CMSC 131 (Summer 2019) Week 02 Study Questions

Question 1

When your Java program is compiled, what type of file is created? (Hint: It is NOT machine language.)

Answer 1

bytecode

Question 2

What does it mean for someone to say that a Java program is “portable”?

Answer 2

The same bytecode will run successfully on any platform (provided that the Java Virtual Machine (JVM) is available.)

Question 3

TRUE/FALSE: Inserting unnecessary spaces and/or blank lines could cause your Java program to malfunction.

Answer 3

FALSE

Question 4

List the four Java primitive types that can be used to store integer values.

Answer 4

long, int, short, byte

Question 5

How much memory is required to store each of the four types mentioned in the previous question?

Answer 5

long: 8
int: 4
short: 2
byte: 1

Question 6

What advantage do you gain from using one of the types of integer types that requires MORE memory?

Answer 6

You can store a wider range of values (larger values).

Question 7

List the two Java primitive types that can be used to store floating point values.

Answer 7

float, double

Question 8

How much memory is required to store each of the two types mentioned in the previous question?

Answer 8

double: 8
float: 4

Question 9

What advantage do you gain from using double instead of float?

Answer 9

more precision (it will retain more digits)

Question 10

List the two Java types that are used to store values that are not numbers.

Answer 10

char and boolean

Question 11

Write a statement that declares a variable named counter of type int, and stores the value 182 in the variable.

Answer 11

int counter = 182;

Question 12

Write a statement that simultaneously declares three variables of type boolean, named x, y, and z.

Answer 12

boolean x, y, z;

Question 13

What values can a boolean variable achieve?

Answer 13

true or false

Question 14

Write a java class called “Fred”. Put in a main method. Have the main method store your age in a variable named age. Then main should print out a line that has your name, followed by your age. (Use a ?string literal? for your name, but use the variable to access your age.)

Answer 14

public class Fred {
      public static void main(String[] args) {
        int age = 12;
        System.out.println("Fawzi Emad, age is " + age);
      }
    }

Question 15

Practice using BOTH styles for Java comments.

Answer 15

// comment using first style

/* comment using second style */

Question 16

Is the following statement valid: int x = 34.7;

Answer 16

no

Question 17

Is the following statement valid: double y = 12;

Answer 17

yes

Question 18

Is the following statement valid: boolean q = 17 < 25;

Answer 18

yes

Question 19

Evaluate the following Java expression: 9 - 15 * 6 / 11 + 4

Answer 19

5

Question 20

Evaluate the following Java expression: 75 % 7

Answer 20

5

Question 21

Never forget that you should not compare two Strings with the == operator. Suppose you have two String variables, x and y. Give an expression that can be used to check whether or not the Strings x and y are identical.

Answer 21

x.equals(y)

Question 22

What is “concatenation”? What operator do you use to concatenate Strings?

Answer 22

+

Question 23

What is the difference between System.out.print and System.out.println?

Answer 23

System.out.println moves the cursor down to the next line after it does it’s output.

Question 24

Suppose you have a String variable called s. What expression will return the number of characters in the String?

Answer 24

s.length()

Question 25

Give examples of "literals" of each of the following types: String, char, long, int, float, double, boolean.

Answer 25

"hi", 'x', 32L, 16, 15.7F, 373.2, true

Question 26

What "escape sequence" would you use in a String to indicate a "new line"?

Answer 26

\n

Question 27

What is the difference between "syntax errors" and "logical errors"?

Answer 27

Syntax errors are due to your failure to follow the rules of the language. Logical errors are where you have written a valid Java program, but it does not behave the way it should.

Question 28

If your program compiles and runs, but behaves incorrectly, are you probably suffering from "syntax" or "logical" errors?

Answer 28

logical

Question 29

If Eclipse flags your code with a red mark and won't let you compile it, are you suffering from "syntax" or "logical" errors?

Answer 29

syntax