- C. 3 and 4
- D. 1 and 3 Discuss
Correct Answer: 3 and 4
Explanation:
(3) and (4) are correct.(1) and (2) are incorrect because by contract hashCode() and equals() can't be overridden unless both are overridden.
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- 1. Which of the following are legal lines of code?