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- Question
Which is the valid declarations within an interface definition?
Options- A. public double methoda();
- B. public final double methoda();
- C. static void methoda(double d1);
- D. protected void methoda(double d1);
- Correct Answer
- public double methoda();
ExplanationOption A is correct. A public access modifier is acceptable. The method prototypes in an interface are all abstract by virtue of their declaration, and should not be declared abstract.Option B is wrong. The final modifier means that this method cannot be constructed in a subclass. A final method cannot be abstract.
Option C is wrong. static is concerned with the class and not an instance.
Option D is wrong. protected is not permitted when declaring a method of an interface. See information below.
Member declarations in an interface disallow the use of some declaration modifiers; you cannot use transient, volatile, or synchronized in a member declaration in an interface. Also, you may not use the private and protected specifiers when declaring members of an interface.
Language Fundamentals problems
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- 1. Which three piece of codes are equivalent to line 3?
- final int k = 4;
- public int k = 4;
- static int k = 4;
- abstract int k = 4;
- volatile int k = 4;
- protected int k = 4;
public interface Foo { int k = 4; /* Line 3 */ }
Options- A. 1, 2 and 3
- B. 2, 3 and 4
- C. 3, 4 and 5
- D. 4, 5 and 6 Discuss
Correct Answer: 1, 2 and 3
Explanation:
(1), (2) and (3) are correct. Interfaces can have constants, which are always implicitly public, static, and final. Interface constant declarations of public, static, and final are optional in any combination.- 2. Which one is a valid declaration of a boolean?
Options- A. boolean b1 = 0;
- B. boolean b2 = 'false';
- C. boolean b3 = false;
- D. boolean b4 = Boolean.false();
- E. boolean b5 = no; Discuss
Correct Answer: boolean b3 = false;
Explanation:
A boolean can only be assigned the literal true or false.- 3. 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 Discuss
Correct Answer: 0 to 65535
Explanation:
A char is really a 16-bit integer behind the scenes, so it supports 2 16 (from 0 to 65535) values.- 4. Which is a valid declarations of a String?
Options- A. String s1 = null;
- B. String s2 = 'null';
- C. String s3 = (String) 'abc';
- D. String s4 = (String) '\ufeed'; Discuss
Correct Answer: String s1 = null;
Explanation:
Option A sets the String reference to null.Option B is wrong because null cannot be in single quotes.
Option C is wrong because there are multiple characters between the single quotes ('abc').
Option D is wrong because you can't cast a char (primitive) to a String (object).
- 5. Which is a valid keyword in java?
Options- A. interface
- B. string
- C. Float
- D. unsigned Discuss
Correct Answer: interface
Explanation:
interface is a valid keyword.Option B is wrong because although "String" is a class type in Java, "string" is not a keyword.
Option C is wrong because "Float" is a class type. The keyword for the Java primitive is float.
Option D is wrong because "unsigned" is a keyword in C/C++ but not in Java.
- 6. 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.
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- 1. Which three piece of codes are equivalent to line 3?