Ch 4 - Methods and Encapsulation

Question 1

Which of the following methods compile?

public void walk1() {}

public void walk2() { return; }

public String walk3() {}

Answer 1

public void walk1() {}

public void walk2() { return; }

public String walk3() {} – does not compile

Question 2

What optional specifier is used when not providing a method body?

Answer 2

abstract

Question 3

When a method is defined as public, where can it be called from?

Answer 3

Any class

Question 4

Which of the following lines below do not compile:

public void walk1() {}

default void walk2() {}

void public walk3() {}

void walk4() {}

Answer 4

public void walk1() {}

default void walk2() {} – does not compile

void public walk3() {} – does not compile

void walk4() {}

Question 5

What optional specifier is used for defining class methods?

Answer 5

static

Question 6

Which of the following method signatures do not compile?

public void walk1() {}

public final void walk2() {}

public static final void walk3() {}

public final static void walk4() {}

public modifier void walk5() {}

public void final walk6() {}

final public void walk7() {}

Answer 6

public void walk1() {}

public final void walk2() {}

public static final void walk3() {}

public final static void walk4() {}

public modifier void walk5() {} – does not compile

public void final walk6() {} – does not compile

final public void walk7() {}

Question 7

When a method is defined as protected, where can it be called from?

Answer 7

Can only be called from classes in the same package or subclasses.

Question 8

Describe the different parts of the method signature and identify which are required and which aren’t.

Answer 8

Access modifier (public/private) - not required

optional specifier (final) - not required

return type (void) - required

method name (nap) - required

parameter list (int minutes) - required but can be empty parenthesis

optional exception list (throws Exception) - not required

method body ({}) - required, but can be empty

Question 9

When a method is defined as private, where can it be called from?

Answer 9

Only from within the same class

Question 10

When a method is defined as Default package protected, where can it be called from?

Answer 10

Can only be called from classes in the same package.

Question 11

Which of the following methods compile?

public String walk1 { return “”; }

public walk2() {}

String walk3(int a) { if (a == 4) return “”; }

Answer 11

public String walk1 { return “”; }

public walk2() {} – does not compile

String walk3(int a) { if (a == 4) return “”; } – does not compile

Question 12

true/false, a method signature does not have to provide a return type.

Answer 12

false. If there is not return type provided by the method, you must use the ‘void’ key word in the signature.

Question 13

When a method returns a value, it must be assignable to…

Answer 13

…the return type.

Question 14

Name the four access modifiers for methods.

Answer 14

public

private

protected

Default (package protected)

Question 15

What optional specifier is used when a method is not allowed to be overridden by a subclass?

Answer 15

final

Question 16

true/false, the following code compiles:

package pond.duck;

public class ParentDuck {

String noise = “quack”;

void quack() { System.out.println(noise); }

private void makeNoise() { quack();

}}

package pond.duck;

public class Duckling {

public void makeNoise() {

ParentDuck duck = new ParentDuck();

duck.quack();

System.out.println(duck.noise);

}}

Answer 16

true

Question 17

What is the output of the following code?

public static void run(int… nums) {

System.out.println(nums[1]);

}

public static void main(String[] args) {

run(11, 22);

}

Answer 17

22

Question 18

Which of the following methods will compile?

public void walk1(int… nums) {}

public void walk2(int start, int… nums) {}

public void walk3(int… nums, int start) {}

public void walk4(int… start, int… nums) {}

Answer 18

public void walk1(int… nums) {}

public void walk2(int start, int… nums) {}

public void walk3(int… nums, int start) {} // does not compile

public void walk4(int… start, int… nums) {} // does not compile

Question 19

What would the output of the following program be?

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

System.out.println(nums.length);

}

public static void main(String[] args) {

walk(1);

walk(1, 2);

walk(1, 2, 3);

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

walk(1, null);

}

Answer 19

0

1

2

2

NullPointerException

Question 20

When using a vararg parameter in a method’s input parameter list, where must it be located?

Answer 20

It must be the last element.

