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- Question
Which statement is true?
class Test1 { public int value; public int hashCode() { return 42; } } class Test2 { public int value; public int hashcode() { return (int)(value^5); } }
Options- A. class Test1 will not compile.
- B. The Test1 hashCode() method is more efficient than the Test2 hashCode() method.
- C. The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
- D. class Test2 will not compile.
- Correct Answer
- The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
ExplanationThe so-called "hashing algorithm" implemented by class Test1 will always return the same value, 42, which is legal but which will place all of the hash table entries into a single bucket, the most inefficient setup possible.Option A and D are incorrect because these classes are legal.
Option B is incorrect based on the logic described above.
More questions
- 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 one of the following will declare an array and initialize it with five numbers?
Options- A. Array a = new Array(5);
- B. int [] a = {23,22,21,20,19};
- C. int a [] = new int[5];
- D. int [5] array; Discuss
Correct Answer: int [] a = {23,22,21,20,19};
Explanation:
Option B is the legal way to declare and initialize an array with five elements.Option A is wrong because it shows an example of instantiating a class named Array, passing the integer value 5 to the object's constructor. If you don't see the brackets, you can be certain there is no actual array object! In other words, an Array object (instance of class Array) is not the same as an array object.
Option C is wrong because it shows a legal array declaration, but with no initialization.
Option D is wrong (and will not compile) because it declares an array with a size. Arrays must never be given a size when declared.
- 3. What allows the programmer to destroy an object x?
Options- A. x.delete()
- B. x.finalize()
- C. Runtime.getRuntime().gc()
- D. Only the garbage collection system can destroy an object. Discuss
- delete() - Method in class java.io.File : Deletes the file or directory denoted by this abstract pathname.
- delete(int, int) - Method in class java.lang.StringBuffer : Removes the characters in a substring of this StringBuffer.
- delete(int, int) - Method in interface javax.accessibility.AccessibleEditableText : Deletes the text between two indices
- delete(int, int) - Method in class : javax.swing.text.JTextComponent.AccessibleJTextComponent; Deletes the text between two indices
Correct Answer: Only the garbage collection system can destroy an object.
Explanation:
Option D is correct. When an object is no longer referenced, it may be reclaimed by the garbage collector. If an object declares a finalizer, the finalizer is executed before the object is reclaimed to give the object a last chance to clean up resources that would not otherwise be released. When a class is no longer needed, it may be unloaded.Option A is wrong. I found 4 delete() methods in all of the Java class structure. They are:
None of these destroy the object to which they belong.
Option B is wrong. I found 19 finalize() methods. The most interesting, from this questions point of view, was the finalize() method in class java.lang.Object which is called by the garbage collector on an object when garbage collection determines that there are no more references to the object. This method does not destroy the object to which it belongs.
Option C is wrong. But it is interesting. The Runtime class has many methods, two of which are:
- 4. What will be the output of the program?
class A { public A(int x){} } class B extends A { } public class test { public static void main (String args []) { A a = new B(); System.out.println("complete"); } }
Options- A. It compiles and runs printing nothing
- B. Compiles but fails at runtime
- C. Compile Error
- D. Prints "complete" Discuss
Correct Answer: Compile Error
Explanation:
No constructor has been defined for class B therefore it will make a call to the default constructor but since class B extends class A it will also call the Super() default constructor.Since a constructor has been defined in class A java will no longer supply a default constructor for class A therefore when class B calls class A's default constructor it will result in a compile error.
