Java SE 17 Study Guide for Certification - Chapter 01

Java SE 17 Study Guide
Chapter 1
Bill Herman
WilliamRobertHerman@Gmail.com

Question 1
Which of the following are legal entry point
methods that can be run from the command
line? (Choose all that apply)
private static void main(String[] args)
public static final main(String[] args)
public void main(String[] args)
public static final void main(String[] args)
public static void main(String[] args)
public static main(String[] args)

Answer 1
Which of the following are legal entry point
methods that can be run from the command
line? (Choose all that apply)
private static void main(String[] args)
public static final main(String[] args)
public void main(String[] args)
public static final void main(String[] args)
public static void main(String[] args)
public static main(String[] args)
Comment: Final is optional

Question 2
What order of statements will
compile successfully?
class Rabbit {} import java.util.*;
package animals;
import java.util.*; package
animals; class Rabbit {}
package animals; import
java.util.*; class Rabbit {}
import java.util.*; class Rabbit {}
package animals; class Rabbit {}
class Rabbit {} package animals;
None of the above

Answer 2
What order of statements will compile
successfully?
class Rabbit {} import java.util.*;
package animals;
import java.util.*; package animals;
class Rabbit {}
package animals; import java.util.*;
class Rabbit {}
import java.util.*; class Rabbit {}
package animals; class Rabbit {}
class Rabbit {} package animals;
None of the above
Comment: package & import optional:
package then import then class

Question 3
Which of the following are true?
(Choose all that apply.)
public class Bunny {
public static void main(String[] x)
{
Bunny bun = new Bunny();
}
}
Bunny is a class.
bun is a class.
main is a class.
Bunny is a reference to an object.
bun is a reference to an object.
main is a reference to an object.
The main () method doesn't run
because the parameter name is
incorrect.

Question 4
Which of the following are valid
Java identifiers? (Choose all that
apply.)
_
_helloWorld$
true
java.lang
Public
1980_s
_Q2_

Answer 4
Which of the following are valid
Java identifiers? (Choose all that
apply.)
_ (single underscore not allowed)
_helloWorld$
true (reserved word)
java.lang (contains .)
Public
1980_s (starts with number)
_Q2_

Question 5
Which statements about the following program are correct?
2: public class Bear {
3: private Bear pandaBear;
4: private void roar(Bear b) {
5: System.out.println("Roar!");
6: pandaBear = b;
7: }
8: public static void main(String[] args) {
9: Bear brownBear = new Bear();
10: Bear polarBear = new Bear();
11: brownBear.roar(polarBear);
12: polarBear = null;
13: brownBear = null;
14: System.gc(); } }
The object created on line 9 is eligible for garbage collection
after line 13.
after line 14.
after line 12.
after line 13.
Garbage collection is guaranteed to run.
Garbage collection might or might not run.
The code does not compile.

Answer 5
Which statements about the following program are correct?
2: public class Bear {
3: private Bear pandaBear;
4: private void roar(Bear b) {
5: System.out.println("Roar!");
6: pandaBear = b;
7: }
9: Bear brownBear = new Bear();
10: Bear polarBear = new Bear();
11: brownBear.roar(polarBear);
12: polarBear = null;
13: brownBear = null;
14: System.gc(); } }
after line 13. (set to null)
after line 14. (new Bear())
after line 12. (new Bear())
after line 13. (set to null)
Garbage collection is guaranteed to run.
Garbage collection might or might not run.