Question 21

Which of the following methods compile?

public void walk1() {}

public void 2walk() {}

public walk3 void() {}

public void Walk_$() {}

public void() {}

Answer 21

public void walk1() {}

public void 2walk() {} – does not compile

public walk3 void() {} – does not compile

public void Walk_$() {}

public void() {} – does not compile

Question 22

Which of the following methods compile?

public void walk1() {}

public void walk2();

public void walk3(int a) { int name = 5; }

Answer 22

public void walk1() {}

public void walk2(); – does not compile

public void walk3(int a) { int name = 5; }

Question 23

true/false, the following code compiles:

package pond.duck;

public class ParentDuck {

private String noise = “quack”;

private void quack() { System.out.println(noise); }

private void makeNoise() { quack();

}}

package pond.duck;

public class Duckling {

public void makeNoise() {

ParentDuck duck = new ParentDuck();

duck.quack(); System.out.println(duck.noise);

}}

Answer 23

false

Question 24

How many exceptions can you put in the optional exception list?

Answer 24

As many as you want.

Question 25

Which of the following methods compile?

public void walk1() {}

public void walk2 {}

public void walk3(int a) {}

public void walk4(int a; int b) {}

public void walk5(int a, int b) {}

Answer 25

public void walk1() {}

public void walk2 {} – does not compile

public void walk3(int a) {}

public void walk4(int a; int b) {} – does not compile

public void walk5(int a, int b) {}

Question 26

How many vararg parameters can you have in a method’s input parameters list?

Answer 26

only one

Question 27

true/false, the following code compiles:

package pond.duck;

public class ParentDuck {

String noise = “quack”;

void quack() {

System.out.println(noise);

}

private void makeNoise() {

quack();

}}

package pond.swan;

import pond.duck.ParentDuck;

public class Cygnet {

public void makeNoise() {

ParentDuck duck = new ParentDuck();

duck.quack();

System.out.println(duck.noise);

}}

Answer 27

false

Question 28

The protected access modifier adds the ability to what?

Answer 28

Access members of a parent class.

Question 29

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.inland;

import pond.shore.Bird;

public class Bird2 {

public void watchBird() {

Bird bird = new Bird();

bird.floatInWater();

System.out.println(bird.text);

}}

Answer 29

false, protected members are only visible to sub classes and classes in the same package.

Question 30

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.swan;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void swim() {

floatInWater();

System.out.println(text);

}}

Answer 30

true

Question 31

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.goose;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void swim() {

Bird2 other = new Bird2();

other.floatInWater();

System.out.println(other.text);

}}

package pond.duck;

import pond.goose.Bird2;

public class Bird3 {

public void watch() {

Bird2 bird2 = new Bird2();

bird2.floatInWater();

}}

Answer 31

false

Question 32

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.swan;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void swim() {

Bird2 other = new Bird2();

other.floatInWater();

System.out.println(other.text);

}}

Answer 32

true

Question 33

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.goose;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void watchBird() {

floatInWater();

System.out.println(text);

}}

Answer 33

true, Bird2 is a subclass of Bird.

Question 34

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.goose;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void swim() {

Bird2 other = new Bird2();

other.floatInWater();

System.out.println(other.text);

}

pubic void swim2() {

Bird other = new Bird2();

other.floatInWater();

System.out.println(other.text);

}}

Answer 34

false.

Question 35

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.shore;

public class Bird2 {

public void watchBird() {

Bird bird = new Bird();

bird.floatInWater();

System.out.println(bird.text);

}}

Answer 35

true, Bird2 is in the same package as Bird.

Question 36

true/false, the following code compiles:

package pond.shore;

public class Bird {

protected String text = “floating”;

protected void floatInWater() {

System.out.println(text);

}}

package pond.swan;

import pond.shore.Bird;

public class Bird2 extends Bird {

public void swim() {

Bird other = new Bird();

other.floatInWater();

System.out.println(other.text);

}}

Answer 36

false. The code does not compile because the members of Bird are not being accessed in Bird2 via inheritance.

Question 37

true/false, a static method can call an instance method or member.

Answer 37

false Well, it can if the method instantiates the object.

