Ch7 Methods and Encapsulation

Question 1

Name all components in the following method declaration:

public final void nap(int minutes) throws InterruptedException {}

Answer 1

• Access modifier
• Optional specifier
• Return type
• Method name
• Parantheses
• Parameter(s)
• Exception
• Method body

Question 2

What are all access modifiers?

Answer 2

• Private
• Default (Package-private)
• Protected
• Public

Question 3

What are all optional specifiers?

Answer 3

• static
• abstract (when a method body is not provided)
• final (used when a method is not allowed to be overridden)
• synchronized (used with multithreaded code)
• native (not on exam)
• strictfp (not on exam)

Question 4

What are the rules for method names?

Answer 4

Same as variable names

• Can contain letters, numbers, underscore and $
• Cannot start with a number
• Cannot be a reserved word
• Single underscore is not allowed

Question 5

What is the difference between an array and varargs?

Answer 5

Varargs have one additional rule in that it must be the last element in a method’s parameter list.

Question 6

What is the scope of the default access modifier?

Answer 6

Private plus other classes in the same package

Question 7

What does the following code print?

public class Koala {
public static int count = 0;
}
class TestKoala {
public static void main(String[] args) {
Koala k = new Koala();
System.out.println(k.count);
k = null;
System.out.println(k.count);
}
}

Answer 7

0 twice

Question 8

What are the rules for method overloading?

Answer 8

• The method must have an equal name
• The method must have different parameters (different type(s) or more parameters)
• Everything else can vary

Question 9

Can I overload a method with an array parameter with a method with a varargs parameter?

Answer 9

No. Java treats varargs as if they were an array. You can pass an array to one of the methods and Java would not know which method to call.

Question 10

Can I overload a method with a primitve type parameter with a method with its corresponding wrapper class type parameter?

Answer 10

Yes. Java tries to use the most specific parameter it can find. If the primitive int method version is not present, it will autobox to the method with the wrapper class type parameter.

Question 11

Is this a valid overloaded method? why?

public void walk(List< String> strings) {}
public void walk(List< Integer> integers) {}

Answer 11

no.

Java has a concept called type erasure where generics are used only at compile time. That means the compiled code looks like this:

public void walk(List strings) {}
public void walk(List integers) {}

Question 12

What is the order Java uses to choose the right overloaded method given the following command glide(1, 2) and the following methods:

String glide(Integer i, Integer i)
String glide(int i, int i)
String glide(long i, long i)
String glide(int… nums)

Answer 12

String glide(int i, int i)
String glide(long i, long i)
String glide(Integer i, Integer i)
String glide(int… nums)

Question 13

Does the following code work?

public static void play(Long l) {}

play(4);

Answer 13

No.

Java is happy to convert the int 4 to a long 4 or an Integer 4 (autoboxing). It cannot handle converting to a long and then to a Long.

Question 14

Does the following code compile?

public static void main(String[] args) {
test(1);
}

private static void test(double val) {}

Answer 14

Yes

Question 15

Does the following code compile?

public static void main(String[] args) {
test(1);
}

private static void test(short val) {}

Answer 15

No:

error: incompatible types: possible lossy conversion from int to short