Question 6
Assuming the following class compiles, how
many variables defined in the class or method
are in scope on the line marked on line 14?
1: public class Camel {
2: { int hairs = 3_000_0; }
3: long water, air=2;
4: boolean twoHumps = true;
5: public void spit(float distance) {
6: var path = "";
7: { double teeth = 32 + distance++; }
8: while(water > 0) { int age = twoHumps
? i : 2; Short i=-i; for(i=0; i<10; i++) {var Private
= 2; { // SCOPE } } }
2
3
4
5
6
7
None of the above

Question 6
Assuming the following class compiles, how
many variables defined in the class or method
are in scope on the line marked at // SCOPE?
1: public class Camel {
2: { int hairs = 3_000_0; }
3: long water, air=2;
4: boolean twoHumps = true;
5: public void spit(float distance) {
6: var path = "";
7: { double teeth = 32 + distance++; }
8: while(water > 0) { int age = twoHumps
? i : 2; Short i=-i; for(i=0; i<10; i++) {var Private
= 2; { //
SCOPE } } }
2
3
4
5
6
7
None of the above

Question 7
Which are true about this code? (Choose all that
apply.)
public class KitchenSink {
private int numForks;
public static void main(String[] args) {
int numKnives;
System.out.print("""
"# forks = " + numForks +
" # knives = " + numKnives +
# cups = 0""");
}
}
The output includes: # forks = 0.
The output includes: # knives = 0.
The output includes: # cups = 0.
The output includes a blank line.
The output includes one or more lines that
begin with whitespace.

Answer 7
Which are true about this code? (Choose all that
apply.)
public class KitchenSink {
private int numForks;
int numKnives;
System.out.print("""
"# forks = " + numForks +
" # knives = " + numKnives +
# cups = 0""");
}
}
The output includes: # forks = 0.
The output includes: # knives = 0.
The output includes: # cups = 0.
The output includes a blank line.
The output includes one or more lines that
begin with whitespace.
Comment: forks and knives are never used

Question 8
Which of the following code
snippets about var compile
without issue when used in a
method? (Choose all that apply.)
var spring = null;
var fall = "leaves";
var evening = 2; evening = null;
var night = Integer.valueof(3);
var day = 1/0;
var winter = 12, cold;
var fall = 2, autumn = 2;
var morning = ""; morning = null;

Answer 8
Which of the following code
snippets about var compile
without issue when used in a
method? (Choose all that apply.)
var spring = null;
var fall = "leaves";
var evening = 2; evening = null;
var night = Integer.valueof(3);
var day = 1/0;
var winter = 12, cold;
var fall = 2, autumn = 2;
var morning = ""; morning = null;
Comment: var not allowed multi

Question 9
Which of the following are correct?
An instance variable of type float
defaults to 0.
An instance variable of type char
defaults to null.
A local variable of type double defaults
to 0.0.
A local variable of type int defaults to
null.
A class variable of type String defaults
to null.
to the empty string "".
None of the above.

Answer 9
Which of the following are correct?
An instance variable of type float
defaults to 0.
An instance variable of type char
defaults to null.
A local variable of type double defaults
to 0.0.
A local variable of type int defaults to
null.
to null.
to the empty string "".
None of the above.

Question 10
Which of the following expressions,
when inserted independently into
the blank line, allow the code to
compile? (Choose all that apply.)
public void printMagicData() {
var magic =
___________________;
System.out.println (magic) ;
}
3_1
1_329_.0
3_13.0_
5_291._2
2_234.0_0
9___6
_1_3_5_0

Answer 10
Which of the following expressions,
when inserted independently into
the blank line, allow the code to
public void printMagicData() {
var magic =
___________________;
System.out.println (magic) ;
}
3_1
1_329_.0
3_13.0_
5_291._2
2_234.0_0
9___6
_1_3_5_0
Comment: _ is legal if not at the
beginning or end or next to “.”

Question 11
Given the following two class files, what is the
maximum number of imports that can be
removed and have the code still compile?
// Water.java
package aquarium;
public class Water { }
// Tank.java
package aquarium;
import java.lang.*; import java.lang.System;
import aquarium.Water; import aquarium.*;
public class Tank {
public void print(Water water) {
System.out.println(water); } }
0
1
2
3
4
Does not compile

Answer 11
Given the following two class files, what is the
maximum number of imports that can be
removed and have the code still compile?
// Water.java
package aquarium;
public class Water { }
// Tank.java
package aquarium;
import java.lang.*; import java.lang.System;
import aquarium.Water; import aquarium.*;
public class Tank {
public void print(Water water) {
System.out.println(water); } }
0
1
2
3
4
Does not compile
Comment: java.lang included as default.
Aquarium already imported.