Question 38

What is the output of the following lines of code?

public class Counter {

private static int count;

public Counter() { count++; }

public static void main(String[] args) {

Counter c1 = new Counter();

Counter c2 = new Counter();

Counter c3 = new Counter();

System.out.println(count);

}}

Answer 38

3

Question 39

true/false, a static member can call an instance member.

Answer 39

false

Question 40

true/false, the following code will compile:

package pond.duck;

public class Bird {

public String name = “helpful”;

public void swim() {

System.out.println(“swim”);

}}

package pond.goose;

import pond.duck.Bird;

public class Goose {

public void swim() {

Bird bird = new Bird();

bird.swim();

System.out.println(bird.name);

}}

Answer 40

true

Question 41

What is the output of the following code?

public class Koala {

public static int count = 0;

}

public class KoalaTester {

public static void main(String[] args) {

Koala k = new Koala();

System.out.println(k.count);

k = null;

System.out.println(k.count);

}}

Answer 41

0

0

Question 42

true/false, an instance method can call a static method or member.

Answer 42

true

Question 43

Does the following code compile, and if not, why?

public class Gorilla {

public static int count;

public static void addGorilla() { count++; }

public void babyGorilla() { count++; }

public void announceBabies() {

addGorilla();

babyGorilla();

}

public static void announceBabiesToEveryone() {

addGorilla();

babyGorilla();

}

public int total;

public static double average = total / count;

}

Answer 43

The code does not compile here:

public static void announceBabiesToEveryone() {

addGorilla();

babyGorilla(); // does not compile

}

It also does not compile on this line:

public static double average = total / count;

You cannot make a static reference to a non static member.

Question 44

Having a static method eliminates what?

Answer 44

…the need for the caller to instantiate the object just to call the method.

Question 45

When a member has default (package private) permissions, what does it mean?

Answer 45

It means that a member is private to classes in the same package. In other words, only classes in the same package can access it.

Question 46

true/false, a static method can call another static method or member.

Answer 46

true

Question 47

What is the output of the following code?

public class Koala {

public static int count = 0;

}

public class KoalaTester {

public static void main(String[] args) {

Koala.count = 4;

Koala k1 = new Koala();

Koala k2 = new Koala();

k1. count = 6;
k2. count = 5;

System.out.println(Koala.count);

}}

Answer 47

5

Question 48

What is the output of the following code?

public class Static {

private String name = “Static class”;

public static void first() {}

public static void second() {}

public static void third() {

System.out.println(name);

}

public static void main(String[] args) {

first();

second();

third();

}}

Answer 48

compiler error on this line:

public static void third { System.out.println(name); }

the variable name is not static.

Question 49

What is the output of the following code?

public class Static {

private String name = “Static class”;

public static void first() {}

public static void second() {}

public void third() {

System.out.println(name);

}

public static void main(String[] args) {

first();

second();

third();

}}

Answer 49

compiler error on this line:

third();

You cannot call a non static method from a static method, such as main.

Question 50

Does this code compile?

private static final ArrayList values = new ArrayList<>();

public static void main(String[] args) { values.add(“changed”); }

Answer 50

yes, “values” is a reference variable. All the compiler can do is make sure that we don’t try to reassign “values” to a different object.

Question 51

What are static imports used for?

Answer 51

Importing static members of classes.

Question 52

What is the output of the following code?

public class ReturningValues {

public static void main(String[] args) {

int number = 1;

String letters = “abc”;

number(number);

letters = letters(letters);

System.out.println(number + letters);

}

public static int number(int number) {

number++;

return number;

}

public static String letters(String letters) {

letters += “d”;

return letters;

}}

Answer 52

1abcd

Question 53

Does the following code compile?

import static statics.A.TYPE;

import static statics.B.TYPE;

Answer 53

No, you cannot import multiple static members with the same name.