- 5. What will be the output of the program?
boolean bool = true; if(bool = false) /* Line 2 */ { System.out.println("a"); } else if(bool) /* Line 6 */ { System.out.println("b"); } else if(!bool) /* Line 10 */ { System.out.println("c"); /* Line 12 */ } else { System.out.println("d"); }
Options- A. a
- B. b
- C. c
- D. d Discuss
Correct Answer: c
Explanation:
Look closely at line 2, is this an equality check (==) or an assignment (=). The condition at line 2 evaluates to false and also assigns false to bool. bool is now false so the condition at line 6 is not true. The condition at line 10 checks to see if bool is not true ( if !(bool == true) ), it isn't so line 12 is executed.- 6. What will be the output of the program?
class s1 extends Thread { public void run() { for(int i = 0; i < 3; i++) { System.out.println("A"); System.out.println("B"); } } } class Test120 extends Thread { public void run() { for(int i = 0; i < 3; i++) { System.out.println("C"); System.out.println("D"); } } public static void main(String args[]) { s1 t1 = new s1(); Test120 t2 = new Test120(); t1.start(); t2.start(); } }
Options- A. Compile time Error There is no start() method
- B. Will print in this order AB CD AB...
- C. Will print but not be able to predict the Order
- D. Will print in this order ABCD...ABCD... Discuss
Correct Answer: Will print but not be able to predict the Order
Explanation:
We cannot predict the order in which threads are going to run.- 7. What will be the output of the program?
class Exc0 extends Exception { } class Exc1 extends Exc0 { } /* Line 2 */ public class Test { public static void main(String args[]) { try { throw new Exc1(); /* Line 9 */ } catch (Exc0 e0) /* Line 11 */ { System.out.println("Ex0 caught"); } catch (Exception e) { System.out.println("exception caught"); } } }
Options- A. Ex0 caught
- B. exception caught
- C. Compilation fails because of an error at line 2.
- D. Compilation fails because of an error at line 9. Discuss
Correct Answer: Ex0 caught
Explanation:
An exception Exc1 is thrown and is caught by the catch statement on line 11. The code is executed in this block. There is no finally block of code to execute.- 8. What will be the output of the program?
class Test { public static void main(String [] args) { int x= 0; int y= 0; for (int z = 0; z < 5; z++) { if (( ++x > 2 ) && (++y > 2)) { x++; } } System.out.println(x + " " + y); } }
Options- A. 5 2
- B. 5 3
- C. 6 3
- D. 6 4 Discuss
Correct Answer: 6 3
Explanation:
In the first two iterations x is incremented once and y is not because of the short circuit && operator. In the third and forth iterations x and y are each incremented, and in the fifth iteration x is doubly incremented and y is incremented.- 9. Which of the following are true statements?
- The Iterator interface declares only three methods: hasNext, next and remove.
- The ListIterator interface extends both the List and Iterator interfaces.
- The ListIterator interface provides forward and backward iteration capabilities.
- The ListIterator interface provides the ability to modify the List during iteration.
- The ListIterator interface provides the ability to determine its position in the List.
Options- A. 2, 3, 4 and 5
- B. 1, 3, 4 and 5
- C. 3, 4 and 5
- D. 1, 2 and 3 Discuss
Correct Answer: 1, 3, 4 and 5
Explanation:
The ListIterator interface extends the Iterator interface and declares additional methods to provide forward and backward iteration capabilities, List modification capabilities, and the ability to determine the position of the iterator in the List.- 10. What will be the output of the program?
public class Test { public static void main (String[] args) { String foo = args[1]; String bar = args[2]; String baz = args[3]; System.out.println("baz = " + baz); /* Line 8 */ } }And the command line invocation:> java Test red green blue
Options- A. baz =
- B. baz = null
- C. baz = blue
- D. Runtime Exception Discuss
Correct Answer: Runtime Exception
Explanation:
When running the program you entered 3 arguments "red", "green" and "blue". When dealing with arrays in java you must remember ALL ARRAYS IN JAVA ARE ZERO BASED therefore args[0] becomes "red", args[1] becomes "green" and args[2] becomes "blue".When the program entcounters line 8 above at runtime it looks for args[3] which has never been created therefore you get an
ArrayIndexOutOfBoundsException at runtime.
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- 1. Which two are equal?