CSS 142 Multiple Choice Midterm

Can Java have two variables named name and Name?

Yes, always

What output is produced by:

String greetings = "Hello" + " there " + "earthling";
System.out.println(greetings);

Hello there earthling

Consider the following code:

System.out.println("Please tell us your name");

Scanner keyboardInput = new Scanner(System.in);

What can you do to make sure the input is read?

The code is incomplete

Needs to have something like

String fullName = userInput.nextLine();

There are only two basic types of methods..

Methods that returns a value and methods that do not.

What is the syntax for importing a scanner?

import java.util.*;

How do you declare a variable?

variableType variableName

i.e. double decimals

What does the following boolean expression evaluate to?

((a < 100) && (!(a == 66) || (a == 77)))

True whenever a is less than 100 and is not 66 (or equal to 77); false otherwise

How do you change a variable's type?

By casting,

int b = 0;

(double)b

How to import math?

What are methods you can use within math?

Don't need to import math

Math.abs();

Math.hypot(double x, double y)

Math.max/min(2 numbers);

Math.sqrt();

If boolean variable P is true and Q is false, what is !(P || Q)?

false

What is the value of e?

int a = 4;

int b = 3;

double c = 3.2;

double d = 1.0;

double e;

if ((a / b) < (b / a)) {

e = c / d;

} else {

e = a / b;

}

1.0

First, performs a/b as ints then converts the answer to double

Syntax for switch statements

switch (value being compared to)

{

case 1:

code

break;

case 2;

code

break;

}

when value is equal to case #, the statement executes

int n = 10;

do

{

System.out.println(n);

n = n - 3;

} while (n > 0);

10

7

4

1

What is the output of the following?

for (int count = 1; count < 5; count++)

System.out.print((2 * count) + " ");

2 4 6 8

public static void whileMystery(int x, int y, int z) {

while (x < z || y < z) {

x = x + y;

y = y * 2;

System.out.print(x + " " + y + " ");

}

System.out.println();

}

5 10 15 20

A while loop

will execute if its test condition is true.

What is the expression num *= 3 equivalent to?

num = num * 3;

The boolean, int, and double variable types are examples of

primitive types

A do-while loop

will always execute at least once.

a = false;

b = true;

c = 5 < 3;

x = !( a & b & c) == ( !a | !b | !c);

What is x equal to?

true

Data types of arrays can be

Of any data type, including an array data type

What is the correct way to create an empty integer array that contains 3 elements?

int[] arr = new int[3];

What is wrong with the following code?

int[] nums = 0;

0 is not a valid value for an integer array

What is the outcome of the following code?

int[] a = { 1 , 2, 3, 4, 5 };

int[] b = { 7, 8, 9, 10 };

b = a;

b[4] = 99;

System.out.println(a[4]);

99

A constructor

is executed when an instance is created

Instance variables

are class-level variables

Actions in a class object

are typically non-static methods

Assume a class "Cat" with a toString() method. Which of these would be an acceptable return value?

All of these are acceptable return values for a toString() method

The cat's name

A string that includes all of the Cat instance's properties

"Bob"

All of these are acceptable return values for a toString() method

Assume a class "Dog" with an equals() method.

Which of these would be an acceptable comparison between "this" Dog instance and "another" Dog instance?

Comparison of only Dog's memory locations

Comparison of all Dog's properties

All of these are acceptable comparisons between Dog instances

Comparison of only Dog's name

All of these are acceptable comparisons between Dog instances

Given a class "Ball" with a "radius" property and "getArea()" method, which of these would be an appropriate return statement for a toString() method?

Any of these return statements would be appropriate

return ("Area = " + getArea());

return ("This is a circle.");

return ("Radius = " + this.radius);

Any of these return statements would be appropriate

Which is likely a proper implementation of the "equals" method?

Comparing the values of instance variables that are of primitive data types

Given the following Class

public class LightSaber

{

private static String color;

public LightSaber(String c)

{

this.color = c;

}

}

Let's assume that we create the following in a Driver class:

LightSaber sith = new LightSaber("red");

LightSaber luke = new LightSaber("blue");

LightSaber yoda = new LightSaber("green");

What is the color of the "sith" light saber after the "yoda" light saber is created?

green

What is the main difference between the "while" loop and the "do/while" loop?

The do/while loop is guaranteed to "run" at least once

What is the outcome of the following code?

int sum = 0;

for(int i = 0; i < 10; i++)

{

for(int j = 0; j < 10; j++)

{

sum++;

}

}

sum is 100

int sum = 0;

for(int i = 0; i < 10; i++)

{

for(int j = 0; i < 10; i++)

{

sum++;

}

}

What is sum?

10

What will happen when the following code executes?

int sum = 0;

for(int i = 0; i < 10; i++)

{

for(int j = 0; j < 10; i++)

{

sum++;

}

}

endless loop

The this keyword

refers to the calling instance object.

How many elements is in an array thisArray?

thisArray.length;

A class that has a main method

can be a main program.

Consider the following code:

int[] a = {4, 7, 2, 1, -2};

int[] b = {a[0], a[1], a[2], a[3], a[4]};

a[2] = a[1] * 3;

b[1] = a[2] - 9;

What is the contents of a after this code is executed?

4, 7, 21, 1, -2

How many iterations will the following loop go through? (I.e., how many times is the loop body executed?)

for (int i = 2; (i > 1) && (i < 10); i = i+2)

{

System.out.println(i);

i = i - 1;

i = 10 / i;

}

1

Object instance variables

store data associated with the object.

A properly written accessor method of a class

returns the value of private instance variables.

Consider the following code:

int[] a = {4, 7, 2, 1, -2};

int[] b = a;

a[2] = a[1] * 3;

b[1] = a[2] - 9;

What is the contents of a after this code is executed?

4, -7, 21, 1, -2

The instance of a class

follows the structure set by the class definition.

Which of the following code snippets creates an instance of the class MyClass?

MyClass aMyClass = new MyClass();

Object methods

act on data connected to or passed into the object.

What is the difference(s) between a public and private instance variable?

Private instance variables cannot be directly read or set while public instances variables can be directly read and set.

Two classes that each have a method of the same name

will work fine.

A properly written mutator method of a class

sets the value of private instance variables.