CMSC 131 Study Questions 2

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

What is the difference between “syntax errors” and “logical errors”?

Answer 4

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 5

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

Answer 5

logical

Question 6

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 6

syntax

Question 7

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

Answer 7

long, int, short, byte

Question 8

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

Answer 8

long 8, int 4, short 2, byte 1

Question 9

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

Answer 9

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

Question 10

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

Answer 10

float and double

Question 11

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

Answer 11

float 4, double 8

Question 12

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

Answer 12

more precision (it will retain more digits)

Question 13

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

Answer 13

char and boolean

Question 14

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

Answer 14

int conter = 182;

Question 15

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

Answer 15

boolean x, y, z;

Question 16

What values can a boolean variable achieve?

Answer 16

true or false

Question 17

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 17

public class Fred {
      public static void main(String[] args) {
                  int age = 38;
                  System.out.println("Your name here, age is " + age);
      }
}

Question 18

Practice using BOTH styles for Java comments.

Answer 18

// comment using first style

/* comment using second style */

Question 19

Is the following statement valid: int x = 34.7;

Answer 19

NO – you can’t force Java to store a floating point value in an integer variable.

Question 20

Is the following statement valid: double y = 12;

Answer 20

YES

Question 21

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

Answer 21

YES

Question 22

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

Answer 22

5

Question 23

Evaluate the following Java expression: 75 % 7

Answer 23

5

Question 24

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 24

x.equals(y)

Question 25

What is "concatenation"? What operator do you use to concatenate Strings?

Answer 25

Joining two Strings into one larger string. Use the + operator.

Question 26

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

Answer 26

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

Question 27

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

Answer 27

s.length()

Question 28

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

Answer 28

String: "Hello" char: 'x' long: 17L int: 17 float: 3.14F double: 3.14 boolean: true

Question 29

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

Answer 29

\n