Chapter 7

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 the method name and parameter list also called?

Answer 2

Method signature

Question 3

What are all access modifiers?

Answer 3

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

Question 4

What are all optional specifiers?

Answer 4

• 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 5

What are the rules for method names?

Answer 5

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 6

What is the difference between an array and varargs?

Answer 6

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

Question 7

What is the scope of the private access modifier?

Answer 7

Only accessible within the same class

Question 8

What is the scope of the default access modifier?

Answer 8

Private plus other classes in the same package

Question 9

What is the scope of the protected access modifier?

Answer 9

Default access plus child classes

Question 10

What is the scope of the public access modifier?

Answer 10

Protected access plus other packages

Question 11

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 11

0 twice

page 267

Question 12

What does it mean when we say Java is a “pass-by-value” language?

Answer 12

This means that a copy of the variable is made and the method receives that copy. Assignments made in the method do not affect the caller.

Question 13

What is printed in the following code?

public static void main(String[] args) {
  String name = "Willie";
  speak(name);
  System.out.println(name);
}

public static void speak(String name) {
name = “Wulm”;
}

Answer 13

“Willie”

The variable assignment is only to the method parameter and doesn’t affect the caller.

Question 14

What are the rules for method overloading?

Answer 14

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

Question 15

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

Answer 15

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 16

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

Answer 16

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 17

Is this a valid overloaded method? why?

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

Answer 17

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) {}

(page 281)

Question 18

Is this a valid overloaded method?

public void walk(int[] ints) {}
public void walk(Integer[] integers) {}

Answer 18

yes.

They specify actual types and don’t participate in type erasure.

(page 282)

Question 19

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 19

1. String glide(int i, int i)
2. String glide(long i, long i)
3. String glide(Integer i, Integer i)
4. String glide(int… nums)

(page 282)

Question 20

Does the following code work?

public static void play(Long l) {}

play(4);

Answer 20

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.

(page 283)

Question 21

What does encapsulation mean?

Answer 21

Encapsulation means only methods in the class with the variables can refer to the instance variables. Callers are required to use these methods.

Question 22

What is a getter method also called?

Answer 22

Accessor method

Question 23

What is a setter method also called?

Answer 23

Mutator method

Question 24

Does the following code compile?

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

private static void test(double val) {}

Answer 24

Yes

Question 25

Does the following code compile?

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

private static void test(short val) {}

Answer 25

No:

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