Question 54

Which of the following lines of code do not compile?

import static java.util.Arrays;

import static java.util.Arrays.asList;

static import java.util.Arrays.*;

public class StaticImports {

public static void main(String[] args) {

Arrays.asList(“one”);

} }

Answer 54

import static java.util.Arrays; // does not compile. static imports are only for static class members, not classes

import static java.util.Arrays.asList;

static import java.util.Arrays.*; // does not compile. the terms static and import are in the wrong order

public class StaticImports {

public static void main(String[] args) {

Arrays.asList(“one”); // does not compile. Although we’ve statically imported asList, we haven’t imported Arrays.

} }

Question 55

true/false, you cannot initialize a static variable on the same line in which it’s declared.

Answer 55

false

Question 56

Does the following code compile?

private static final int NUM_SECONDS_PER_HOUR;

static {

int numSecondsPerMinute = 60;

int numMinutesPerHour = 60;

NUM_SECONDS_PER_HOUR = numSecondsPerMinute * numMinutesPerHour;

}

Answer 56

Yes, although NUM_SECONDS_PER_HOUR is final, the static initializer is the first assignment. Since it occurs upfront, it is ok.

Question 57

Does the following code compile?

private static int one;

private static final int two;

private static final int three = 3;

private static final int four;

static {

one = 1;

two = 2;

three = 3;

two = 4;

}

Answer 57

No, the following lines do not compile:

private static int one;

private static final int two;

private static final int three = 3;

private static final int four; // does not compile

static {

one = 1;

two = 2;

three = 3; // does not compile

two = 4; // does not compile

}

Question 58

What is the output of the following code?

public static void main(String[] args) {

String name = “Webby”;

speak(name);

System.out.println(name);

}

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

Answer 58

Webby

Question 59

Assigning a new primitive or reference to a parameter does or does not change the caller?

Answer 59

Does not

Question 60

Does the following code compile?

private static final int NUM_SECONDS_PER_HOUR;

static { int numSecondsPerMinute = 60;

int numMinutesPerHour = 60;

NUM_SECONDS_PER_HOUR = numSecondsPerMinute * numMinutesPerHour;

NUM_SECONDS_PER_HOUR = 100;

}

Answer 60

No. The first assignment of NUM_SECONDS_PER_HOUR is ok in the static initializer, but the second one is not.

Question 61

true/false, when using static imports, you can import multiple static methods or variables of the same name.

Answer 61

false.

Question 62

Does this code compile?

public class Initializers() {

private static final int NUM_BUCKETS = 45;

public static void main(String[] args) {

NUM_BUCKETS = 5;

} }

Answer 62

No, compiler error on this line:

NUM_BUCKETS = 5;

the error happens because the variable is labeled as final.

Question 63

What is the output of the following code?

public static void main(String[] args) {

StringBuilder name = new StringBuilder();

speak(name);

System.out.println(name);

}

public static void speak(StringBuilder s) {

s.append(“Webby”);

}

Answer 63

Webby

Question 64

true/false, you can use a static import to import a class.

Answer 64

false. A static import is only for importing static class members.

Question 65

What is the output of the following code?

public static void main(String[] args) {

int num = 4;

newNumber(num);

System.out.println(num);

}

public static void newNumber(int num) { num = 8; }

Answer 65

4

Question 66

Calling methods on a reference to an object does or does not affect the caller?

Answer 66

Does

Question 67

Does the following code compile?

public void fly(Integer numMiles) {}

fly(3);

Answer 67

Yes, through autoboxing

Question 68

What is method overloading?

Answer 68

When there are different method signatures with the same name but different type parameters.

Question 69

Consider the following two methods:

public void fly(int[] lengths) {}

public void fly(int… lengths) {}

Can you call each of them with the following lines?

fly(new int[] {1, 2, 3};

fly(1, 2, 3);

Answer 69

No. You can call either method with this line:

fly(new int[] {1, 2, 3};

But you can only call the varargs method with this line:

fly(1, 2, 3);

Question 70

Does the following code compile?

public void fly(int numMiles) {}

public int fly(int numMiles) {}

Answer 70

No. The return type does not make a difference on overloading methods.

