Declarations And Access Control

Which is a valid declaration within an interface?

A:

public static short stop = 23;

B:

protected short stop = 23;

C:

transient short stop = 23;

D:

final void madness(short stop);

Answer: A

(A) is valid interface declarations.

(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.

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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?

A:

final

B:

static

C:

private

D:

protected

Answer: C

The private access modifier limits access to members of the same class.

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.

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Which two cause a compiler error?

float[ ] f = new float(3);
float f2[ ] = new float[ ];
float[ ]f1 = new float[3];
float f3[ ] = new float[3];
float f5[ ] = {1.0f, 2.0f, 2.0f};

A:

2, 4

B:

3, 5

C:

4, 5

D:

1, 2

Answer: D

(1) causes two compiler errors ( '[' expected and illegal start of expression) because the wrong type of bracket is used, ( ) instead of [ ]. The following is the correct syntax: float[ ] f = new float[3];

(2) causes a compiler error ( '{' expected ) because the array constructor does not specify the number of elements in the array. The following is the correct syntax: float f2[ ] = new float[3];

(3), (4), and (5) compile without error.

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Which of the following class level (nonlocal) variable declarations will not compile?

A:

protected int a;

B:

transient int b = 3;

C:

private synchronized int e;

D:

volatile int d;

Answer: C

Option C will not compile; the synchronized modifier applies only to methods.

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.

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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 {}

A:

1 and 4

B:

2 and 5

C:

3 and 6

D:

4 and 6

Answer: C

(3), (6). Both are legal class declarations.

(1) is wrong because a class cannot be abstract and finalâ€”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.

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Questions for: Declarations And Access Control