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- Question
Which of the following code fragments inserted, will allow to compile?
public class Outer { public void someOuterMethod() { //Line 5 } public class Inner { } public static void main(String[] argv) { Outer ot = new Outer(); //Line 10 } }
Options- A. new Inner(); //At line 5
- B. new Inner(); //At line 10
- C. new ot.Inner(); //At line 10
- D. new Outer.Inner(); //At line 10
- Correct Answer
- new Inner(); //At line 5
Explanation
Option A compiles without problem.Option B gives error - non-static variable cannot be referenced from a static context.
Option C package ot does not exist.
Option D gives error - non-static variable cannot be referenced from a static context.
- 1. Which is a valid declaration within an interface?
Options- A. public static short stop = 23;
- B. protected short stop = 23;
- C. transient short stop = 23;
- D. final void madness(short stop); Discuss
- 2. Given a method in a protected class, what access modifier do you use to restrict access to that method to only the other members of the same class?
Options- A. final
- B. static
- C. private
- D. protected
- E. volatile Discuss
- 3. Which of the following class level (nonlocal) variable declarations will not compile?
Options- A. protected int a;
- B. transient int b = 3;
- C. private synchronized int e;
- D. volatile int d; Discuss
- 4. When is the Float object, created in line 3, eligible for garbage collection?
public Object m() { Object o = new Float(3.14F); Object [] oa = new Object[l]; oa[0] = o; /* Line 5 */ o = null; /* Line 6 */ oa[0] = null; /* Line 7 */ return o; /* Line 8 */ }
Options- A. just after line 5
- B. just after line 6
- C. just after line 7
- D. just after line 8 Discuss
- 5. Where will be the most chance of the garbage collector being invoked?
class HappyGarbage01 { public static void main(String args[]) { HappyGarbage01 h = new HappyGarbage01(); h.methodA(); /* Line 6 */ } Object methodA() { Object obj1 = new Object(); Object [] obj2 = new Object[1]; obj2[0] = obj1; obj1 = null; return obj2[0]; } }
Options- A. After line 9
- B. After line 10
- C. After line 11
- D. Garbage collector never invoked in methodA() Discuss
- 6. Which is valid in a class that extends class A?
class A { protected int method1(int a, int b) { return 0; } }
Options- A. public int method1(int a, int b) {return 0; }
- B. private int method1(int a, int b) { return 0; }
- C. public short method1(int a, int b) { return 0; }
- D. static protected int method1(int a, int b) { return 0; } Discuss
- 7. What is the most restrictive access modifier that will allow members of one class to have access to members of another class in the same package?
Options- A. public
- B. abstract
- C. protected
- D. synchronized
- E. default access Discuss
- 8. Which of the following is/are legal method declarations?
- protected abstract void m1();
- static final void m1(){}
- synchronized public final void m1() {}
- private native void m1();
Options- A. 1 and 3
- B. 2 and 4
- C. 1 only
- D. All of them are legal declarations. Discuss
- 9. Which two of the following are legal declarations for nonnested classes and interfaces?
- final abstract class Test {}
- public static interface Test {}
- final public class Test {}
- protected abstract class Test {}
- protected interface Test {}
- abstract public class Test {}
Options- A. 1 and 4
- B. 2 and 5
- C. 3 and 6
- D. 4 and 6 Discuss
- 10. Which three are valid method signatures in an interface?
- private int getArea();
- public float getVol(float x);
- public void main(String [] args);
- public static void main(String [] args);
- boolean setFlag(Boolean [] test);
Options- A. 1 and 2
- B. 2, 3 and 5
- C. 3, 4, and 5
- D. 2 and 4 Discuss
Declarations and Access Control problems
Search Results
Correct Answer: public static short stop = 23;
Explanation:
(B) and (C) are incorrect because interface variables cannot be either protected or transient. (D) is incorrect because interface methods cannot be final or static.
Correct Answer: private
Explanation:
Option A, B, D, and E are wrong because protected are the wrong access modifiers, and final, static, and volatile are modifiers but not access modifiers.
Correct Answer: private synchronized int e;
Explanation:
Option A and B will compile because protected and transient are legal variable modifiers. Option D will compile because volatile is a proper variable modifier.
Correct Answer: just after line 7
Explanation:
Option A is wrong. This simply copies the object reference into the array.
Option B is wrong. The reference o is set to null, but, oa[0] still maintains the reference to the Float object.
Option C is correct. The thread of execution will then not have access to the object.
Correct Answer: Garbage collector never invoked in methodA()
Explanation:
Option D is correct. Garbage collection takes place after the method has returned its reference to the object. The method returns to line 6, there is no reference to store the return value. so garbage collection takes place after line 6.
Option A is wrong. Because the reference to obj1 is stored in obj2[0]. The Object obj1 still exists on the heap and can be accessed by an active thread through the reference stored in obj2[0].
Option B is wrong. Because it is only one of the references to the object obj1, the other reference is maintained in obj2[0].
Option C is wrong. The garbage collector will not be called here because a reference to the object is being maintained and returned in obj2[0].
Correct Answer: public int method1(int a, int b) {return 0; }
Explanation:
Option A is correct - because the class that extends A is just simply overriding method1.
Option B is wrong - because it can't override as there are less access privileges in the subclass method1.
Option C is wrong - because to override it, the return type needs to be an integer. The different return type means that the method is not overriding but the same argument list means that the method is not overloading. Conflict - compile time error.
Option D is wrong - because you can't override a method and make it a class method i.e. using static.
Correct Answer: default access
Explanation:
Option A and C are wrong because public and protected are less restrictive. Option B and D are wrong because abstract and synchronized are not access modifiers.
Correct Answer: All of them are legal declarations.
Explanation:
Correct Answer: 3 and 6
Explanation:
(1) is wrong because a class cannot be abstract and final?there would be no way to use such a class. (2) is wrong because interfaces and classes cannot be marked as static. (4) and (5) are wrong because classes and interfaces cannot be marked as protected.
Correct Answer: 2, 3 and 5
Explanation:
(1), is incorrect because an interface method must be public; if it is not explicitly declared public it will be made public implicitly. (4) is incorrect because interface methods cannot be static.
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