Question 12
Which statements about the following class
are correct? (Choose all that apply.)
1: public class ClownFish {
2: int gills = 0, double weight=2;
3: { int fins = gills; }
4: void print(int length = 3) {
5: System.out.println(gills);
6: System.out.println(weight);
7: System.out.println(fins);
8: System.out.println(length);
9:} }
Line 2 generates a compiler error.
The code prints 0.
The code prints 2.0.
The code prints 2.
The code prints 3.

Answer 12
are correct? (Choose all that apply.)
1: public class ClownFish {
2: int gills = 0, double weight=2;
3: { int fins = gills; }
4: void print(int length = 3) {
5: System.out.println(gills);
6: System.out.println(weight);
7: System.out.println(fins);
8: System.out.println(length);
9:} }
The code prints 0.
The code prints 2.0.
The code prints 2.
The code prints 3.
Comment: Line 2 is invalid because
different types and comma instead of semi-
colon. Line 4 is not a valid parameter
signature.

Question 13
Given the following classes, which of the
following snippets can independently be
inserted in place of INSERT IMPORTS HERE
and have the code compile? (Choose all
that apply.)
package aquarium;
public class Water { boolean salty = false; }
package aquarium.jellies;
public class Water { boolean salty = true;}
package employee;
INSERT IMPORTS HERE
public class WaterFiller { Water water; }
import aquarium.*;
import aquarium.Water; import
aquarium.jellies.*;
import aquarium.*; import
aquarium.jellies.Water;
aquarium.jellies.*;
None of these imports can make the code
compile.

Answer 13
Given the following classes, which of the
following snippets can independently be
inserted in place of INSERT IMPORTS HERE
and have the code compile? (Choose all
that apply.)
package aquarium;
public class Water { boolean salty = false; }
package aquarium.jellies;
public class Water { boolean salty = true;}
package employee;
INSERT IMPORTS HERE
public class WaterFiller { Water water; }
import aquarium.*;
aquarium.jellies.*;
aquarium.jellies.*;
None of these imports can make the code
compile.
Comment: Duplicate class name (Water)
not selected correctly.

Question 14
Which of the following statements
about the code snippet are
true?(Choose all that apply.)
3: short numPets = 5L;
4: int numGrains = 2.0;
5: String name = "Scruffy";
6: int d = numPets.length();
7: int e = numGrains.length;
8: int f = name.length();

Answer 14
about the code snippet are
true?(Choose all that apply.)
3: short numPets = 5L;
4: int numGrains = 2.0;
5: String name = "Scruffy";
6: int d = numPets.length();
7: int e = numGrains.length;
8: int f = name.length();

Question 15
Which of the following statements about
garbage collection are correct? (Choose all that
apply.)
Calling System.gc( ) is guaranteed to free up
memory by destroying objects eligible for
garbage collection.
Garbage collection runs on a set schedule.
Garbage collection allows the JVM to reclaim
memory for other objects.
Garbage collection runs when your program has
used up half the available memory.
An object may be eligible for garbage collection
but never removed from the heap.
An object is eligible for garbage collection once
no references to it are accessible in the
program.
Marking a variable final means its associated
object will never be garbage collected.

Answer 15
Which of the following statements about
garbage collection are correct? (Choose all that
apply.)
Calling System.gc( ) is guaranteed to free up
memory by destroying objects eligible for
garbage collection.
Garbage collection runs on a set schedule.
Garbage collection allows the JVM to reclaim
memory for other objects.
Garbage collection runs when your program has
used up half the available memory.
An object may be eligible for garbage collection
but never removed from the heap.
An object is eligible for garbage collection once
no references to it are accessible in the
program.
Marking a variable final means its associated
object will never be garbage collected.

