Java Data Types

Question 1

Equals method of a primitive wrapper class

Answer 1

1. symmetric => a.equals(b) returns same as b.equals(a)
2. transitive => if a.equals(b) and b.equals(c) return true, then a.equals(c) returns true.
3. reflexive => a.equals(a) return true.

Question 2

Boolean

constructors

Answer 2

Boolean class has two constructors - Boolean(String) and Boolean(boolean) . The String constructor allocates a Boolean object representing the value true if the string argument is not null and is equal, ignoring case, to the string “true”. Otherwise, allocate a Boolean object representing the value false.

Question 3

Final variable

Answer 3

Must be initialized either in an instance block or in a constructor.

Question 4

Modifiers

static and final

Answer 4

static and final are valid modifiers for both member field and method declarations within a class.

Question 5

Modifiers

transient and volatile

Answer 5

transient and volatile modifiers are only valid for member field declarations.

Question 6

Modifiers

abstract and native

Answer 6

abstract and native are only valid for member methods.