Chapter 4

Front 1

Is the following a valid method signature?

public final void nap (int minutes) throws InterruptedException {

// code code code

}

Back 1

Yes, it is valid.

public and final are optional

the exception is also optional

return type is required (right before method name)

method name and ( ) are required.

Front 2

Is the following a valid method signature?

void public walk()

Back 2

No, the return type must be written right before method name.

Front 3

Is the following a valid method signature?

public final void walk(){

}

Back 3

yes, it's valid.

there is no return, though one could include "return; " (which is returning nothing)

Front 4

Is the following a valid method signature?

public void final walk() {

}

Back 4

No, not valid

return type must be written directly before method name

Front 5

Is the following valid?

public walk(){

}

Back 5

No, it's missing a return type

Front 6

Will the following compile?

private final String walk ( int a ){

if ( a == 4 ) return "";

}

Back 6

No

The signature is ok, but if a is not 4, the method won't return anything. This method must always return a String to be valid.

Front 7

Is this valid?

public void 2walk(){

}

Back 7

No

The method name (identifier) may only contain letters, numbers, $ or _. Reserved words are not allowed (but capitalizing them is fine.)

The identifier may start with a letter $ or _, but not a number.

Front 8

Is this valid?

public final Int walk_$$(){

return 3;

}

Back 8

No

The return type is invalid. You could return Integer - which is the wrapper object, or int.

the method name is legal

Front 9

Is this valid?

public String walk {

return "123";

}

Back 9

No

Methods must have ( ) after their identifier (method name)

Front 10

Is this valid?

void walk(int ... nums, int start) { }

Back 10

No

Varargs must be listed last in a parameter list

Front 11

Is this valid?

void walk(int ... start, int ... nums) { }

Back 11

No

Only one varags is allowed and it must be listed last in the parameter list.

Front 12

Is this valid?

void walk ( int start, int... nums) { }

Back 12

Yes

one varags is allowed and it is listed last in the parameter list.

Front 13

What does the following return?

public static void walk (int start, int ... nums) {

System.out.prinln(nums.length); }

walk(1);

walk(1,2);

walk(1,2,3);

walk(1,[2,3,4]);

walk(1, new int[] {4,5,6} );

Back 13

public static void walk (int start, int ... nums) { System.out.prinln(nums.length); }

walk(1); // 0

walk(1,2); // 1

walk(1,2,3); // 2

walk(1,[2,3,4]); //3

walk(1, new int[] {4,5,6} ); // 3

Front 14

Is this valid?

walk(int[] start, ...int nums ) { }

Back 14

No

The ... must be AFTER the type, not before it.

Front 15

Is the following valid?

walk(1, { 2,3 } );

public static void walk (int start, int ... nums) { System.out.prinln(nums.length); }

Back 15

No.

The array within the method call is not properly defined

Front 16

Define the scope of a private class member

Back 16

Only available within declared class

Front 17

Define the scope of a package private class member (default access)

Back 17

Available within declared class AND

classes within the same package

Front 18

Define the scope of a protected class member

Back 18

Available within declared class AND

classes within same package AND

within child classes (sub-classes) in a different package (using the reserved work "extends")

Front 19

Define the scope of a public class member

Back 19

Available to all classes and all class members

Front 20

Can a static class member use an instance class member? Explain how it may/may not be possible

Back 20

No.

Only an instance method can call another instance method on the same class without using a reference variable.

Instance members require an object, static members are linked to a classname, not an object.

page 82-84

Front 21

Can an instance class member use/call a static class member? Explain how it may/may not be possible

Back 21

Yes. The compiler checks for the type of the reference and uses that instead of the object.

example:

static count = 0;

// Reference k = new Object()

Koala k = new Koala();

k = null;

// java doesn't care that k is null, it's reference (object) is still Koala.

System.out.println( k.count ); //prints 0

page 82-84

Front 22

Can a static method call another static method or variable? Explain how it may/may not be possible

Back 22

Yes

It uses the specific classname to do so if the member is not in the calling class

page 82-84

Front 23

Can a static method call an instance method or variable? Explain how it may/may not be possible

Back 23

Not really.

You could use they keyword new to create an object (instantiate) from a static method (such as in the main method of a class).

Only an instance method can call another instance method on the same class without using a reference variable.

page 82-84

Front 24

Can an instance method call a static method or variable?

Back 24

Yes

It uses the classname or a reference (object) variable to do so

page 82-84

Front 25

Can an instance method call another instance method or variable?

Back 25

Yes

It must use a reference (object) variable to do so.

page 82-84

Front 26

Define a final variable and it's naming convention

Back 26

It is a variable that cannot be changed, a constant.

