Which three piece of codes are equivalent to line 3?

1. final int k = 4;
2. public int k = 4;
3. static int k = 4;
4. abstract int k = 4;
5. volatile int k = 4;
6. protected int k = 4;

public interface Foo 
{ 
    int k = 4; /* Line 3 */
}

Option 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.

A boolean can only be assigned the literal true or false.

A char is really a 16-bit integer behind the scenes, so it supports 2 ¹⁶ (from 0 to 65535) values.

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).

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.