Question 71

What is the output of the following code:

public class ReferenceTypes {

public void fly(String s) { System.out.print(“string “);

}

public void fly(Object o) { System.out.print(“object “); }

public static void main(String[] args) {

ReferenceTypes r = new ReferenceTypes();

r. fly(“test”);
r. fly(56);

}}

Answer 71

string object

Question 72

Does the following code compile?

public void fly(int[] lengths) {}

public void fly(int… lengths) {}

Answer 72

No. Because java treats varargs as an array, it considers these two methods to be the same.

Question 73

Consider the following two methods:

public void fly(int numMiles) {}

public void fly(Integer numMiles) {}

Which method will be used by the following line?

fly(3);

Answer 73

This method:

public void fly(int numMiles) {}

Question 74

Does the following code compile?

class Rabbit1 { }

class Rabbit2 { public Rabbit2() {} }

class Rabbit3 { public Rabbit3(boolean b) { } }

class Rabbit4 { private Rabbit4() {} }

public class RabbitsMultiply {

public static void main(String[] args) {

Rabbit1 r1 = new Rabbit1();

Rabbit2 r2 = new Rabbit2();

Rabbit3 r3 = new Rabbit3(true);

Rabbit4 r4 = new Rabbit4();

}}

Answer 74

No, this line produces a compiler error:

Rabbit4 r4 = new Rabbit4();

This is because the Rabbit4 class only has a private constructor.

Question 75

Inside a constructor, the “this” keyword tells Java what?

Answer 75

That you want to reference an instance variable.

Question 76

What happens if you do not create a constructor in your java classes?

Answer 76

Java will create a do-nothing one for you.

Question 77

When would you use only a private constructor?

Answer 77

When your class only has static methods.

Question 78

What is the output of the following code?

public class Conversions {

public static void play(Long l) { }

public static void play(Long… l) { }

public static void main(String[] args) {

play(4);

play(4L);

}}

Answer 78

Compiler error on this line:

play(4);

We can’t convert 4 to int, then to a long, and then to a Long (you can only convert once). The second line works because it is passing a long which is then converted to a Long:

play(4L);

Question 79

What is the output of the following code?

public class Plane {

public void fly(int l) { System.out.print(“int “); }

public static void main(String[] args) {

Plane p = new Plane();

p.fly(123L);

}}

Answer 79

Compiler error on this line:

p.fly(123L);

Question 80

What is the output of the following code?

public class Plane {

public void fly(int i) {

System.out.print(“int “);

}

public void fly(long l) { System.out.print(“long “); }

public static void main(String[] args) {

Plane p = new Plane();

p. fly(123);
p. fly(123L);

}}

Answer 80

int long

Question 81

When is the do-nothing constructor created for you?

Answer 81

At compile time.

Question 82

Which of the following classes get a default no-argument constructor created?

class Rabbit1 {}

class Rabbit2 { public Rabbit2() {} }

class Rabbit3 {public Rabbit3(boolean b) { } }

class Rabbit4 { private Rabbit4() { } }

Answer 82

Rabbit1 only.

Question 83

What is the output of the following code?

public class Plane {

public void fly(long l) {

System.out.print(“long “);

}

public static void main(String[] args) {

Plane p = new Plane();

p. fly(123);
p. fly(123L);

}}

Answer 83

long long

Question 84

What is the output of the following code?

public class Glider2 {

public static String glide(String s) { return “1”; }

public static String glide(String… s) { return “2”; }

public static String glide(Object o) { return “3”; }

public static String glide(String s, String t) { return “4”; }

public static void main(String[] args) {

System.out.print(glide(“a”));

System.out.print(glide(“a”, “b”));

System.out.print(glide(“a”, “b”, “c”));

}}

Answer 84

142

Question 85

When Java automatically creates you a do-nothing constructor, what is that constructor known as?

Answer 85

The default constructor.

Question 86

What is the problem with the following code?

public class Bunny {

private int length;

private int height;

public Bunny(int length, int height) {

length = this.length;

} }

Answer 86

This line should have the variables reversed:

length = this.length;

Question 87

What is the output of the following code?

public class Plane {

public void fly(int l) {

System.out.print(“int “);

}

public static void main(String[] args) {

Plane p = new Plane();

p.fly((int) 123L);

} }

Answer 87

int

Question 88

When the do-nothing constructor is created, in which file will you find it?