Proper naming uses all uppercase letters with _ between words.

public static final int NUM_BUCKETS = 5;

Front 27

Is this a valid import statement?

import static java.util.Arrays;

Back 27

No -- you can't statically import a class.

a valid import would be :

import static java.util.Arrays.asList;

Front 28

Is this a valid import statement?

static import java.util.Arrays.asList;

Back 28

No -- import must be listed first in the statement

Front 29

Is this proper implementation?

import static java.util.Arrays.asList;

.

.

Arrays.asList("one");

Back 29

No. The Array class was not imported -- only .asList was imported.

valid code would be simply

" asList("one"); "

Front 30

Explain what is to be expected when methods pass variables back and forth.

(how is data affected?)

Back 30

Assignments made in the method do not affect the caller.

References are passed back and forth - the objects those references point to are not passed.

Remember immutability when passing values. If a new object is assigned to the reference, the parameter accepted is changed locally, but not updated outside of that method.

StringBuilder and ArrayList have methods that change the object itself. The reference never changes so the caller IS changed outside of the local method.

Front 31

Explain the order Java uses when selecting which overloaded method to execute

Back 31

Specific ---> non- specific

Exact match by type -- int

Larger primitive type -- long

Autoboxed type -- Integer

Varargs -- int ... nums

** will only do one conversion

int --> Integer object is ok

int --> Long object is not ok.

Front 32

What is the valid syntax for a constructor signature?

Back 32

A constructor must match the name of the class (case-sensitive) and have no return type.

Front 33

Is the following a valid constructor?

public Hamster (int weight) {

System.out.println("in constructor");

// ready to call this!

this(weight, "brown");

}

public Hamster (int weight, String color){

this.weight = weight;

this.color = color;

}

Back 33

No. If the keyword this() is used to call another constructor, it must be the first non-comment in the code block.

Front 34

Where can final instance variables be initialized?

(check all that apply)

A. Any place is fine, as long as it's done only once

B. In a Static code block

C. In an Instance initializer

D. In a constructor

Back 34

C. In an Instance initializer

D. In a constructor

Front 35

What is the order of initialization?

Back 35

Superclass --> Static --> Instance --> Constructor

All fields are instantiated in the order that they appear in the file. (while still following the type order of initialization of course)

Front 36

What are the rules for JavaBeans naming conventions?

Back 36

1. Properties are private

2. Getter methods begin with get (or is if property is boolean)

3. Setter methods begin with set

4. The method name must include the property being access in the following way

void setNumEggs(int num);

int getNumEggs();

Front 37

What is encapsulation?

Back 37

Encapsulation prevents callers from making uncontrolled changes to your class.

Only methods in the class with the variables can refer to the instance variables.

Front 38

What is needed to create an immutable class?

Back 38

Immutable classes have no setters. They use constructors to create a new object.

Send a copy of the object passed in by using the keyword new (within a getter or a constructor):

public StringBuilder getBuilder(){

return new StringBuilder(builder);

}

OR return an immutable object.

public String get Value(){

return builder.toString;

}

Front 39

What is the short version of the following?

(Animal a) -> { return a.canHop(); }

Back 39

a -> a.canHop()

Front 40

Is the following a valid lambda expression?

print( a -> { a.startsWith("test"); } );

Back 40

No

It's missing a return statement.

print( a -> { return a.startsWith("test"); } );

Front 41

Is the following a valid lambda expression?

print ( Animal a -> a.startsWith("test") );

Back 41

No

The first parameter needs parenthesis because the type is included.

print ( (Animal a) -> a.startsWith("test") );

Front 42

Assume there are valid interfaces that can consume a lambda with zero, one, or two String parameters.

Which of the following is invalid?

A. print ( ( ) -> true);

B. print ( a -> a.startsWith("test") );

C. print ( (String a, String b) -> a.startsWith(b) );

D. print ( a, b -> a.startsWith(a) );

Back 42

D is invalid because it neglected parenthesis around the two input values.

the correct syntax is...

print ( ( a, b ) -> a.startsWith(a) );

Front 43

Which of the following is invalid?

A. ( a, b ) -> { int a = 0; return 5;}

B. ( a, b ) -> {int c = 0; return 5;}

Back 43

A -- Java will not allow local variables to be redeclared.

It's perfectly legal to declare a new variable and not use the first two parameters.

Front 44

What import statement is needed to use the interface Predicate?

Back 44

java.util.function.Predicate

or

java.util.function

Front 45

Explain the test() method in the Predicate interface

Back 45

It is a method that takes any one reference type (similar to how ArrayList can accept any one reference type) and returns a boolean.

example

private void print(List animals, Predicate checker);

Front 46

Explain ArrayList's removeIf() method

Back 46

It is a method that takes a lambda expression (a predicate) and removes all elements in the ArrayList that match the boolean check defined.

example:

List bunnies = new ArrayList<>( );

bunnies.removeIf( s -> s.charAt(0) != 'h' );