Question 16
Which are true about this code?
var blocky = """
squirrel s
pigeon
termite""";
System.out.print(blocky);
It outputs two lines.
It outputs three lines.
It outputs four lines.
There is one line with trailing
whitespace.
There are two lines with trailing
whitespace.
If we indented each line five
characters, it would change the
output.

Answer 16
Which are true about this code?
var blocky = """
squirrel s
pigeon
termite""";
System.out.print(blocky);
It outputs two lines.
It outputs three lines.
It outputs four lines.
There is one line with trailing
whitespace.
There are two lines with trailing
whitespace.
If we indented each line five
characters, it would change the
output.
Comment: s = keep white space,
means remove line break

Question 17
What lines are printed by the following program?
1: public class WaterBottle {
2: private String brand;
3: private boolean empty;
4: public static float code;
6: WaterBottle wb = new WaterBottle();
7: System.out.println("Empty = " + wb.empty);
8: System.out.println("Brand = " + wb.brand);
9: System.out.println("Code = " + code);
10: } }
Empty =
Empty = false
Brand =
Brand = null
Code = 0.0
Code = 0f

Answer 17
What lines are printed by the following program?
1: public class WaterBottle {
2: private String brand;
3: private boolean empty;
4: public static float code;
6: WaterBottle wb = new WaterBottle();
7: System.out.println("Empty = " + wb.empty);
8: System.out.println("Brand = " + wb.brand);
9: System.out.println("Code = " + code);
10: } }
Empty =
Empty = false
Brand =
Brand = null
Code = 0.0
Code = 0f
Comment: printed values are defaults

Question 18
about var are true? (Choose all that
apply.)
A var can be used as a constructor
parameter.
The type of a var is known at compile
time.
A var cannot be used as an instance
variable.
A var can be used in a multiple variable
assignment statement.
The value of a var cannot change at
runtime.
The type of a var cannot change at
runtime.
The word var is a reserved word in Java.

Answer 18
about var are true? (Choose all that
apply.)
A var can be used as a constructor
parameter.
The type of a var is known at compile
time.
A var cannot be used as an instance
variable.
A var can be used in a multiple variable
assignment statement.
The value of a var cannot change at
runtime.
The type of a var cannot change at
runtime.
The word var is a reserved word in Java.

Question 19
Which are true about the
following code? (Choose all that
apply.)
var num1 =
Long.parseLong(“100");
var num2 = Long.valueof("100");
System.out.println(Long.max(num
1, num2)) ;
The output is 100.
The output is 200.
num1 is a primitive.

Answer 19
Which are true about the
following code? (Choose all that
apply.)
var num1 =
Long.parseLong(“100");
var num2 = Long.valueof("100");
System.out.println(Long.max(num
1, num2)) ;
The output is 100.
The output is 200.

Question 20
Which statements about the following class are
correct? (Choose all that apply.)
public class PoliceBox {
String color; long age;
public void PoliceBox() { color = "blue"; age =
1200; }
public static void main(String []time)
{var p = new PoliceBox(); var q = new
PoliceBox();
p.color = "green"; p.age = 1400; p=q;
System.out.println("Q1="+q.color + “
Q2="+q.age+ "P1="+p.color + “ P2="+p.age);
} }
It prints Q1=blue.
It prints Q2=1200.
It prints P1=null.
It prints P2=1400.
“public void PoliceBox()” does not compile.
“p.age = 1400; “ does not compile.
“p=q;” does not compile.
None of the above.

