Java Programming - Declarations and Access Control

Answer: Option C

Explanation:

Access modifiers dictate which classes, not which instances, may access features.

Methods and variables are collectively known as members. Method and variable members are given access control in exactly the same way.

private makes a member accessible only from within its own class

protected makes a member accessible only to classes in the same package or subclass of the class

default access is very similar to protected (make sure you spot the difference) default access makes a member accessible only to classes in the same package.

public means that all other classes regardless of the package that they belong to, can access the member (assuming the class itself is visible)

final makes it impossible to extend a class, when applied to a method it prevents a method from being overridden in a subclass, when applied to a variable it makes it impossible to reinitialise a variable once it has been initialised

abstract declares a method that has not been implemented.

transient indicates that a variable is not part of the persistent state of an object.

volatile indicates that a thread must reconcile its working copy of the field with the master copy every time it accesses the variable.

After examining the above it should be obvious that the access modifier that provides the most restrictions for methods to be accessed from the subclasses of the class from another package is C - protected. A is also a contender but C is more restrictive, B would be the answer if the constraint was the "same package" instead of "any package" in other words the subclasses clause in the question eliminates default.

Answer: Option B

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.

Answer: Option A

Explanation:

(3) is correct because an abstract class doesn't have to implement any or all of its interface's methods. (4) is correct because the method is correctly implemented ((7 > 4) is a boolean).

(1) is incorrect because interfaces don't implement anything. (2) is incorrect because classes don't extend interfaces. (5) is incorrect because interface methods are implicitly public, so the methods being implemented must be public.

Answer: Option C

Explanation:

(1), (2) and (6) are valid array declarations.

Option (3) is not a correct array declaration. The compiler complains with: illegal start of type. The brackets are in the wrong place. The following would work: public int[ ] a

Option (4) is not a correct array declaration. The compiler complains with: ']' expected. A closing bracket is expected in place of the 3. The following works: private int a []

Option (5) is not a correct array declaration. The compiler complains with 2 errors:

']' expected. A closing bracket is expected in place of the 3 and

<identifier> expected A variable name is expected after a[ ] .

Answer: Option C

Explanation:

Option A and B are wrong because they use the default access modifier and the access modifier for the class is public (remember, the default constructor has the same access modifier as the class).

Option D is wrong. The void makes the compiler think that this is a method specification - in fact if it were a method specification the compiler would spit it out.