Answer 88

The .class file.

Question 89

What is the output of the following code?

public class YetMoreInitializationOrder {

static { add(2); }

static void add(int num) { System.out.print(num + “ “); }

YetMoreInitializationOrder() { add(5); }

static { add(4); }

{ add(6); }

static { new YetMoreInitializationOrder(); }

{ add(8); }

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

}

Answer 89

2 4 6 8 5

Question 90

true/false, the following code compiles:

public Hamster(int weight) {

System.out.println(“in the constructor”);

// ready to call this

this(weight, “brown”);

}

Answer 90

false. The “this” keyword must be the first non commented line in the constructor.

Question 91

What happens when the single parameter constructor is called?

public class Hamster {

private String color;

private int weight;

public Hamster(int weight, String color) {

this. weight = weight;
this. color = color;

}

public Hamster(int weight) {

new Hamster(weight, “Brown”);

}}

Answer 91

The code compiles, but because we are instantiating a new object with the “new” keyword yet not assigning it anywhere, the object we just created gets ignored. The correct way to handle this is to replace this:

new Hamster(weight, “Brown”);

with this:

this(weight, “Brown”);

Question 92

Which keyword do you use to call one constructor from within another constructor?

Answer 92

this

Question 93

What is the output of the following code?

public class InitializationOrderSimple {

private String name = “Torchie”;

{ System.out.println(name); }

private static int COUNT = 0;

static { System.out.println(COUNT); }

static { COUNT += 10; System.out.println(COUNT); }

public InitializationOrderSimple() {

System.out.println(“constructor”);

}}

public class CallInitializationOrderSimple {

public static void main(String[] args) {

InitializationOrderSimple init = new InitializationOrderSimple();

}}

Answer 93

0

10

Torchie

constructor

Question 94

What is the order of initialization?

Answer 94

1. initialize superclass first
2. Static variables and initializers in the order they appear.
3. Instance variables and initializers in the order they appear.
4. Constructors

Question 95

What is the special rule about using the “this” keyword to call one constructor from another constructor?

Answer 95

It must be the first noncommented statement in the constructor.

Question 96

What is the output of the following code?

public class Hamster {

private String color;

private int weight;

public Hamster(int weight, String color) {

this. weight = weight;
this. color = color;

}

public Hamster(int weight) {

Hamster(weight, “Brown”);

} }

Answer 96

Compiler error on this line:

Hamster(weight, “Brown”);

A constructor can be called only by writing ‘new’ before the name of the constructor.

Question 97

You can have multiple constructors in the same class as long as what?

Answer 97

As long as they have different method signatures.

Question 98

What is the output of the following code?

public class InitializationOrder {

private String name = “Torchie”;

{ System.out.println(name); }

private static int COUNT = 0;

static { System.out.println(COUNT); }

{ COUNT += 10; System.out.println(COUNT); }

public InitializationOrder() { System.out.println(“constructor”);

} }

public class CallInitializationOrderSimple {

public static void main(String[] args) {

System.out.println(“ready to construct”);

new InitializationOrder();

} }

Answer 98

ready to construct

0

Torchie

10

constructor

Question 99

true/false, the following code compiles:

public class MouseHouse {

private final int volume;

private final String name = “The Mouse House”;

public MouseHouse(int length, int width, int height) {

volume = length * width * height;

} }

Answer 99

true. Instance variables marked final can have their value assigned in a constructor.

Question 100

How can you make an encapsulated class immutable?

Answer 100

Do not include any setter methods. Do any assigning of variables in the constructor.

Question 101

What is the output of the following code?

public class Sb {

private StringBuilder builder;

public Sb(StringBuilder sb) {

builder = new StringBuilder(sb);

}

public StringBuilder getBuilder() {

return new StringBuilder(builder);

}

public static void main(String[] args) {

StringBuilder sb = new StringBuilder(“initial”);

Sb prob = new Sb(sb);

sb.append(“ added”);

StringBuilder gotBuilder = prob.getBuilder();

gotBuilder.append(“ more”);

System.out.println(prob.getBuilder());

} }

Answer 101

initial

Question 102

What is a lambda expression?

