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- Question
What is the numerical range of a char?
Options- A. -128 to 127
- B. -(215) to (215) - 1
- C. 0 to 32767
- D. 0 to 65535
- Correct Answer
- 0 to 65535
ExplanationA char is really a 16-bit integer behind the scenes, so it supports 2 16 (from 0 to 65535) values. - 1. 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.
- 2. Which statement is true about assertions in the Java programming language?
Options- A. Assertion expressions should not contain side effects.
- B. Assertion expression values can be any primitive type.
- C. Assertions should be used for enforcing preconditions on public methods.
- D. An AssertionError thrown as a result of a failed assertion should always be handled by the enclosing method. Discuss
- 3. What will be the output of the program?
String s = "ABC"; s.toLowerCase(); s += "def"; System.out.println(s);
Options- A. ABC
- B. abc
- C. ABCdef
- D. Compile Error Discuss
- 4. What will be the output of the program?
class Super { public Integer getLength() { return new Integer(4); } } public class Sub extends Super { public Long getLength() { return new Long(5); } public static void main(String[] args) { Super sooper = new Super(); Sub sub = new Sub(); System.out.println( sooper.getLength().toString() + "," + sub.getLength().toString() ); } }
Options- A. 4, 4
- B. 4, 5
- C. 5, 4
- D. Compilation fails. Discuss
- 5. Which statement is true for the class java.util.HashSet?
Options- A. The elements in the collection are ordered.
- B. The collection is guaranteed to be immutable.
- C. The elements in the collection are guaranteed to be unique.
- D. The elements in the collection are accessed using a unique key. Discuss
- 6. What will be the output of the program?
public class Test { private static int[] x; public static void main(String[] args) { System.out.println(x[0]); } }
Options- A. 0
- B. null
- C. Compile Error
- D. NullPointerException at runtime Discuss
- 7. What will be the output of the program?
public class Example { public static void main(String [] args) { double values[] = {-2.3, -1.0, 0.25, 4}; int cnt = 0; for (int x=0; x < values.length; x++) { if (Math.round(values[x] + .5) == Math.ceil(values[x])) { ++cnt; } } System.out.println("same results " + cnt + " time(s)"); } }
Options- A. same results 0 time(s)
- B. same results 2 time(s)
- C. same results 4 time(s)
- D. Compilation fails. Discuss
- 8. What will be the output of the program?
public class ThreadDemo { private int count = 1; public synchronized void doSomething() { for (int i = 0; i < 10; i++) System.out.println(count++); } public static void main(String[] args) { ThreadDemo demo = new ThreadDemo(); Thread a1 = new A(demo); Thread a2 = new A(demo); a1.start(); a2.start(); } } class A extends Thread { ThreadDemo demo; public A(ThreadDemo td) { demo = td; } public void run() { demo.doSomething(); } }
Options- A. It will print the numbers 0 to 19 sequentially
- B. It will print the numbers 1 to 20 sequentially
- C. It will print the numbers 1 to 20, but the order cannot be determined
- D. The code will not compile. Discuss
- 9. Which statement is true?
Options- A. If only one thread is blocked in the wait method of an object, and another thread executes the modify on that same object, then the first thread immediately resumes execution.
- B. If a thread is blocked in the wait method of an object, and another thread executes the notify method on the same object, it is still possible that the first thread might never resume execution.
- C. If a thread is blocked in the wait method of an object, and another thread executes the notify method on the same object, then the first thread definitely resumes execution as a direct and sole consequence of the notify call.
- D. If two threads are blocked in the wait method of one object, and another thread executes the notify method on the same object, then the first thread that executed the wait call first definitely resumes execution as a direct and sole consequence of the notify call. Discuss
- 10. What will be the output of the program?
public class Test { public static void main(String args[]) { class Foo { public int i = 3; } Object o = (Object)new Foo(); Foo foo = (Foo)o; System.out.println("i = " + foo.i); } }
Options- A. i = 3
- B. Compilation fails.
- C. i = 5
- D. A ClassCastException will occur. Discuss
More questions
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:
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:
Correct Answer: Assertion expressions should not contain side effects.
Explanation:
Assertion checking may be disabled for increased performance. Typically, assertion checking is enabled during program development and testing and disabled for deployment.
Option B is wrong. Because you assert that something is "true". True is Boolean. So, an expression must evaluate to Boolean, not int or byte or anything else. Use the same rules for an assertion expression that you would use for a while condition.
Option C is wrong. Usually, enforcing a precondition on a public method is done by condition-checking code that you write yourself, to give you specific exceptions.
Option D is wrong. "You're never supposed to handle an assertion failure"
Not all legal uses of assertions are considered appropriate. As with so much of Java, you can abuse the intended use for assertions, despite the best efforts of Sun's Java engineers to discourage you. For example, you're never supposed to handle an assertion failure. That means don't catch it with a catch clause and attempt to recover. Legally, however, AssertionError is a subclass of Throwable, so it can be caught. But just don't do it! If you're going to try to recover from something, it should be an exception. To discourage you from trying to substitute an assertion for an exception, the AssertionError doesn't provide access to the object that generated it. All you get is the String message.
Correct Answer: ABCdef
Explanation:
Line 2 returns a string object but does not change the originag string object s, so after line 2 s is still "ABC".
So what's happening on line 3? Java will treat line 3 like the following:
s = new StringBuffer().append(s).append("def").toString();
This effectively creates a new String object and stores its reference in the variable s, the old String object containing "ABC" is no longer referenced by a live thread and becomes available for garbage collection.
Correct Answer: Compilation fails.
Explanation:
Correct Answer: The elements in the collection are guaranteed to be unique.
Explanation:
Option A is wrong. HashSet makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time.
Option B is wrong. The set can be modified.
Option D is wrong. This is a Set and not a Map.
Correct Answer: NullPointerException at runtime
Explanation:
private static int[]x = new int[5];
private static int[x] declares a static i.e. class level array.
the "new" keyword is the word that actually creates said array.
int[5] in association with the new sets the size of the array. so since the above code contains no new or size decalarations when you try and access x[0] you are trying to access a member of an array that has been declared but not intialized hence you get a NullPointerException at runtime.
Correct Answer: same results 2 time(s)
Explanation:
Correct Answer: It will print the numbers 1 to 20 sequentially
Explanation:
The updating and output takes place inside synchronized code.
One thread will run to completion printing the numbers 1-10.
The second thread will then run to completion printing the numbers 11-20.
Correct Answer: If a thread is blocked in the wait method of an object, and another thread executes the notify method on the same object, it is still possible that the first thread might never resume execution.
Explanation:
Option A is incorrect - just because another thread activates the modify method in A this does not mean that the thread will automatically resume execution
Option C is incorrect - This is incorrect because as said in Answer B notify only wakes the thread but further to this once it is awake it goes back into the stack and awaits execution therefore it is not a "direct and sole consequence of the notify call"
Option D is incorrect - The notify method wakes one waiting thread up. If there are more than one sleeping threads then the choice as to which thread to wake is made by the machine rather than you therefore you cannot guarantee that the notify'ed thread will be the first waiting thread.
Correct Answer: i = 3
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