lecture 10 - Enumerate , Java doc and annotations

Question 1

What is enum?

Answer 1

type/class is a special reference type that holds a set of predefined constants.

We don’t instantiate an enumerated class. Instead, get one pre-allocated fixed instance via ClassName.VALUE NAME

Java’s enum type can behave like normal classes, and can have
other attributes and methods in addition to their fixed values.

Question 2

Enum example

Answer 2

enum Day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY
}

Question 3

enum convention

Answer 3

By convention, the variable names are all capitalised.

All constants defined in an enum type are implicitly public static final.

Question 4

How are comments upported in java ?

Answer 4

single line comment // …
multiple lines comment /* … */
documentation comment /** … */

Question 5

What happens to the comments during compilation?

Answer 5

During compilation, all the comments are ignored.

Question 6

What is Javadoc?

Answer 6

A JDK tool automatically creates fancy HTML-based

documentation based on /** …*/ in your source files.

Question 7

You can include special doc tags in the documentation comments that provide specific information used by JavaDoc to format the documentation pages. What are these tags ?

Answer 7

@author Provides information about the author.
@version Indicates the version number.
@since Indicate the version.
@param Provides the name and description of a method.
@return Provides a description of a method’s return value.
@throws Indicates exceptions that are thrown by a method.

Question 8

What is the difference between simple comment and annotations ?

Answer 8

An annotation always starts with the symbol @ followed by the annotation name.

Annotations are checked by Java
compiler. (Different from the doc tag)

Question 9

Predefined annotations ?

Answer 9

@Deprecated
@Override
@SuppressWarnings
Custom annotations could be defined by using @interface

Question 10

What does the @Deprecated tag mean ?

Answer 10

@Deprecated - indicates a marked element should no longer be used. It is usually also documented using the Javadoc @deprecated tag

/**
* @deprecated ← a doc tag, not checked by compiler
* explanation of why it was deprecated
*/
@Deprecated ← an annotation, checked by compiler
void anyMethod() { … }

Question 11

What does the override tag stand for ?

Answer 11

@Override - informs the compiler that the element is meant tooverride an element declared in a superclass.

@Override
void overridingMethod() { }

If the method is not an overriding method, an error will be generated during compilation:
error: method does not override or implement a method from a supertype

Question 12

What doe the predefined tag suppress warnings stand for ?

Answer 12

@SuppressWarnings - tells the compiler to suppress specific warnings.

@SuppressWarnings(”unchecked”)
@SuppressWarnings(”deprecation”)

@SuppressWarnings(“deprecation”)
_____void myMethod() {
________myObject.deprecatedMethod();
}