Answer 102

It is a block of code that gets passed around.

Question 103

Which of the following lines follow JavaBeans naming conventions for encapsulation?

private boolean playing;

private String name;

public boolean getPlaying() { return playing; }

public boolean isPlaying() { return playing; }

public String name() { return name; }

public void updateName(String n) { name = n; }

public void setname(String n) { name = n; }

Answer 103

private boolean playing; // yes

private String name; // yes

public boolean getPlaying() { return playing; } // yes

public boolean isPlaying() { return playing; } // yes

public String name() { return name; } // no

public void updateName(String n) { name = n; } // no

public void setname(String n) { name = n; } // no

Question 104

What is meant by encapsulation?

Answer 104

We set up the class so only methods in the class with the variables can refer to the instance variables.

Question 105

What is the output of the following code?

public class Sb {

private StringBuilder builder;

public Sb(StringBuilder sb) {

builder = sb;

}

public StringBuilder getBuilder() { return builder; }

public static void main(String[] args) {

StringBuilder sb = new StringBuilder(“initial”);

Sb prob = new Sb(sb);

sb.append(“ added”);

StringBuilder gotBuilder = prob.getBuilder();

gotBuilder.append(“ more”);

System.out.println(prob.getBuilder());

} }

Answer 105

initial added more

Question 106

Is this a valid call to a Lambda expression?

a,b -> a.startsWith(“test”);

Answer 106

no. needs parenthesis around the parameter list.

Question 107

Is this a valid call to a Lambda expression? () -> true;

Answer 107

yes

Question 108

In what package is the Predicate interface?

Answer 108

java.util.function

Question 109

What is the output of the following code?

List bunnies = new ArrayList<>();

bunnies. add(“long ear”);
bunnies. add(“floppy”);
bunnies. add(“hoppy”);

System.out.println(bunnies);

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

System.out.println(bunnies);

Answer 109

[long ear, floppy, hoppy]

[hoppy]

Question 110

What is deferred execution?

Answer 110

It means that the code is specified now but will run later.

Question 111

Is this a valid call to a Lambda expression?

a -> a.startsWith(“test”);

Answer 111

yes

Question 112

Is this a valid call to a Lambda expression?

(a,b) -> a.startsWith(“test”);

Answer 112

yes

Question 113

When constructing a lambda expression, when should you put parenthesis around the parameter list?

Answer 113

Always, except when you just have one parameter and it doesn’t specify the data type.

Question 114

When java tries to find the best overloaded method, in what order does it look through the overloaded methods?

Answer 114

Exact match

wider primitives

autoboxing

varargs

Question 115

Is this a valid call to a Lambda expression?

(String a, String b) -> a.startsWith(“test”);

Answer 115

yes

Question 116

What is an interface with just one method called?

Answer 116

A functional interface.

Question 117

“Encapsulation” refers to what?

Answer 117

Preventing callers from changing the object’s instance variables directly.

Question 118

Is this a valid call to a Lambda expression?

(String a) -> a.startsWith(“test”);

Answer 118

yes

Question 119

Is this a valid call to a Lambda expression?

a -> { return a.startsWith(“test”) }

Answer 119

no. missing a semicolon.

Question 120

A functional interface can be used with what type of programming?

Answer 120

functional programming

Question 121

When working with a Lambda expression, when can braces and the return statement be omitted?

Answer 121

When there’s a single statement. a -> a.equals(b)

Question 122

Is this a valid call to a Lambda expression?

a -> { a.startsWith(“test”); }

Answer 122

no. missing the “return” keyword.

Question 123

Is this a valid call to a Lambda expression?

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

Answer 123

no. you can’t redeclare a parameter inside the body.

Question 124

What happens to your lambda expression if your functional interface has more than one method?

Answer 124

It doesn’t compile.

Question 125

What is the name of the special predicate built into the ArrayList class?

Answer 125

removeIf()