Answer 20
correct? (Choose all that apply.)
public class PoliceBox {
String color; long age;
public void PoliceBox() { color = "blue"; age =
1200; }
public static void main(String []time)
{var p = new PoliceBox(); var q = new
PoliceBox();
p.color = "green"; p.age = 1400; p=q;
System.out.println("Q1="+q.color + “
Q2="+q.age+ "P1="+p.color + “ P2="+p.age);
} }
It prints Q1=blue.
It prints Q2=1200.
It prints P1=null.
It prints P2=1400.
“public void PoliceBox()” does not compile.
“p.age = 1400; “ does not compile.
“p=q;” does not compile.
None of the above.
Comment: public void PoliceBox() is a method,
not a constructor.

Question 21
What is the output of executing the
following class?
public class Salmon {
int count; { System.out.print(count+"-
"); }
{ Count++; }
public Salmon() { count = 4;
System.out.print(2+"-") ;}
System.out.print(7+"') ;
var s = new salmon();
System.out.print(s.count+“-"); } }
7-0-2-1
7-0-1-
0-7-2-1-
7-0-2-4-
0-7-1-
The class does not compile because of
“{ System.out.print(count+"-"); }”.
“public Salmon()“.
None of the above.

Answer 21
What is the output of executing the
following class?
public class Salmon {
int count; { System.out.print(count+"-
"); }
{ Count++; }
public Salmon() { count = 4;
System.out.print(2+"-") ;}
System.out.print(7+"') ;
var s = new salmon();
System.out.print(s.count+“-"); } }
7-0-2-1
7-0-1-
0-7-2-1-
7-0-2-4-
0-7-1-
“{ System.out.print(count+"-"); }”.
“public Salmon()“.
None of the above.
Comment: start at main

Question 22
Given the following class, which of
the following lines of code can
independently replace INSERT
CODE HERE to make the code
public class Price {
public void admission() {
INSERT CODE HERE
System.out.print(amount);
} }
int Amount = 0b11;
int amount = 9L;
int amount = 0xE;
int amount = 1_2.0;
double amount = 1_0_.0;
int amount = 0b101;
double amount = 9_2.1_2;
double amount = 1_2_.0_0;

Answer 22
Given the following class, which of
the following lines of code can
independently replace INSERT
CODE HERE to make the code
public class Price {
public void admission() {
INSERT CODE HERE
System.out.print(amount);
} }
int Amount = 0b11;
int amount = 9L;
int amount = 0xE;
int amount = 1_2.0;
double amount = 1_0_.0;
int amount = 0b101;
double amount = 9_2.1_2;
double amount = 1_2_.0_0;
Comment: _. or ._ = invalid

Question 23
are true? (Choose all that apply.)
public class River {
int Depth = 1; float temp = 50.0;
public void flow() {
for (int i = 0; i < 1; i++) {int depth = 2;
depth++; temp--;}
System.out.println(depth);
System.out.println(temp); }
public static void main(String... s) {
new River().flow(); } }
“float temp = 50.0;” generates a compiler
error.
“int depth = 2;” generates a compiler error.
“depth++;” generates a compiler error.
“System.out.println(depth);” generates a
compiler error.
The program prints 3 at
“System.out.println(depth);”.
The program prints 50.0 at
“System.out.println(temp);“.
“System.out.println(temp);”.

Answer 23
true? (Choose all that apply.)
public class River {
int Depth = 1; float temp = 50.0;
public void flow() {
for (int i = 0; i < 1; i++) {int depth = 2;
depth++; temp--;}
System.out.println(depth);
System.out.println(temp); }
public static void main(String... s) {
new River().flow(); } }
“float temp = 50.0;” generates a compiler error.
“int depth = 2;” generates a compiler error.
“depth++;” generates a compiler error.
“System.out.println(depth);” generates a
compiler error.
“System.out.println(temp);“.
“System.out.println(temp);”.
Comment: 50.0 needs “f” and depth is out of
scope at println

15 minute break
This is the end of chapter 1.
Chapter 2 will resume after the break.

Java SE 17 Study Guide for Certification - Chapter 01

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